Platinum Group Metals and Compounds;: A symposium sponsored by the Division of Inorganic Chemistry at the 158th meeting of the American Chemical Society (Advances in chemistry series 098)

Platinum

Group

Metals

and Compounds

A symposium sponsored by Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

the Division of Inorganic Chemistry at the 158th Meeting of the American Chemical Society, New York, Ν. Y . , Sept. 8-9, 1969. U. V. Rao Symposium Chairman

ADVANCES

IN

CHEMISTRY

SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C.

1971

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

98

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

Coden:

ADCSHA

Copyright © 1971 American Chemical Society All Rights Reserved

Library of Congress Catalog Card 76-152,755 ISBN 8412-0135-8 PRINTED IN THE UNITED STATES OF AMERICA In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

A d v a n c e s in C h e m i s t r y Series

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

Robert F. Gould, Editor

Advisory Board Paul N. Craig Thomas H. Donnelly Gunther Eichhorn Frederick M. Fowkes Fred W. McLafferty William E. Parham Aaron A. Rosen Charles N. Satterfield Jack Weiner

AMERICAN CHEMICAL SOCIETY PUBLICATIONS

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.fw001

FOREWORD

ADVANCES

IN CHEMISTRY

SERIES

w a s f o u n d e d i n 1949 b y the

A m e r i c a n C h e m i c a l S o c i e t y as a n outlet for s y m p o s i a a n d c o l lections of d a t a in s p e c i a l areas of t o p i c a l interest that c o u l d n o t b e a c c o m m o d a t e d in the Society's journals. m e d i u m for s y m p o s i a that w o u l d o t h e r w i s e b e

It p r o v i d e s a fragmented,

t h e i r papers d i s t r i b u t e d a m o n g several journals or not

pub-

l i s h e d at all. P a p e r s are refereed c r i t i c a l l y a c c o r d i n g to ACS e d i t o r i a l standards a n d receive the c a r e f u l a t t e n t i o n a n d p r o c essing c h a r a c t e r i s t i c of ACS p u b l i c a t i o n s . in

ADVANCES

IN CHEMISTRY

SERIES

Papers p u b l i s h e d

are o r i g i n a l c o n t r i b u t i o n s

not p u b l i s h e d elsewhere i n w h o l e o r m a j o r p a r t a n d i n c l u d e reports of research as well as r e v i e w s since s y m p o s i a m a y e m b r a c e b o t h types of

presentation.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.pr001

PREFACE

lmost every chemist is aware of the fact that platinum group metal chemistry usually centers around the phenomenon of catalysis. Other interesting phases of the chemistry of the platinum group metals which could be of interest to inorganic chemists are usually obscured by this singular though significant application. When I approached Eugene Rachow, Chairman of the Symposium Planning Committee of the Inor­ ganic Division of ACS, I had every intention of covering all facets of the platinum group metal chemistry. Because of the limitations of time, I was obliged to limit the symposium to four sessions. The material to be presented at the symposium was divided into four categories: (1) Synthe­ sis, Structure, Determination, and Study of Magnetic and Thermodynamic Properties of Platinum Group Metal Compounds, (2) Recent Chemistry of σ- and ττ-Bonded Complexes of Platinum Group Metals, (3) Spec­ troscopic Properties of Platinum Group Metal Compounds, (4) Newer Industrial Aspects of Platinum Group Metals and Their Compounds. Each category, by itself, can be a topic for a separate symposium, and it is hoped that in the future such symposia will be forthcoming. The topics chosen were such that they would cover a broad area of the chemistry of platinum group metals. The session on industrial aspects was included to enable scientists in industry to present their views on the problems that are facing the industry and perhaps stimulate sufficient interest so that newer applications could be developed in the future. It is also hoped that such a forum would enable scientists in industry to summarize broadly the work carried out by them without worry about violation of proprietary nature of the work. I would like to take this opportunity to extend my thanks to all the speakers at the symposium and to all the authors who contributed articles to this volume. I would also wish to express my gratitude to the manage­ ment of Matthey Bishop, Inc., who kindly permitted me to utilize their time and facilities to arrange this symposium. My special thanks to G. Cohn of Engelhard Industries and L. B. Hunt of Johnson Matthey & Co. for their cooperation and help rendered to find suitable speakers. U. V. RAO

Matthey Bishop, Inc. Malvern, Pa. 19355 December 1970 vii In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1

M a g n e t i c Properties o f the P l a t i n u m Metals a n d T h e i r A l l o y s H. J. ALBERT and L. R. RUBIN

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

Engelhard Minerals and Chemicals Corp., Newark, N. J. 07105 Although they are paramagnetic, the platinum metals, especially platinum, palladium, and rhodium, are capable of interacting in alloys with other metals to form ferromagnetic or very nearly ferromagnetic materials. Dilute additions of elements of the iron group and its neighbors with platinum and palladium take on enhanced moments which are interpreted as arising from an interaction of the solute moment with the 4d or 5d host electrons. Ferromagnetic and anti-ferromagnetic structures may result from greater additions of the iron group to the platinum metals. Examples are FeRh, Pt Fe, Pd Fe, and PtCo. Compounds of the rare earths with the platinum metals also form magnetic structures with unusual properties. 3

3

*Tphe platinum metals—ruthenium, rhodium, and palladium in the 2nd long row of the periodic system and osmium, iridium, and platinum in the 3rd long row—are all paramagnetic. That is, none of these elements have a permanent magnetic moment associated with it. However, as shown in Table I, the mass susceptibility of these elements varies widely over two orders of magnitude. Further, the "nonmagnetic" platinum metals are the elements immediately beneath the "magnetic" series iron-cobalt-nickel and, of course, are all in the transition group. Platinum, palladium, and rhodium form a number of ferromagnetic alloys with the iron group metals and with manganese. The present paper is not an exhaustive review but presents some of the more interesting magnetic work on the platinum metals which has appeared in the last 10-20 years. Palladium has the highest magnetic susceptibility of the platinum group, and because it is so high it has been termed an "incipient ferromagnet." The implication is that palladium could be induced to become A

1 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

P L A T I N U M

Table I.

GROUP

M E T A L S

A N D

C O M P O U N D S

Mass Susceptibility of the Platinum Metals (Χ

Ru(+0.427)»

10

- 6

cgs U n i t s )

Rh(+0.9903)

0

Pd(+5.231)

c

c

Os(+0.052) Ir(+0.133) Pt(+0.9712) ° Reprinted from Engelhard Industries Technical Bulletin. Determinations made at 25°C. Determinations made at 20°C. b

6

c

6

e

ferromagnetic.

I n a w e a k l y p a r a m a g n e t i c m a t e r i a l , t h e s u s c e p t i b i l i t y of

the m a t e r i a l is i n d e p e n d e n t of t e m p e r a t u r e .

F i g u r e 1 ( 3 9 ) shows this

to b e q u i t e true f o r r h o d i u m . P a l l a d i u m , o n t h e other h a n d , exhibits a s t r o n g t e m p e r a t u r e d e p e n d e n c e of s u s c e p t i b i l i t y w i t h a p e a k at about Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

7 0 ° K . T h i s has b e e n t a k e n i n the past as évidence f o r a n a n t i f e r r o m a g n e t i c t r a n s i t i o n . H o w e v e r , n e u t r o n d i f f r a c t i o n has s h o w n n o e v i d e n c e of a n t i f e r r o m a g n e t i s m , a n d i t n o w seems l i k e l y that this effect is c a u s e d b y the F e r m i surface of p a l l a d i u m b e i n g associated w i t h a n extremely sharp p e a k i n t h e density-of-states.

T h e s u s c e p t i b i l i t y vs. t e m p e r a t u r e

curve

f o r t h e p a l l a d i u m - 5 % r h o d i u m a l l o y i n d i c a t e s t h e s e n s i t i v i t y of p a l l a d i u m - b a s e d alloys to electron c o n c e n t r a t i o n a n d t h e density-of-states i n r e l a t i o n to the F e r m i l e v e l

(13).

I r o n i m p u r i t i e s g r e a t l y c o m p l i c a t e t h e s u s c e p t i b i l i t y measurements o n p a l l a d i u m . A s n o t e d a b o v e , p a l l a d i u m is close to b e i n g f e r r o m a g n e t i c ,

I200xl0"

6

1000

800

600 mol 400

200

0.

100

200

Temperature,

300

°K

Weiss, J . R. "Solid State Physics for Metallurgists," Pergamon f

Figure 1. The susceptibility (10~ ergs/gauss?/mole) for palladium, rhodium, and paUadium-5% rhodium as a function of temperature (39) e

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

Magnetic

A N D R U B I N

50

' ' ΊΟο' '

3

Properties

'

Ι5θ' ' ' T(°K)

ZOO' ' ' 250'

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

Journal of Applied Physics

Figure 2. Susceptibility vs. temperature for several "pure" palladium samples (17) φ 3 ppm iron, Ο 2 ppm iron, Δ zone refined, solid line less than 1 ppm iron

TCK)

Journal of Applied

Physics

Figure 3. Susceptibility vs. temperature for phtinum with approximately 3 ppm of iron (17)

a n d s m a l l a d d i t i o n s of i r o n w i l l f o r m f e r r o m a g n e t i c alloys w i t h

Curie

temperatures i n t h e c r y o g e n i c range. T h u s , as s h o w n i n F i g u r e 2 ( 1 7 ) , e v e n parts p e r m i l l i o n of i r o n i n p a l l a d i u m m a y b e n o t i c e d r e a d i l y i n s u s c e p t i b i l i t y measurements

at l o w temperatures.

N e u t r o n scattering

measurements h a v e s h o w n that i r o n i m p u r i t i e s h a v e a n effect f a r b e y o n d the n e a r e s t - n e i g h b o r p a l l a d i u m atoms, e x t e n d i n g p e r h a p s to t h e nearest 100 p a l l a d i u m atoms, a c c o u n t i n g f o r the extreme s e n s i t i v i t y of p a l l a d i u m to i r o n i m p u r i t i e s

(28).

P l a t i n u m , F i g u r e 3 (17), shows b e h a v i o r s i m i l a r t o t h a t of p a l l a d i u m b u t its s u s c e p t i b i l i t y a n d the effect of i r o n i m p u r i t i e s are m u c h s m a l l e r . T h e s m a l l p e a k at 100°Κ is analogous to that f o r p a l l a d i u m .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

4

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

Local Moments C o n s i d e r a b l e research i n recent years has b e e n c a r r i e d o u t o n the m a g n e t i c properties of alloys of elements of the s e c o n d a n d t h i r d l o n g r o w s of the p e r i o d i c table w i t h s m a l l amounts of elements i n the

first

l o n g r o w . S o m e of the most i n t e r e s t i n g results of this w o r k are c e n t e r e d o n t h e p l a t i n u m metals. O n e aspect of the results is g i v e n i n F i g u r e 4

(11),

s h o w i n g the m a g n e t i c m o m e n t of a n i r o n a t o m d i s s o l v e d i n the s e c o n d r o w t r a n s i t i o n metals. A n e n h a n c e m e n t of the i r o n m o m e n t is a p p a r e n t for alloys w i t h electron concentrations of a b o u t 5.5 to 7 a n d 8.25 to 9. F o r electron concentrations f r o m 9 to 10.25 there is a v e r y l a r g e e n h a n c e ­ m e n t , the m o m e n t e x c e e d i n g t h a t of i r o n i n its b u l k state ( a b o u t 2.2

μ ). Β

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

A l l o y s s h o w i n g this large e n h a n c e m e n t are r e g a r d e d as h a v i n g " g i a n t moments."

E n h a n c e m e n t effects of the solute m o m e n t h a v e b e e n f o u n d

i n m a n y a l l o y systems, i n c l u d i n g C r (2), C o (9, 10, 38)

M n (2),

F e (10,

11, 18),

and

i n p a l l a d i u m a n d alloys of p a l l a d i u m a n d r h o d i u m . T h e

e x p e r i m e n t a l t e c h n i q u e w i d e l y u s e d to s h o w the existence of s u c h l o c a l m o m e n t s is the m e a s u r e m e n t of s u s c e p t i b i l i t y . T h e s u s c e p t i b i l i t y is m e a ­ s u r e d as a f u n c t i o n of t e m p e r a t u r e , u s u a l l y f r o m 1.4° Κ to r o o m t e m p e r a ­ ture or higher.

T h e d a t a f r o m alloys w i t h

a

temperature-dependent

s u s c e p t i b i l i t y are fitted to a C u r i e - W e i s s t y p e of c u r v e w h i c h leads to 14

3

4

Y

Zr

5

6

Nb

7

Mo

Re

ELECTRON

8

9

10

11

Ru

Rh

Pd

Ag

Ν

CONCENTRATION

Physical Review

Figure 4. iron atom metals and and alloy)

Magnetic moment in Bohr magnetons of an dissolved in various second row transition alloys {one atomic per cent iron in each metal as a function of electron concentration (11)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

1.

A L B E R T

A N D RUBIN

Os . I o.e 0

4

r

Magnetic

I

5

Properties

r

COMPOSITION

p

(ATOMIC

P E R

t

C E N T )

Journal of Applied

Physics

Figure 5. Susceptibility per mole for alloys containing one atomic per cent iron at 3 different temperatures (18) the i n t e r p r e t a t i o n that a l o c a l m o m e n t exists o n the solute a t o m a n d p e r mits the c a l c u l a t i o n of the m o m e n t associated w i t h the a l l o y . A l l o y s of i r i d i u m a n d p l a t i n u m w i t h s i m i l a r s m a l l amounts of i r o n also e x h i b i t e n h a n c e m e n t effects a n d a giant m o m e n t i n the case of i r o n i n p l a t i n u m a n d p l a t i n u m - r i c h alloys as s h o w n i n F i g u r e 5

(18).

It is o b v i o u s that, i n v i e w of the l a r g e m e a s u r e d m o m e n t s o n the solute atoms, there is m o r e i n v o l v e d t h a n s i m p l y the m a g n e t i c

moment

of the solute a t o m . T h e postulate most w i d e l y u s e d suggests a m o d e l i n w h i c h the m o m e n t o n the solute atoms interacts w i t h the m a g n e t i c m o ments o n the i t i n e r a n t 4d or 5d electrons of the host m e t a l . T h i s i n t e r a c t i o n p r o d u c e s a p o l a r i z a t i o n of the spins i n the 4d or 5d b a n d , at t h e same t i m e a l i g n i n g the l o c a l i z e d m o m e n t s on the solute atoms i n the same d i r e c t i o n as the p o l a r i z e d d-electrons.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

U s i n g this l o c a l m o m e n t m o d e l , a n d u s i n g b a n d t h e o r y or its v a r i a tions, a n u m b e r of w o r k e r s h a v e b e e n a b l e to f o r m u l a t e expressions w h i c h represent the m e a s u r e d m a g n e t i c d a t a r e a s o n a b l y w e l l , at least for the case w h e r e w e l l - l o c a l i z e d m o m e n t s are d e v e l o p e d o n the solute atoms (11,

18).

H o w e v e r , c o n s i d e r a b l y m o r e d a t a has b e c o m e a v a i l a b l e o n

o t h e r properties of d i l u t e a l l o y s , i n c l u d i n g d a t a o n resistivity a n d specific heat, n e u t r o n scattering, v a r i o u s m a g n e t i c resonance experiments, M o s s b a u e r measurements, K o n d o effect,

a n d the l i k e .

Measurements have

b e e n e x t e n d e d also to alloys of m a n y other systems besides those i n v o l v -

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

i n g the p l a t i n u m metals.

Journal of Applied Physics

Figure 6. ceptibility,

(a) Magnetization (at 5 KOe) and inverse initial sus(b) Electrical resistivity of ordered FeRh for increasing (%) and decreasing (O) temperature (25)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

A N D

R U B I N

Magnetic

7

Properties

T h e scope of this r e v i e w p r e c l u d e s a d e s c r i p t i o n of these d a t a , b u t the results of some of these experiments h a v e s h o w n weaknesses i n t h e o r i g i n a l b a n d m o d e l a p p r o a c h (9, 20, 34). ments (21,

22, 26)

H o w e v e r , n e w e r t h e o r e t i c a l treat-

are p r o v i d i n g m o r e i n s i g h t i n t o the p r o b l e m .

The

subject of l o c a l i z e d m a g n e t i c states i n d i l u t e m a g n e t i c alloys is s t i l l i n a state of v e r y a c t i v e r e s e a r c h a n d t h e o r e t i c a l d e v e l o p m e n t , as s h o w n b y the p r o g r a m s of e v e n the most recent m a g n e t i c conferences, s u c h as the Fifteenth A n n u a l Conference

on Magnetism and Magnetic Materials,

P h i l a d e l p h i a , P a . , N o v e m b e r 1969.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

Ordered Alloys I n a d d i t i o n to the d i l u t e alloys a l r e a d y discussed, there are a n u m b e r of alloys of the metals of the p l a t i n u m g r o u p w i t h manganese,

iron,

cobalt, a n d n i c k e l w h i c h have m a g n e t i c properties b a s e d o n t h e f o r m a t i o n of o r d e r e d structures at some p a r t i c u l a r c o m p o s i t i o n . C o n s i d e r i n g i r o n alloys first, the i r o n - r h o d i u m system is a n interesti n g e x a m p l e of m a g n e t i c o r d e r i n g . E a r l y m a g n e t i c measurements i n the system (16)

established that alloys of a b o u t 50 a t o m i c %

rhodium in-

creased i n m a g n e t i z a t i o n as t h e i r t e m p e r a t u r e was r a i s e d t h r o u g h a c r i t i c a l v a l u e . Since 1960, a n u m b e r of w o r k e r s (23, 25, 36) change is o w i n g to a

first-order

h a v e s h o w n t h a t this

a n t i f e r r o m a g n e t i c ( A F M ) to f e r r o m a g -

n e t i c ( F M ) t r a n s i t i o n w i t h i n c r e a s i n g t e m p e r a t u r e , the t r a n s i t i o n t e m p e r a t u r e for a 52 a t o m i c % Figure 6 (25).

r h o d i u m b e i n g a b o u t 350°K, as s h o w n i n

X - r a y d i f f r a c t i o n studies h a v e s h o w n that the c r y s t a l

structure a b o v e a n d b e l o w the t r a n s i t i o n t e m p e r a t u r e is a n o r d e r e d C s C l type, the t r a n s i t i o n b e i n g a u n i f o r m r a p i d v o l u m e e x p a n s i o n of about 1 % w i t h increasing temperature.

C h a n g e s i n l a t t i c e d i m e n s i o n s i n this t y p e

of t r a n s f o r m a t i o n r e s u l t f r o m the differences b e t w e e n the magnetoelastic expansion of the f e r r o m a g n e t i c a l l y o r d e r e d lattice a n d the c o n t r a c t i o n o w i n g to the a n t i f e r r o m a g n e t i c lattice. M e a s u r e m e n t s of the l o w - t e m p e r a t u r e specific heat of i r o n - r h o d i u m alloys a n d i r o n - r h o d i u m - p a l l a d i u m alloys a n d of e n t r o p y changes of the t r a n s i t i o n h a v e s h o w n that the difference i n t h e energies of the F M a n d A F M state is r e l a t i v e l y s m a l l . T h i s suggests a m o d e l i n w h i c h b e l o w the t r a n s i t i o n t e m p e r a t u r e i n the A F M state, r h o d i u m atoms, b y s y m m e t r y , h a v e no net field

exchange

exerted b y the i r o n atoms a n d the energy is d o m i n a t e d b y

iron-

i r o n interactions. A b o v e the t r a n s i t i o n t e m p e r a t u r e , i n the F M state, the r h o d i u m atoms are p o l a r i z e d b y a n exchange field w h i c h i n d u c e s a s i g nificant l o c a l m o m e n t o n the r h o d i u m atoms.

This introduces

another

e n e r g y t e r m w h i c h , i f the s u s c e p t i b i l i t y of the r h o d i u m atoms is l a r g e e n o u g h , w i l l a c c o u n t for the c h a n g e to the F M state (-23).

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

P L A T I N U M

300

GROUP

M E T A L S

A N D

C O M P O U N D S

400 Τ (°K) Journal of Applied

Figure

7.

Magnetization in a 12.5 KOe field of FeRh line is for the bulk alloys (27).

filings.

Physics

The dashed

A n i n t e r e s t i n g effect i n i r o n - r h o d i u m alloys is n o t e d i n c o l d - w o r k i n g the a l l o y . F i l i n g a n a l l o y to m a k e p o w d e r is a c o n v e n i e n t w a y of c o l d w o r k i n g . M a g n e t i c measurements o n filings are s h o w n i n F i g u r e 7

(27).

S t a r t i n g at p o i n t A , the a l l o y is c o o l e d o 7 0 ° K a n d t h e n h e a t e d to 500°K. l

I t is e v i d e n t t h a t i n the c o l d - w o r k e d a l l o y there is no trace of the A F M to F M t r a n s i t i o n i n this range. B e t w e e n 500° to 700 ° C , a n o r m a l C u r i e p o i n t b e h a v i o r emerges a n d , o n c o o l i n g , the reappears.

first-order

transformation

X - r a y d i f f r a c t i o n measurements o n the filings i n d i c a t e d t h a t

i n the as-filed c o n d i t i o n the filings h a v e a d i s o r d e r e d fee structure, b u t q u e n c h i n g f r o m temperatures as h i g h as 1 4 0 0 ° C d i d not result i n the a p p e a r a n c e of the fee structure. F i r s t - o r d e r transitions also exist for the compositions P t F e , b a s e d o n the C u A u - t y p e structure. 3

3

P d F e and 3

I n the o r d e r e d state, the

f o r m e r a l l o y is f e r r o m a g n e t i c a n d the latter is a n t i f e r r o m a g n e t i c .

Inter­

m e d i a t e compositions b a s e d o n F e ( P d , P t ) h a v e s h o w n the existence of 3

a state at l o w temperatures i n w h i c h , s t i l l b a s e d o n the o r d e r e d C u A u 3

structure, the i r o n m o m e n t s m o v e i n t o a " c a n t e d " s t r u c t u r e as s h o w n i n F i g u r e 8 (24).

F o r the c o m p o s i t i o n F e P d i . P t i . , the t r a n s i t i o n f r o m a 6

4

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

Magnetic

A N D R U B I N

9

Properties

s i m p l e f e r r o m a g n e t i c state to this f e r r i m a g n e t i c state w i t h c a n t e d i r o n m o m e n t s occurs at a b o u t 140 °K. T h e a l l o y P t F e w i t h a d d e d i r o n is a n i n t e r e s t i n g case b y itself ( 1 ). 3

T h e o r d e r e d a l l o y is a n t i f e r r o m a g n e t i c w i t h f e r r o m a g n e t i c sheets of i r o n atoms a r r a n g e d o n ( 1 1 0 )

planes a n t i f e r r o m a g n e t i c a l l y a l o n g the

[001]

axis. A s the i r o n content is i n c r e a s e d over the s t o i c h i o m e t r i c 25 a t o m i c % , a different A F M structure appears w i t h the sheets a r r a n g e d o n ( 100 ) planes. A t 30 a t o m i c % i r o n , this structure p r e d o m i n a t e s . B e t w e e n these t w o extremes, b o t h types of s t r u c t u r e coexist.

F r o m neutron diffraction

e x p e r i m e n t s , i t is c o n c l u d e d t h a t phase coherence of the t w o structures occurs o v e r m a n y u n i t cells a n d t h a t there is a n i n t e r t w i n i n g of t h e t w o structures r a t h e r t h a n s e p a r a t i o n i n t o d o m a i n s

of

one

or

the

other

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

structure. T h e platinum—cobalt system is e s p e c i a l l y i m p o r t a n t i n that i t has the o n l y p r e c i o u s m e t a l a l l o y ever to b e d e v e l o p e d f o r p r a c t i c a l use of its m a g n e t i c p r o p e r t i e s . stoichiometric P t C o .

T h i s a l l o y is b a s e d o n s t o i c h i o m e t r i c or n e a r -

It is d i s t i n g u i s h e d b y a v e r y h i g h - e n e r g y p r o d u c t ,

a r e l a t i v e l y l o w r e m a n e n c e , a n d h i g h c o e r c i v i t y . F i e l d s of 30,000 oersteds or h i g h e r are r e q u i r e d for s a t u r a t i o n a n d P t C o magnets are r e g u l a r l y p r o d u c e d w i t h e n e r g y p r o d u c t s greater t h a n 9 m i l l i o n

gauss-oersteds,

coercive forces of 4300 oersteds, a n d r e m a n e n c e near 6400 gauss.

•

Fe

°Pd,Pt Journal of Applied

Figure

8.

Low-temperature canted-ferrimagnetic ofFePd^Pt^ (24)

Physics

structure

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

FePt

10

P L A T I N U M

DISORDERED

CUBIC

GROUP

M E T A L S

ORDERED

{ll0}

c

A N D

C O M P O U N D S

TETRAGONAL

II ( I O I ) t

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

C

Figure

9.

Crystallographic relationships disordered and ordered PtCo

between

is i s o m o r p h o u s to P t C o a n d p r e s u m a b l y shares m a g n e t i c h a r d e n i n g m e c h anisms. It has never b e e n u s e d p r a c t i c a l l y because

its c o e r c i v i t y a n d

e n e r g y p r o d u c t s are l o w e r t h a n those of P t C o . P t C o is a n o r d e r i n g a l l o y , f o r m i n g a f a c e - c e n t e r e d - t e t r a g o n a l t y p e structure (c/a tice (31).

CuAu-

— 0.98) f r o m a d i s o r d e r e d face-centered c u b i c l a t -

M a x i m u m c o e r c i v e force a n d m a x i m u m energy p r o d u c t are

a c h i e v e d at less t h a n c o m p l e t e o r d e r , a n d at different stages i n the a p p r o a c h to c o m p l e t e order.

O r d e r i n g starts i n the d i s o r d e r e d a l l o y w i t h

the f o r m a t i o n of a system of o r d e r e d platelets, e a c h c o n t a i n i n g a tetrag o n a l c-axis p a r a l l e l to one of the o r i g i n a l o r t h o g o n a l c u b e axes. are (110)

These

platelets; that is, they are not p a r a l l e l to the " c u b e faces" i n

the d i s o r d e r e d m a t e r i a l . I n a n y g i v e n r e g i o n , p r i m a r i l y as a n a c c o m m o d a t i o n to s t r a i n , o n l y t w o of the three possible p l a t e l e t orientations o c c u r F i g u r e 9 s u m m a r i z e s the c r y s t a l l o g r a p h i c aspects of t h i s system.

(8).

E l e c t r o n m i c r o s c o p i c a n d field i o n m i c r o s c o p i c w o r k has s h o w n t h a t m a x i m u m c o e r c i v i t y is a c h i e v e d i n the t e t r a g o n a l phase w i t h p l a t e l e t w i d t h of 2 0 0 - 5 0 0 angstroms a n d w i t h p l a t e l e t thickness of a b o u t 20 angstroms (30, 33).

T h e d i r e c t i o n of easy m a g n e t i z a t i o n ( c - a x i s ) is n o t i n the p l a n e of

the platelet. T h e degree of t r a n s f o r m a t i o n is f a r f r o m c o m p l e t e at m a x i m u m p r o p e r t i e s , p e r h a p s as little as 5 0 % t r a n s f o r m a t i o n b y v o l u m e

(32).

T h e s a t u r a t i o n m a g n e t i z a t i o n of the d i s o r d e r e d a l l o y is 43.5 gauss c m / g m at 30,000 oersteds (14). 3

T h e m a x i m u m internal magnetization

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

320

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

Magnetic

A N D R U B I N

220

11

Properties

340

0

20

40

200

180

160

f+0

Engelhard Industries Technical Bulletin

Figure 10.

Magnetic anisotropy in a PtCo single crystal (37)

Journal

of Applied

Physics

Figure 11. Crystallite distribution in ordered PtCo (8)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

12

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

of the o r d e r e d phase has b e e n estimated as 3 5 - 4 0 % l o w e r t h a n t h a t of the d i s o r d e r e d phase (14).

T h e average m a g n e t i c m o m e n t o f d i s o r d e r e d

P t C o at r o o m t e m p e r a t u r e is 1.04 b o h r magnetons w i t h a s p h e r i c a l d i s t r i b u t i o n of m o m e n t ( 8 ) .

T h e easy m a g n e t i z a t i o n d i r e c t i o n i n the or-

d e r e d phase corresponds

to its c-axis a n d the a n i s o t r o p y constant is

a p p r o x i m a t e l y 50 m i l l i o n e r g / c m

3

(8).

S i n g l e - c r y s t a l w o r k b y W a l m e r (37)

(on a fully-ordered crystal)

s h o w e d a m a x i m u m of the coercive force i n the 111 d i r e c t i o n a n d m i n i m a i n the 110 a n d 100 d i r e c t i o n s , the 100 m i n i m u m b e i n g the l o w e r of t h e t w o (Figure 10).

W o r k b y Brissonneau a n d coworkers (8)

o n the d i s t r i b u -

t i o n of platelets i n c o m p l e t e l y - o r d e r e d P t C o has l e d to a m o d e l s h o w n i n F i g u r e 11, w h e r e i n e a c h z o n e s h o w n i n the figure contains a f u l l y Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

d e v e l o p e d n e t w o r k of ( 110) platelets o r i e n t e d i n t w o of the three p o s s i b l e orthogonal directions. T h e z o n e m o d e l p r o p o s e d b y B r i s s o n n e a u is consistent n o t o n l y w i t h his o w n field i o n m i c r o s c o p i c observations, b u t also w i t h l a r g e r scale a n d often p u z z l i n g p h e n o m e n a observed.

P t C o magnets, for instance, f o r m

B i t t e r patterns o n a scale q u i t e easily v i s i b l e u n d e r a l i g h t m i c r o s c o p e . B i t t e r patterns d o not fit the p i c t u r e of a " f i n e - p a r t i c l e " h a r d e n i n g m e c h a n i s m unless t h e y also d e s c r i b e a l a r g e r scale p h e n o m e n o n , s u c h as B r i s sonneau zone boundaries. B e c a u s e of the s e n s i t i v i t y of the platelets to strain energy, t h e i r n u c l e a t i o n s h o u l d be sensitive to the w o r k i n g h i s t o r y of the b i l l e t s f r o m w h i c h the a l l o y s p e c i m e n is m a d e , a n d , n o t s u r p r i s i n g l y , P t C o responds w e l l to c o l d w o r k i n g b e f o r e heat t r e a t i n g . W o r k b y S h i m i z u a n d H a s h i m o t o (35),

w h o t e m p e r e d P t C o u n d e r elastic stress f a r b e l o w its elastic

l i m i t , has s h o w n that the a l l o y develops

considerably lower coercivity

Journal of Applied

Physics

Figure 12. Effects of compressive and tensile stresses on PtCo hysteresis curves (35)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

Magnetic

A N D RUBIN

Δ

MRu

2

RARE-EARTH

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

13

Properties

ELEMENT

I NM R U

2

, M 0S2t Μ ΐ Γ

2

Physical Review

Figure

13. Curie temperatures for MX compounds (M = rare earth, X = Ru, Os, or Ir) (7) 2

( a n d higher remanence)

i n the direction of the a p p l i e d

compressive

stress t h a n at r i g h t angles to i t ( F i g u r e 1 2 ) . T h e y also r e p o r t t h e c o n ­ verse to b e true w h e n tensile stress is a p p l i e d .

Platinum Metal—Rare Earth Alloys T h e m a g n e t i c m o m e n t s o f rare e a r t h elements a r e c a u s e d b y t h e u n p a i r e d electrons i n t h e i r 4f shells. T h e s e shells" are s h i e l d e d b y t h e outer shells so t h a t c h e m i c a l b o n d i n g h a s r e l a t i v e l y l i t t l e effect o n t h e m a g n e t i c m o m e n t s o f these elements. L a v e s phases o f c o m p o s i t i o n M B

2

T h e rare earths f o r m a series o f

( M = rare e a r t h , Β == p r e c i o u s m e t a l )

w h i c h share t h e c h a r a c t e r i s t i c of f e r r o m a g n e t i c c o u p l i n g a t l o w t e m p e r a ­ tures ( 7 ) . F i g u r e 13 shows t h e C u r i e t e m p e r a t u r e s o f a series o f corn-

Table II.

Θ, °K

Compound PrRu PrRh PrOs Prlr PrPt GdRh Gdlr GdPt

40 8.6 >35 18.5 7.9 >77 >77 >77

2 2

2

2

2

2

2

2

° Reprinted from

Ferromagnetic Curie Points

Acta

Crystallographica

a

Compound

Θ, °K

NdRu NdRh Ndlr NdPt

35 8.1 11.8 6.7

2 2

2

2

{12).

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

14

P L A T I N U M

-12

-8 -4 H, MAGNETIC

GROUP

0 F I E L D IN

M E T A L S

A N D

4 8 KILO-OERSTEDS

C O M P O U N D S

12

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

(a)

-8

-4

0

4

H, MAGNETIC FIELD IN

8

ΚILO - OERSTEDS

(b) Journal of Applied Physics

Figure 14. Hysteresis loops for 2 GdRu -CeRu ing (a) superconductivity and ferromagnetism, ductivity alone (4) 2

pounds where Β = MgCu

2

2

alloys show­ (b) supercon­

R u , O s , a n d I r . T h e s e c o m p o u n d s f o r m i n the c u b i c

( C 1 5 ) o r the h e x a g o n a l M g Z n

2

( C 1 4 ) structures ( 7 ) .

The Curie

p o i n t is h i g h e s t w i t h c o m p o u n d s c o n t a i n i n g G d a n d decreases w i t h l a r g e r o r s m a l l e r a t o m i c n u m b e r s of the r a r e earths ( F i g u r e 1 3 ) . S i m i l a r results have been obtained w i t h Β =

R h or P t (12)

(Table II).

The variation

i n C u r i e temperatures results p r i n c i p a l l y f r o m the i n t e r a c t i o n b e t w e e n the spins of the 4f shells of the rare earths a n d the c o n d u c t i o n electrons. P s e u d o b i n a r y alloys of ( C e R u - G d R u ) (4), 2

(GdRu^ThRujî)

(6),

(GdOs -LaOs ) 2

2

2

(5),

(YOs -GdOs ) 2

2

(29),

a n d p e r h a p s some others

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1.

A L B E R T

A N D

Magnetic

R U B I N

15

Properties

s h o w s i m u l t a n e o u s f e r r o m a g n e t i c a n d s u p e r c o n d u c t i n g p r o p e r t i e s over a l i m i t e d range of c o m p o s i t i o n .

T h e system G d R u

2

in CeRu

2

has

been

s t u d i e d extensively. T h i s system shows a s u p e r c o n d u c t i n g t r a n s i t i o n w h e n the c o n c e n t r a t i o n of G d R u more than 6 %

GdRu

2

2

is less t h a n 10 a t o m i c % .

c r e a s i n g w i t h c o n c e n t r a t i o n (4). 8 and 4 % G d R u

2

Alloys containing

are f e r r o m a g n e t i c w i t h C u r i e t e m p e r a t u r e s i n ­ F i g u r e 14 shows hysteresis loops

for

a l l o y s , the latter b e i n g s u p e r c o n d u c t i n g a n d the f o r m e r

being simultaneously superconducting and ferromagnetic.

Both

loops

s h o w the e x c l u s i o n of field c h a r a c t e r i s t i c of s u p e r c o n d u c t i n g m a t e r i a l s ,

Table III.

Curie Temperature and Coercive Force of R s P d Compounds (3)

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

2

Θ, °K

Compound Gd Pd 6

Hc(at

4.2°K)oe

335

2

Tb5.10Pd1.90

~30

12,800

Dy5.07Pd1.93

~25

9,700

H o . o P d i •96

~10

1,300

5

4

i.e., n e g a t i v e slope o n i n i t i a l m a g n e t i z a t i o n a n d n e g a t i v e s l o p e n e a r r e m a ­ nence i n the first q u a d r a n t . T h e n o r m a l or n o n f e r r o m a g n e t i c s u p e r c o n ­ d u c t o r exhibits a " r e m a n e n c e " a t t r i b u t e d to " f r o z e n - i n " flux. T h e m a g ­ n e t i z a t i o n c u r v e for the f e r r o m a g n e t i c ( 8 % )

a l l o y lies w e l l a b o v e that

c a l c u l a t e d for a p a r a m a g n e t i c m a t e r i a l of the same G d content, a n d the r e m a n e n c e is also w e l l a b o v e that e x p e c t e d for a p a r a m a g n e t i c s u p e r ­ conductor.

I t is q u e s t i o n a b l e w h e t h e r s u p e r c o n d u c t i v i t y a n d f e r r o m a g -

n e t i s m exist i n the same d o m a i n s i n a g i v e n s p e c i m e n .

T h e minor loop

P Q R S shows t h a t some s u p e r c o n d u c t i v i t y s t i l l exists i n parts of the a l l o y after s u p e r c o n d u c t i v i t y as a w h o l e has b e e n d e s t r o y e d . C o m p o u n d s of n o m i n a l c o m p o s i t i o n Μ Β , w h e r e M is a g a i n a r a r e δ

2

earth ( G d , T b , H o , D y ) a n d Β a precious m e t a l (Pt, P d ) , show m a g ­ netizations close to those c a l c u l a t e d f r o m t h e m o m e n t s of the r a r e e a r t h atoms

(3).

Gd Pd 5

2

is a soft m a g n e t i c m a t e r i a l w i t h a c o e r c i v e

force

less t h a n 100 oersteds b u t w i t h a h i g h s a t u r a t i o n associated w i t h the h i g h m o m e n t of G d ( 3 ) .

T a b l e I I I s u m m a r i z e s the p e r m a n e n t m a g n e t i c p r o p ­

erties of the p a l l a d i u m alloys. T h e p l a t i n u m alloys are i s o s t r u c t u r a l a n d h a v e t h e same C u r i e t e m p e r a t u r e s ( 19).

E n e r g y p r o d u c t s for T b P d a n d

D y P d at 4.2°K are 20 X

1 0 gauss-oersteds, r e s p e c t i v e l y

5

(3).

1 0 a n d 26 X 6

5

6

W h i l e these e n e r g y p r o d u c t s are h i g h e r t h a n p l a t i n u m - c o b a l t , the

l o w C u r i e t e m p e r a t u r e s p r e c l u d e use of these c o m p o u n d s

i n the u s u a l

platinum-cobalt applications.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch001

16

PLATINUM GROUP METALS AND COMPOUNDS

Literature Cited (1) Bacon, G. E., Crangle, J., Proc. Roy. Soc. 1963, A272, 387. (2) Barton, E. E., Claus, H., private communication. (3) Berkowitz, A. E., Holtzberg, F., Methfessel, S.,J.Appl. Phys. 1964, 35, 1030. (4) Bozorth, R. M., Davis, D. D., J. Appl. Phys. 1960, 31, 321S. (5) Bozorth, R. M., Davis, D. D., Williams, A. J., Phys. Rev. 1960, 119, 1570. (6) Bozorth, R. M., Matthias, B. T., Davis, D. D., Proc. Intern. Conf. Low Temp. Phys., 7th, Toronto, Canada, 1960, 1961, p. 385. (7) Bozorth, R. M., Matthias, B. T., Suhl, H., Corenzwit, E., Davis, D. D., Phys. Rev. 1959, 115, 1595. (8) Brissonneau, P., Blanchard, Α., Schlenker, M., Laugier, J., J. Appl. Phys. 1969, 39, 1266. (9) Brog, K.C.,Jones, W. H., Booth, J. G.,J.Appl.Phys. 1967, 38, 1151. (10) Cape, J. Α., Hake, R. R., Phys. Rev. 1965, 139, A142. (11) Clogston, A. M.,etal.,Phys. Rev. 1962, 125, 541. (12) Compton, V. B., Matthias, B. T., Acta Cryst. 1959, 12, 651. (13) Doclo, R., Foner, S., Narath, Α.,J.Appl.Phys. 1969, 40, 1206. (14) Dunaev, F. N., Kalinin, V. M., Kryokov, I. P., Maisinovich, V. I., Fiz. Metal i Metaloved. 1965, 20, 460. (15) Engelhard Ind. Tech.Bull.VI, No. 3, December, 1965. (16) Fallot, M., Hocart, R., Rev. Sci. 1939, 77, 498. (17) Foner, S., Doclo, R., McNiff, E. J., Jr.,J.Appl.Phys. 1968, 39, 551. (18) Geballe, T. H.,etal.,J.Appl.Phys. 1965, 37, 1181. (19) Holtzberg, F., Methfessel, S. J., U. S. Patent 3,326,637 (1967). (20) Knapp, G. S.,J.Appl.Phys. 1967, 38, 1267. (21) Knapp, G. S., Phys. Letters 1967, 25A, 114. (22) Kondo, J., Phys. Rev. 1968, 169, 437. (23) Kouvel, J. S.,J.Appl.Phys. 1966, 37, 1257. (24) Kouvel, J. S., Forsyth, J. B.,J.Appl.Phys. 1969, 40, 1359. (25) Kouvel, J. S., Hartelius, C.C.,J.Appl.Phys. 1962, 33, 1343. (26) Lederer, P., Mills, D. L., Phys. Rev. 1968, 165, 837. (27) Lommel, J. M., Kouvel, J. S.,J.Appl. Phys. 1967, 38, 1263. (28) Low, G. G., Holden, T. M., Proc. Phys. Soc. 1966, 89, 119. (29) Matthias, B. T., U. S. Patent 2,970,961 (1961). (30) Mishin, D. D., Greshishkin, R. M., Phys. Status Solidi 1967, 19, K1-K3. (31) Newkirk, J. B., Geisler, A. H., Martin, D. L., Smoluchowski, R.,J.Metals 1950, 188, 1249. (32) Rabinkin, A. G., Tyapkin, Yu. D., Yamaleev, Κ. M., Fiz. Metal i Metaloved. 1965, 19, 360. (33) Ralph, B., Brandon, D. G., Proc. European Conf. Electron Microsco 3rd, Prague 1964 (A) 303. (34) Sarachik, M. P., Phys. Rev. 1968, 170, 679. (35) Shimizu, S., Hashimoto, E.,J.Appl. Phys. 1968, 39, 2369. (36) Tu, P.,etal.,J. Appl. Phys. 1969, 40, 1368. (37) Walmer, M. L., Engelhard Ind. Tech.Bull.1962, 2, 117. (38) Walstedt, R. E., Sherwood, R.C.,Wernicke, J. H., J. Appl. Phys. 1968, 39, 555. (39) Weiss, R. J., "Solid State Physics for Metallurgists," p. 323, Pergamon, New York, 1963. RECEIVED January 16, 1970.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

Platinum Metal Chalcogenides

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

AARON WOLD Brown University, Providence, R. I. 02912

A number of binary platinum metal chalcogenides show interesting electrical and magnetic properties. These are classified according to structure types and their properties related to the formal valence of the platinum metal. A simple one-electron model proposed by Goodenough to explain the properties of the first row transition metal chal cogenides can be applied to the corresponding platinum metal compounds. This theory is successful in correlating new experimental data on these compounds—e.g., crysta structure, resistivity, Seebeck coefficient, and magnetic susceptibility. *"phe electrical and magnetic properties of simple binary platinum metal oxides (15, 19), as well as a number of ternary compounds (4), have shown that these materials can be of considerable interest to both solid state chemists and physicists. A number of the platinum metal oxides are remarkably good electrical conductors and, in addition, magnetic ordering has been observed (4) for several perovskites containing ruthenium. Many of these compounds can be prepared in the form of single crystals (IS), making them suitable for both transport and magnetic measurements. The platinum metal chalcogenides in general are easier to prepare than the corresponding oxides. Whereas special conditions of temperature and pressure are required to prepare many of the oxides, the platinum metals react most readily with S, Se, and Te. A number of additional differences concerning the chemistry of the chalcogenides and the oxides are summarized as follows: The metal-sulfur (selenium, tellurium) bond has considerably more covalent character than the metal-oxygen bond and, therefore, there are important differences in the structure types of the compounds formed. Whereas there may be considerable similarity between oxides andfluorides,the structural chemistry of the sulfides tends to be more closely related to that of the chlorides. The latter compounds 17 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

18

P L A T I N U M

GROUP

M E T A L S

A N D

C O M P O U N D S

f o r m as p r i m a r i l y l a y e r - t y p e structures, a n d a n u m b e r of i m p o r t a n t s t r u c ­ t u r e types are f o u n d i n sulfides that h a v e n o c o u n t e r p a r t a m o n g the o x i d e structures—e.g., p y r i t e , m a r c a s i t e , n i c k e l arsenide. F i n a l l y , m a n y of t h e p l a t i n u m m e t a l c h a l c o g e n i d e s b e h a v e l i k e a l l o y s ; t h e elements d o a p p e a r to h a v e t h e i r n o r m a l valencies a n d , i n a d d i t i o n , the

not

compounds

h a v e a w i d e r a n g e of c o m p o s i t i o n a n d s h o w m e t a l l i c luster, r e f l e c t i v i t y , and conductivity. Goodenough

(10)

has a c c o u n t e d for the m e t a l l i c p r o p e r t i e s of

a

n u m b e r of first r o w t r a n s i t i o n m e t a l c h a l c o g e n i d e s , a n d these ideas are also a p p l i c a b l e to the p l a t i n u m m e t a l chalcogenides.

H e has s h o w n that

t h e f o r m a t i o n of c o n d u c t i o n b a n d s is p o s s i b l e as a result of strong covalent m i x i n g between the cation e

9

a n d a n i o n s,p

a

orbitals. T h i s m i x i n g

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

a l l o w s sufficient i n t e r a c t i o n b e t w e e n o c t a h e d r a l l y c o o r d i n a t e d cations o n opposite sides of a n a n i o n so that the c o n d i t i o n s for l o c a l i z e d d-electrons break down.

T h e r e s u l t i n g d - l i k e c o l l e c t i v e - e l e c t r o n b a n d s , w h i c h are

a n t i b o n d i n g w i t h respect to the a n i o n array, are d e s i g n a t e d σ * b a n d s . M e t a l l i c b e h a v i o r c a n o c c u r w h e n these b a n d s exist a n d are p a r t i a l l y o c c u p i e d b y electrons. M e t a l l i c c o n d u c t i o n m a y o c c u r also i f c o n d u c t i o n b a n d s are f o r m e d b y the d i r e c t o v e r l a p of t r a n s i t i o n m e t a l t

2g

orbitals.

H e r e a g a i n , these b a n d s m u s t b e p a r t i a l l y o c c u p i e d .

et al. (19)

—

t

2g

Rogers

h a v e a p p l i e d the G o o d e n o u g h m o d e l to a c c o u n t for the elec­

t r i c a l b e h a v i o r of a n u m b e r of p l a t i n u m m e t a l oxides.

T h e s e concepts

m a y also b e a p p l i e d to t h e p l a t i n u m m e t a l chalcogenides. It w i l l not b e possible, i n this p a p e r , to d e a l w i t h a l l of the p l a t i n u m m e t a l chalcogenides.

I n s t e a d , a n u m b e r of examples w i l l be c h o s e n a n d

t h e i r e l e c t r i c a l as w e l l as m a g n e t i c p r o p e r t i e s c o r r e l a t e d w i t h the a t o m i c positions i n the v a r i o u s structures f o r m e d . T h e first g r o u p of c o m p o u n d s to b e d i s c u s s e d c r y s t a l l i z e w i t h the p y r i t e structure, w h i c h is s h o w n i n F i g u r e 1.

T h i s s t r u c t u r e is s i m i l a r to the N a C l structure i f w e r e p l a c e

N a b y F e a n d each C I b y an S group. H o w e v e r , the S - S distance w i t h i n 2

R.

Figure 1.

W.

Pyrite structure

G. Wyckoff,

"Crystal Structures," Wiley

(20)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2.

Phtinum

W O L D

Table I.

Metal

19

Chalcogenides

Platinum Metal Compounds with the Pyrite Structure Compounds

Properties

Low Spin RuS , OsS , RhPS, RhPSe,

RuSe , OsSe , RhAsS, RhAsSe, RhAsTe, IrPS, IrAsS, IrPSe, IrAsSe, IrAsTe, N i o . P d o .eAsa, PtAs , PtP„ PtBi RhSe~ , RhS~ , IrS^ , IrSe^ IrTe~ 2

2

2

2

2

2

rf

S =

6

0 Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Metallic Semiconductor Metallic Semiconductor Semiconductor Metallic

RuTe OsTe RhSbS, RhBiS RhSbSe, RhBiSe RhSbTe, RhBiTe IrSbS, IrBiS IrSbSe, IrBiSe IrSbTe, IrBiTe PdAs , PdSb PtSb 2

2

2

2

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

2

3

3

3

RhTe~

3

3

3


RhTe

0

2

2

the S

2

PdSbS, PdBiTe, PtSbTe,

PdAsSe, PtAsS, PtBiTe

Metallic Metallic Metallic

PdBiSe PtSbSe

PdSbSe, PtSbS,

g r o u p is s u c h that e a c h i r o n is s u r r o u n d e d b y a d e f o r m e d a n i o n

o c t a h e d r o n , a n d the anions h a v e three c a t i o n a n d one a n i o n n e i g h b o r s , w h i c h together f o r m a d i s t o r t e d t e t r a h e d r o n . A n u m b e r of

compounds

that c r y s t a l l i z e w i t h the p y r i t e s t r u c t u r e are l i s t e d i n T a b l e I. F o r m a n y of t h e m , the t r a n s i t i o n m e t a l has t h e l o w - s p i n d

state. T h e s e

G

compounds

are s e m i c o n d u c t o r s

because the c o n d u c t i o n b a n d

o r b i t a l s ) is e m p t y .

A n a p p a r e n t e x c e p t i o n is I r T e ~ , w h i c h is r e p o r t e d

(17)

to b e a s u p e r c o n d u c t o r .

( σ * , f o r m e d via

e

g

3

A s one proceeds f r o m s u l f u r to s e l e n i u m

to t e l l u r i u m (as anions i n a n i s o s t r u c t u r a l series of c o m p o u n d s ) there is a n a r r o w i n g of t h e b a n d gap, a n d f o r some series of c o m p o u n d s , t h i s is a c c o m p a n i e d b y a m a r k e d c h a n g e i n the t r a n s p o r t properties. T h e m e t a l l i c properties o b s e r v e d for the d

7

compounds

listed i n

T a b l e I a r e also consistent w i t h t h e G o o d e n o u g h m o d e l . T h e r h o d i u m s e l e n i u m system is of p a r t i c u l a r interest a n d demonstrates c l e a r l y the important

relationships between

structure

and

transport

properties.

C a t i o n s m a y b e r e m o v e d f r o m the s u p e r c o n d u c t i n g c o m p o u n d 6 ° K ) , R h S e . T h e p y r i t e s t r u c t u r e is m a i n t a i n e d as the e

g

2

a l l y e m p t i e d , a n d at t h e c o m p o s i t i o n R h / S e 2

t r i v a l e n t — L e . , h a v e t h e c o n f i g u r a t i o n 4d . 6

3

2

(T

c

=

b a n d is g r a d u ­

( R h S e ) , a l l cations are 3

It is not k n o w n yet i f t h e i d e a l

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

20

P L A T I N U M

composition, R h S e , can be obtained.

GROUP

M E T A L S

A N D

C O M P O U N D S

A h o m o g e n e i t y r a n g e is r e p o r t e d

3

(9) f r o m R h S e i . s t o R h S e . , a n d w e k n o w o n l y t h a t R h S e m u s t b e the 2

7

upper limit. However, R h S

3

and IrSe

3

conducting, a n d stoichiometric R h S e

3

3

are d i a m a g n e t i c (12)

and semi-

should show semiconducting

be-

h a v i o r also. A n o t h e r i n t e r e s t i n g c o m p o u n d is I r S e , w h i c h s h o u l d s h o w m e t a l l i c 2

b e h a v i o r since the I r appears to h a v e a d

7

configuration. H o w e v e r , the

I r S e - t y p e c o m p o u n d s are d i a m a g n e t i c s e m i c o n d u c t o r s , a n d t h e i r s t r u c 2

tures r e s e m b l e t h a t of marcasite. shows h e x a g o n a l c l o s e - p a c k e d o c t a h e d r a l holes

filled.

T h e marcasite s t r u c t u r e i n F i g u r e 2

a n i o n layers w i t h h a l f the layers of the

T h e I r S e structure is s h o w n i n F i g u r e 3, a n d t h e 2

r e l a t i o n s h i p to t h e m a r c a s i t e structure is seen r e a d i l y b y c o m p a r i n g the Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

o c t a h e d r a l chains. ABABACAC.

The IrSe

2

structure evolves f r o m a n a n i o n s t a c k i n g

U n i t s of the m a r c a s i t e structure are s t a c k e d together i n

s u c h a w a y t h a t o n l y h a l f t h e anions f o r m p a i r s , a n d t h e cations are indeed trivalent I r ( I I I ) S e • ( S e ) i 2

/ 2

2

~.

T h e c a t i o n , therefore, a c t u a l l y

F. Hulliger, "Structure and Bonding," Springer-Verlag

Figure 2.

Marcasite

structure (13, p. 94)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

2.

Phtinum

W O L D

Metal

21

Chalcogenides

c F. Hulliger, "Structure and Bonding," Springer-Verlag

Figure 3. has a d

IrSe structure (13, p. 100) 2

configuration consistent w i t h the s e m i c o n d u c t i n g ,

G

diamagnetic

properties o b s e r v e d . T h e structure of P d S e , a n e l o n g a t e d p y r i t e , is s h o w n i n F i g u r e 4. 2

T h e s q u a r e - p l a n a r c o o r d i n a t i o n is a c h i e v e d b y e l o n g a t i n g t h e a n i o n o c t a hedron. levels (d

T h i s decrease i n s y m m e t r y results i n a strong s p l i t t i n g of t h e s t a b i l i z e d r e l a t i v e to d . ),

2

2

g

x

y

2

PdS , PdSSe,

e

2

2

are t h e o n l y k n o w n c o m p o u n d s of this structure t y p e a n d are

diamagnetic

(11)

octahedra i n P d S

2

semiconductors.

When

the d i s t o r t i o n of

is r e d u c e d b y pressure, the s e m i c o n d u c t o r

i n t o a m e t a l b e f o r e a c h a n g e to the p y r i t e structure occurs A number

the

anion

transforms (I).

of p l a t i n u m m e t a l c h a l c o g e n i d e s ( P t S , P t S e , P t S e T e ,

P t T e ) c r y s t a l l i z e i n the C d l 2

9

a n d the 8 d-electrons of p a l l a d i u m

just fill a l l a v a i l a b l e d-levels t h r o u g h the l o w e r d * l e v e l . and PdSe

e

2

2

structure ( F i g u r e 5 ) .

h a l f t h e holes of a h e x a g o n a l c l o s e - p a c k e d

2

T h e cations o c c u p y

a r r a y , s u c h that

e m p t y layers alternate to g i v e a s a n d w i c h - l i k e structure.

filled

The

and

cadmium

atoms are s y m m e t r i c a l l y s u r r o u n d e d b y six h a l o g e n atoms at the corners

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

22

PLATINUM

GROUP

METALS

AND

COMPOUNDS

of a n o c t a h e d r o n , whereas the three c a d m i u m n e i g h b o r s of e a c h h a l o g e n a t o m a l l l i e o n one side of i t . S i n c e there are no b o n d s b e t w e e n l i k e atoms, a tetravalent c a t i o n is n e e d e d to m a k e a C d l - t y p e c h a l c o g e n i d e n o n m e t a l 2

lic—e.g., P t S . N a r r o w i n g of the b a n d g a p is o b s e r v e d f o r this series of 2

p l a t i n u m m e t a l chalcogenides Whereas

PtS

2

and PtSe

2

as one

proceeds f r o m

are s e m i c o n d u c t o r s ,

PtS

2

to

PtTe .

PtSeTe and P t T e

2

2

are

metallic. S e v e r a l p l a t i n u m m e t a l chalcogenides of the t y p e M X c r y s t a l l i z e w i t h the N i A s structure. T h e y i n c l u d e R h S e , R h T e , a n d P d T e . T h i s s t r u c t u r e

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

is s h o w n i n F i g u r e 6. E a c h c a t i o n is c o o r d i n a t e d b y six a n i o n n e i g h b o r s

F. Hulliger, "Structure and Bonding,"

Figure 4.

PdSe

2

Springer-Verlag

structure (13, p. 108)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2.

Platinum

W O L D

Metal

23

Chalcogenides

WL

o

m

χ #:Cd;

Q:I

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

R. C. Evans, "Crystal Chemistry," Cambridge University Press

Figure 5.

Ni As

C d l structure s

(7)

STRUCTURE

Figure 6. Nickel structure

arsenide

at t h e corners o f a d i s t o r t e d o c t a h e d r o n , b u t the six c a t i o n n e i g h b o r s o f a n a n i o n are l o c a t e d at the corners of a t r i g o n a l p r i s m . E a c h c a t i o n also has t w o other c a t i o n n e i g h b o r s o n l y s l i g h t l y m o r e r e m o t e t h a n its a n i o n n e i g h ­ bors.

T h e structure m a y be c o n s i d e r e d a filled C d l

2

structure, w i t h a l l

of the o c t a h e d r a l sites i n the c l o s e - p a c k e d h e x a g o n a l a n i o n s u b l a t t i c e n o w o c c u p i e d b y cations.

A n i n t e r e s t i n g g r o u p of t e r n a r y

compounds

m a y b e f o r m e d i n w h i c h o n e - f o u r t h of the sites are e m p t y .

T h i s latter

structure t y p e w a s s t u d i e d first b y J e l l i n e k (14) as the C r S 3

4

a n d u s u a l l y is d e s i g n a t e d

structure.

J e l l i n e k has p o i n t e d out also t h a t the t e t r a g o n a l structure of c o o p erite, P t S , is r e l a t e d to N i A s . I n d i a m a g n e t i c P t S ( c Z ) , f o u r d-orbitals are 8

d o u b l y o c c u p i e d a n d one is e m p t y . T h e r e f o r e , t w o anions f r o m a h y p o ­ t h e t i c a l o c t a h e d r o n h a v e b e e n r e m o v e d , a n d the c a t i o n is i n a s q u a r e p l a n a r c o o r d i n a t i o n ; the a n i o n is c o o r d i n a t e d b y f o u r cations that f o r m a d e f o r m e d t e t r a h e d r o n . T h e cooperite structure is s h o w n i n F i g u r e 7. T h e r e l a t i o n s h i p b e t w e e n the N i S a n d P t S s t r u c t u r e is s i m i l a r to t h a t b e t w e e n

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

24

PLATINUM

Table II.

System

CrRh Se CoRh Se NiRh Se CrRh Te Rh Te CoRh Te NiRh Te

Monoclinic Monoclinic Monoclinic Monoclinic Monoclinic Trigonal Trigonal

4

2

2

4

4

2

3

4

4

2

4 4

AND

COMPOUNDS

a (±

0.005), A

b (±

6.278 6.269 6.280 6.841 6.812 3.953 3.966

0.005), A 3.612 3.644 3.648 3.951 3.954

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

2

METALS

Room-Temperature Structural and Electrical

Compound 2

GROUP

F. Hulliger, "Structure and Bonding," Springer-Verlag

Figure 7.

Cooperite (PtS) structure (13, p. 166)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2.

Phtinum

W O L D

Metal

Data for Ternary Rhodium

c (±

Electrical Resistivity, Ohm-Cm

11.25 10.81 10.82 11.40 11.23 5.429 5.457 NiS

2

Chalcogenides

A

000.5),

1 x

92.47 92.15 92.22 91.61 92.55

io-

3

— 5 X IO" 1 χ io1 x io-

— —

and PdS .

25

Chalcogenides

4 3 4

— 3 X IO"

4

T h e r e is a n e l o n g a t i o n of the a n i o n o c t a h e d r a

2

c h a n g e f r o m a h i g h - s p i n to a d i a m a g n e t i c l o w - s p i n state for the d Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

8

and a cations.

I n a d d i t i o n to t h e s i m p l e b i n a r y p l a t i n u m m e t a l c h a l c o g e n i d e s , w h i c h w e have chosen only a few

ternary compounds have been prepared.

B l a s s e ( 2 , 3 ) has r e p o r t e d t h e

p r e p a r a t i o n a n d properties of several r h o d i u m thiospinels. compound,

CuRh S , 2

shows a w e a k ,

4

p a r a m a g n e t i s m of 320 Χ

10"

6

of

examples, a n u m b e r of i n t e r e s t i n g

nearly

emu/g-mole.

t o r t e d c u b i c s p i n e l , i n d i c a t i n g t h a t the C u

2 +

The copper

temperature-independent

T h e structure is a n u n d i s o n t h e t e t r a h e d r a l site does

not s h o w its u s u a l t e n d e n c y to distort to l o w e r s y m m e t r y via a J a h n - T e l l e r mechanism.

A c c o r d i n g to the G o o d e n o u g h

e x p e c t e d for C u R h S 2

4

m o d e l , these p r o p e r t i e s

i f the u n p a i r e d 3d electrons f r o m t h e C u

are are

2 +

d e l o c a l i z e d a n d o c c u p y a σ* c o n d u c t i o n b a n d f o r m e d as a r e s u l t of v a l e n t m i x i n g b e t w e e n the Cu(t ) 2g

Blasse r e p o r t e d

that magnetic

a n d s u l f u r (ρ ) π

2

susceptibility showed

Curie-Weiss

h a v i o r b e t w e e n 4 5 0 ° - 8 0 0 ° K . T h e effective m o m e n t w a s 4.3μ

Β

o n l y m o m e n t for C o w a s observed.

2 +

is 3 . 9 / ^ ) .

co-

orbitals. F o r C o R h S , 4

be­

(the spin

A t 400°K, antiferromagnetic

ordering

T h e o t h e r t h i o s p i n e l s w e r e a p p a r e n t l y too difficult to p r e ­

p a r e as single-phase m a t e r i a l s . P l o v n i c k a n d W o l d

—^—O^— *

Figure 8.

Cr S s

Â

reported

(16)

^ »*2

Ο

A"

Ο

Β*

•

vacancy

3

structure

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

the

26

PLATINUM GROUP METALS AND COMPOUNDS

preparation of the compounds MRI12X4 (M = Cr, Co, Ni; X = Se, Te) and Rh Te , which have the Cr S -type structure (space group 12/m), except for CoRh Te and NiRh Te , which are trigonal (space group Ρ 3 m 1). The monoclinic structure shown in Figure 8 is intermediate between the NiAs and Cdl types. The transition metal cations, A and B, occupy three-fourths of the octahedral sites between the layers of hexago­ nal close-packed anions. The packing sequence is such that B layers alternate with layers containing the A cations and vacancies. Ideally, the A cations are ordered with respect to the vacancies. When the vacancies are randomly arranged in A layers, trigonal symmetry results. The crystal class to which a given AB X compound belongs is indicative of the vacancy arrangement in that compound. The properties of a number of ternary rhodium chalcogenides are given in Table II. CoRh Se and NiRh Se are monoclinic, while CoRh Te and NiRh Te are trigonal. Co Se and Ni Te are also trigonal. The monoclinic structures observed for CrRh Se and CrRh Te are con­ sistent with reports (5, 6) that both Cr Se and Cr Te are monoclinic. In chalcogenides of this type, both the size and cZ-electron configuration of the cations, as well as the size and polarizability of the anion, are important in determining the relative stability of the ordered vs. random vacancy structure for a given composition. Rh Te also has the monoclinic Cr S -type structure (15). Geller (8) determined the crystal structure of RhTe and RhTe but did not investi­ gate intermediate compositions. Plovnick and Wold (16) have shown that in the rhodium-tellurium system at the composition Rh Te , order­ ing of the vacancies occurs with a consequent lowering of the symmetry to monoclinic. The Goodenough model (10) can account for the electrical proper­ ties of ternary rhodium chalcogenides of the type ARh X . The octahedrally coordinated Rh (4cZ ) has the low-spin configuration, and no contribution to the conductivity is made either by direct interaction of the cation t orbitals or by indirect e^-anion s,p interaction. This is not the case, however, for the M cations in the MRh X compounds. For example, Ni (t e ) may contribute to metallic conductivity via forma­ tion of partially-filled σ* bands as a result of nickel e^-anion s,p inter­ actions. Similar considerations apply to the other ternary rhodium chalcogenides. 3

4

3

2

4

2

4

4

2

3+

2+

2+

2+

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

2

2

2

4

2

4

4

2

4

3

4

4

3

2

3

3

4

3

4

4

2

4

3

4

4

4

2

3

2

3+

2g

4

4

6

a

2

2+

6

2g

4

2

g

v

Literature Cited (1) Bither, Τ. Α., private communication. (2) Blasse, G., Phys. Letters 1965, 19 No. 2, 110. (3) Blasse, G., Schipper, D. J., Phys. Letters 1963, 5 No. 5, 300.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch002

2.

WOLD

Phtinum Metal Chalcogenides

27

(4) Callaghan, Α., Moeller, C. W., Ward, R., Inorg. Chem. 1966, 5 No. 9, 1572. (5) Chevreton, M., Berodias, G., Compt. Rend. 1965, 261, 1251. (6) Chevreton, M., Bertaut, F., Compt. Rend. 1961, 253, 145. (7) Evans, R.C.,"Crystal Chemistry," 2nd ed., p. 151, Cambridge University Press, London, 1964. (8) Geller, S.,J.Am. Chem. Soc. 1955, 77, 2641. (9) Geller, S., Cetlin, Β.B.,Acta Cryst. 1955, 8, 272. (10) Goodenough, J. B., Proc. Colloq. Intern. Orsay 1965; C.N.R.S.1967,157 263. (11) Hulliger, F.,J.Phys. Chem. Solids 1965, 26, 639. (12) Hulliger, F., Nature 1964, 204, 644. (13) Hulliger, F., "Structure and Bonding," Vol. 4, Springer-Verlag, New York, 1968. (14) Jellinek, F. K., Acta Cryst. 1957, 10, 620. (15) Marcus, S. M., Butler, S. R., Phys. Rev. Letters 1968, 26A, 518. (16) Plovnick, R. H., Wold, Α., Inorg. Chem. 1968, 7, 2596. (17) Raub, C. J., Compton, V. B., Geballe, T. H., Matthias, B. T., Maita, J. P., Hull, G. W., J. Phys. Chem. Solids 1965, 26, 2051. (18) Rogers, D. B., Butler, S. R., Shannon, R. D., Inorg. Syn. 13, to be pub­ lished. (19) Rogers, D. B., Shannon, R. D., Sleight, A. W., Gillson, J. L., Inorg. Chem. 1969, 8, 841. (20) Wyckoff, R. W. G., "Crystal Structures," Vol. 1, 2nd ed., Wiley, New York, 1963. RECEIVED December 16, 1969. This work has been supported by ARPA and the U. S. Army Research Office, Durham, N. C.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3

Synthesis and Crystal Chemistry of Some

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

N e w Complex Palladium Oxides OLAF MULLER and RUSTUM ROY Materials Research Laboratory, The Pennsylvania State University, University Park, Pa. 16802

The synthesis and crystal chemistry of six new complex pa ladium oxides are described. The blackPbPdO has been tentatively indexed on a hexagonal basis witha = 10.902A andc = 4.654A. Sr PdO is body-centered orthorhombic witha = 3.970A,b = 3.544A, and c = 12.84A; the structure proposed for this compound is closely related to the KNiF structure. Three new black compounds of the MePdO type have been synthesized. All three have the cubic NaPtO structure with unit cell constants a = 5.826A for SrPdO, a = 5.747A for CaPdO, anda = 5.742A for CdPd O . In the system Mg-Pd-O, a spinel phase is formed(a = 8.501A) whose stoichiometry is believed to be MgPdO. 2

0

0

2

0

2

3

0

0

4

3

4

x

3

4

0

3

4

0

3

3

4

0

4

0

2

4

Tn our recent work on the systems Rh-O, Pt-O (5,7), and Au-O (5,6) -*· at high oxygen pressures, we prepared new compounds in all three systems. We conducted a similar study in the system Pd-O, but were not able to synthesize any new binary oxides of palladium. The divalent oxide, PdO, appears to be stable even at high oxygen pressures. Our work on the platinum oxides was recently extended to some ternary systems, and we have already reported on the inverse spinels Mg Pt0 , Zn Pt0 (10), on Cd Pt0 with the Sr Pb0 structure (9), on the tetragonal Cui_ Pt O, and the orthorhombic CuPt 0 (8). Compounds of the type MePt O with Me = Cd, Zn, Mg, Ni were synthesized at 800°-900°C and oxygen pressures near 200 arm. These phases are described in greater detail by Hoekstra, Siegel, and Gallagher (2). We encountered some difficulty in preparing these compounds in a pure state. Apparently, the maximum temperatures attainable with our equip2

4

2

4

2

x

4

x

2

4

3

3

6

e

28 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3.

M U L L E R

A N D

R O Y

New

Palladium

29

Oxides

m e n t ( . — 9 0 0 ° C ) are s t i l l too l o w for these reactions.

W e felt t h a t i t

m i g h t b e i n t e r e s t i n g to c o n d u c t a s i m i l a r s t u d y of some M e O - p a l l a d i u m o x i d e systems.

T h e present w o r k is c o n c e r n e d w i t h o u r s t u d y of

systems M e - P d - O , w h e r e M e =

the

P b , Sr, C a , C d , a n d M g .

R e l a t i v e l y l i t t l e is k n o w n a b o u t a n h y d r o u s oxides of p a l l a d i u m . T h e o n l y w e l l - c h a r a c t e r i z e d s i m p l e o x i d e is P d O , w h i c h has the P t S structure w i t h f o u r c o p l a n a r P d - O distances of 2.01 A (4,21).

Recently, G u i o t ( J )

p r e s e n t e d x - r a y e v i d e n c e s u g g e s t i n g t h a t a n e w p a l l a d i u m o x i d e surface c o m p o u n d is f o r m e d as a n i n t e r m e d i a t e step w h e n p a l l a d i u m m e t a l is o x i d i z e d i n a i r to P d O . H o w e v e r , the s t o i c h i o m e t r y of this c o m p o u n d is u n k n o w n , since i t c a n be o b t a i n e d o n l y as a m i n o r constituent, w i t h m a j o r amounts of P d m e t a l a n d P d O . H i g h e r a n h y d r o u s oxides

(e.g.,

Pd0 )

firmly

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

2

h a v e b e e n r e p o r t e d , b u t t h e i r existence has n e v e r b e e n

established. R e l a t i v e l y f e w t e r n a r y p a l l a d i u m oxides h a v e b e e n r e p o r t e d i n the literature. V a r i o u s a l k a l i m e t a l - p a l l a d i u m oxides are k n o w n Intermediate compounds tems w i t h L n =

2

L a , N d , Sm, E u , G d , and D y (3).

p y r o c h l o r e s of the t y p e L n P d 0 2

delafossite-like c o m p o u n d s studied

(14,15,16).

h a v e b e e n f o u n d i n s e v e r a l L n 0 - P d O sys-

2

7

A t h i g h pressures,

c a n b e p r e p a r e d (19).

Recently, the

P d C o 0 , P d C r 0 , and P d R h 0 2

3

2

2

have

been

(18).

Experimental Techniques C o l d - s e a l stellite b o m b s a n d h i g h o x y g e n pressures w e r e u s e d as d e s c r i b e d p r e v i o u s l y (6, 7, 8, 9, 10). A n o r d i n a r y p o t f u r n a c e was u s e d for heat treatments c a r r i e d out i n air. A s s t a r t i n g m a t e r i a l s , p u r i f i e d p a l l a d i u m b l a c k ( F i s h e r Scientific C o . ) was m i x e d i n t i m a t e l y w i t h the other oxides o r h y d r o x i d e s [ P b O , S r ( O H ) · 8 H 0 , C a O , C d O , M g ( O H ) ] . T h e m i x t u r e s g e n e r a l l y w e r e i n s e r t e d i n t o g o l d foils a n d heat t r e a t e d u n d e r v a r i o u s c o n d i t i o n s of t e m p e r a t u r e a n d o x y g e n p r e s sure. T h e runs w e r e q u e n c h e d a n d the p r o d u c t s e x a m i n e d b y x - r a y diffraction. T h e x - r a y d i f f r a c t i o n patterns w e r e m a d e w i t h a P i c k e r diffractometer, u s i n g N i - f i l t e r e d C u K r a d i a t i o n a n d glass-slide m o u n t s . T o d e r i v e accurate u n i t c e l l constants, s l o w - s c a n x - r a y patterns w e r e i n t e r n a l l y s t a n d a r d i z e d w i t h N a C l , K C 1 , or S i . T h e i n t e g r a t e d intensities w e r e o b t a i n e d b y m e a s u r i n g the area u n d e r e a c h p e a k w i t h a p l a n i m e t e r . T h e c a t i o n analyses w e r e p e r f o r m e d b y c o n v e n t i o n a l w e t - c h e m i c a l t e c h n i q u e s . T h e o x y g e n content was d e t e r m i n e d b y a r e d u c t i o n m e t h o d a n d b y n e u t r o n a c t i v a t i o n analysis. 2

2

2

Results PbPd0 . 2

The black P b P d 0

2

is p r e p a r e d c o n v e n i e n t l y b y h e a t i n g a

1:1 P b O - P d b l a c k m i x t u r e i n a i r at a b o u t 6 0 0 ° - 7 0 0 ° C for s e v e r a l days.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

P L A T I N U M

Table I.

M E T A L S

A N D

C O M P O U N D S

X - R a y Diffraction Powder D a t a for PbPdQj Hexagonal: a = 0

10.902A, c

0

— 4.654A

d obs. A

d cale, A

I obs.

hkl

4.72 3.544 2.833 2.727 2.607 2.360 2.327 2.282 2.087 1.964 1.784 1.769 1.693 1.657 1.593 1.573 1.531 1.492 1.438

4.72 3.539 2.832 2.726 2.607 2.360 2.327 2.282 2.087 1.964 1.784 1.770 1.693 1.657 1.593 1.574 1.531 1.492 1.438

2.0 5.1 100.0 19.7 2.8 17.0 12.0 1.7 4.1 4.0 18.4 20.3 1.5 15.1 22.8 1.8 1.3 0.4 16.6

200 111 211 220 301 400 002 311 202 321 420 222 331 402 511 600 103 113 521

1.392 1.375 1.363 1.334

1.391 1.375 1.363 1.335 (1.309 1.308 [1.304 1.261 1.239 1.2077 1.1987 (1.1802 U.1798 [1.1759 1.1635 1.1525 1.1446 1.1297 1.1196 1.0973

0.6 1.4 4.5 0.7

303 611 440 313 (620 441 [602 323 413 711 503 (800 333 [442 004 631 513 204 721 433

y

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

GROUP

1.305B 1.261 1.239 1.2075 1.1984 1.1779 1.1634 1.1523 1.1444 1.1296 1.1195 1.0972

1.0701 1.0527 1.0435 1.0358

{!S

1.0701 1.0526 1.0436 1.0356

1.0 0.6 1.2 0.2 0.6 12.4 2.8 8.0 9.5 1.4 0.4 0.7 9 8

3.7 10.7 3.1 6.8

{£

224 802 404 731

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3.

M U L L E R

New

A N D R O Y

FaUadium

31

Oxides

A n analysis f o r o x y g e n b y n e u t r o n a c t i v a t i o n y i e l d e d 9 . 2 % lated: 9.26% Ο b y w e i g h t ) . P b P d 0

Ο

(calcu­

is a p p a r e n t l y u n s t a b l e at t e m p e r a ­

2

tures a b o v e *—820 ° C , w h e r e a m i x t u r e of P b O a n d P b P d

is o b t a i n e d i n

3

p l a c e of P b P d 0 . 2

T h e x - r a y p o w d e r p a t t e r n of P b P d 0

2

( T a b l e I ) has b e e n t e n t a t i v e l y

i n d e x e d o n the basis of a h e x a g o n a l u n i t c e l l w i t h a = 0

4.654A.

T h i s m a y represent o n l y a p s e u d o c e l l .

10.902A a n d c

=

Q

N o single crystal data

are a v a i l a b l e , since the p r o d u c t c o u l d o n l y b e o b t a i n e d as a fine p o w d e r . T a b l e I i n d i c a t e s t h a t s e v e r a l extinctions o c c u r w h i c h are n o t c h a r a c t e r ­ i s t i c f o r a n y h e x a g o n a l space g r o u p ; e.g., f o r KkO, h = Sr PdC>3. 2

2n and k =

2n.

A y e l l o w - b r o w n c o m p o u n d , S r P d 0 , is f o r m e d w h e n t h e 2

3

a p p r o p r i a t e s t a r t i n g m i x t u r e ( i n p e l l e t f o r m ) is fired at 9 5 0 ° C i n a i r for

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

s e v e r a l days. T h e c o m p o u n d is t h e r m a l l y q u i t e stable, e v e n at 1 2 0 0 ° C . It dissolves r a p i d l y i n d i l u t e a c i d s , a n d w h e n b r o u g h t i n contact w a t e r , i t alters to a n u n i d e n t i f i e d h y d r a t e d p r o d u c t . the f o r m u l a .—Sri. Pdi. o0 . 93

0

w i t h χ as h i g h as 0.6.

3+a

an i d e a l f o r m u l a of S r P d 0 2

with

A n a l y s e s l e a d to W e have assumed

for reasons d i s c u s s e d b e l o w .

3

R o t a t i o n a n d W e i s s e n b e r g patterns w e r e t a k e n of a s i n g l e c r y s t a l of S r P d 0 . T h e s i n g l e - c r y s t a l d a t a l e a d to a b o d y - c e n t e r e d o r t h o r h o m b i c 2

3

u n i t c e l l . P o w d e r d a t a (a

=

Q

3.970A, b

=

Q

3.544A, c

0

=

1 2 . 8 4 A ) are i n

g o o d a g r e e m e n t w i t h the s i n g l e - c r y s t a l d a t a . T h e o n l y e x t i n c t i o n s f o u n d w e r e those f o r b o d y - c e n t e r i n g ; t h u s , the f o u r p o s s i b l e space g r o u p s a r e D

2 h

2 5

- J m m m , ό2*-Ι222,

ώ2 -Ι2 2 2 , 9

1

1

and c

1

2 v

2 0

-Irara2.

B o t h s y m m e t r y a n d u n i t c e l l constants are s i m i l a r to t h e c o r r e s p o n d ­ i n g v a l u e s of K N i F 2

4

t y p e c o m p o u n d s , as is s h o w n i n T a b l e I I .

w e h a v e f o u n d t h a t a reasonable s t r u c t u r e c a n b e d e r i v e d for w h i c h is closely r e l a t e d to the K N i F 2

t u r e , t h e space g r o u p D

2 h

2 5

Indeed, Sr Pd0 2

3

s t r u c t u r e . I n this p r o p o s e d s t r u c ­

4

- Z r a r a r a is a s s u m e d a n d t h e atoms are p l a c e d

as f o l l o w s : 4 S r i n (4i) : OOz, OOF + 2 P d i n (2a) : 000 + 2 Ο i n (26)-: O H +

b.c. w i t h ζ =

0.355

b.c. w i t h ζ =

0.16

b.c. b.c.

4 Ο i n (4i) : 00z, OOz +

W i t h this a s s u m p t i o n , intensities for the p o w d e r p a t t e r n w e r e c a l ­ c u l a t e d i n t h e same m a n n e r as d e s c r i b e d p r e v i o u s l y (8).

A l l tempera­

t u r e coefficients w e r e a s s u m e d to b e zero. T h e c a l c u l a t e d intensities are l i s t e d i n T a b l e I I I a n d c o m p a r e q u i t e f a v o r a b l y w i t h the o b s e r v e d i n ­ tensities. T h e i n t e n s i t y d i s c r e p a n c y f a c t o r R = w a s c a l c u l a t e d as 6.6.

100 ( 2 | I

0

—

I | c

h)

I n c a l c u l a t i n g the R - f a c t o r , t h e intensities w h i c h

w e r e too w e a k to b e o b s e r v e d w e r e a s s i g n e d J obs. v a l u e s of zero.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

The

32

P L A T I N U M

Table II.

G R O U P

M E T A L S

Compound

a , A

Sr Ir0 Sr Rh0 Sr Ru0

4

2

4

3.89 3.85 3.870

3

3.970

2

b , A

0

2

4

Sr Pd0

Table III.

0

3.544

Co, A

Ref.

12.92 12.90 12.74

(12) (13) (13)

12.84

present work

Symmetry Space Group Structure Type Tetragonal K NiF 2

4

Orthorhombic

2

0

Space group:

=

Q

D

2 2

h

5

—

Immm;

3.544A, a n d c

Q

=

12.84A

n.o. = n o t o b s e r v e d .

d obs., A

d cale, A

I obs.

I calc.

hkl

6.44 n.o. 3.419 3.217 2.912 2.730 2.643 2.447

6.42 3.793 3.416 3.210 2.911 2.730 2.644 2.445

10.2 n.o. 3.2 2.6 64.0 73.9 100.0 1.8

22.4 0.1 3.3 2.4 67.6 76.2 98.9 2.2 J 10.2 \22.2 14.0 6.4 25.2 1.9 17.2 / 0.6

002 101 011 004 103 013 110 112 105 006 015 114 200 202 020 211 022 204 107 116 017 213 008 024 123 206 215 118 125 026 109 019 220

2.141

g;}»

33.3

2.079 2.041 1.985 1.896 1.772 1 711 '

2.079 2.041 1.985 1.896 1.772 fl-716 \1.708 1.688 1.665 [1.663 1.629

12.8 6.4 25.8 1.5 18.9

1

/

1.663 n.o.

1.605

n.o. 1.513 1.455 1.436 1.368 1.342 1.322

structure

X - R a y Diffraction Powder D a t a for S r P d 0

O r t h o r h o m b i c : a — 3.970A, b Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

C O M P O U N D S

Structural D a t a for Some Strontium-Noble Metal Oxides Unit Cell Constants

2

A N D

1

7

1A

35.2 n.o.

{;5jg 36.8 :

1.551 1.514 1.455 1.436 (1.372 1.369 [1.365 1.343

{}fg

1 0.6

n.o. 20.4 14.3 6.2

21.8 2.9 14.7

0.9 [30.3 0.2 /30.0

1 0.4 5.1 19.7 11.8 7.8 f 9.2 4.6 [ 9.3 2.2 / 3.0 112.2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3

3.

M U L L E R

A N D

New

R O Y

Palladium

Table III.

33

Oxides

(Continued)

O r t h o r h o m b i c : a = 3.970A, b — 3.544A, a n d c = 0

Q

Space g r o u p :

2 2

5

h

—

Immm;

n.o.

12.84A

not observed.

d cale, A

I obs.

I calc.

hkl

1.295 1.284

n.o. n.o.

1.264

j}|<*

6.7

1.241

(Jig

n.o. n.o. n.o. 1.189

1.222 1.217 1.213 1.190

n.o. n.o. n.o. 3.0

1.176

|J;gJ

1.0

1.155

|; J»

1.1 0.2 5.4 0.2 4.3 8.3 0.4 0.4 0.6 3.8 0.1 1.5 0.7

2.3

222 0-0-10 303 217 208 310 224 312 127 028 031 305 314 1110 033 130 226 1-0-11 132 0-1-11 219

d obs. A y

n.o. n.o.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

D

0

:

1.136 1.124 1.108 1.101

/ 1 J \

1 L 5

/ 1 /

1 / 4.9 ΙΛ

\ 6.4 10.0 4.3

10.1 1.125 1.120 [1.115 1.109 1.101

17.7

14.90.3

4.6 4.2

3.5

002 reflection w a s e x c l u d e d , since this l o w - a n g l e reflection d i d n o t r e ­ ceive t h e f u l l i n t e n s i t y of t h e x - r a y b e a m . W i t h t h e a s s u m e d a t o m i c coordinates, d i v a l e n t p a l l a d i u m is s u r ­ r o u n d e d b y f o u r c o p l a n a r ( r e c t a n g u l a r ) oxygens, t w o at 1.985A a n d t w o at 2.054A. T h e s t r o n t i u m atoms a r e s u r r o u n d e d b y seven nearest o x y g e n n e i g h b o r s , f o u r at 2.67A, t w o at 2.57A, a n d o n e at 2.50A. T h i s leads to a n average S r - O s e p a r a t i o n of 2.62A, w h i c h is i n v e r y g o o d agreement w i t h the s u m o f t h e i o n i c r a d i i , 2.61A ( 1 7 ) . T h e a b o v e distances are b a s e d o n the t w o a p p r o x i m a t e ζ parameters (ζ = 0.355 f o r S r a n d ζ = 0.16 f o r Ο i n 4 i ) w h i c h are b e l i e v e d to b e a c c u r a t e w i t h i n =b0.01A. T h e s e t w o v a r i a b l e z-parameters w e r e chosen o n t h e basis o f a f e w t r i a l c a l c u l a t i o n s . W e h a v e n o t b o t h e r e d to d o a refinement w i t h t h e p o w d e r d a t a . A n y f u t u r e refinement is best

carried out w i t h

s i n g l e - c r y s t a l d a t a , since

single

crystals are easily o b t a i n a b l e . T h e structure c a n - b e c o n s i d e r e d as a n o r t h o r h o m b i c a l l y d i s t o r t e d K NiF 2

4

t y p e , f r o m w h i c h £ o f t h e oxygens h a v e b e e n r e m o v e d i n a n

o r d e r e d w a y . I f these m i s s i n g oxygens are i n s e r t e d — 2 Ο i n (2d), £0% + b.c. i n space g r o u p Immm—the

stoichiometry S r P d 0 2

4

is o b t a i n e d . A s

has a l r e a d y b e e n i n d i c a t e d , o u r attempts to d e t e r m i n e t h e o x y g e n c o n -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

34

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

tent i n S r P d 0 h a v e f a i l e d to y i e l d a v a l u e consistent w i t h the a s s u m e d 2

formula.

3

Somewhat

higher oxygen

contents

are o b t a i n e d , u p to

S r P d 0 . 6 s t o i c h i o m e t r y . A f t e r c o n s i d e r i n g the p o s s i b i l i t y t h a t the 2

3

the (2d)

positions i n the s t r u c t u r e are o c c u p i e d b y significant amounts of o x y g e n , w e rejected this h y p o t h e s i s f o r t w o reasons: (f) W i t h i n c r e a s i n g a m o u n t s of o x y g e n i n (2d), the i n t e n s i t y agreem e n t b e c o m e s s i g n i f i c a n t l y p o o r e r , e.g., the 101 reflection b e c o m e s c o m p a r a b l e i n i n t e n s i t y to the O i l a n d the 103 reflection becomes m o r e intense t h a n the 013, i n c o n t r a d i c t i o n to o u r observations. (it) A b n o r m a l l y short P d - O distances ( 1 . 7 7 2 A ) w o u l d b e at least 0.2A shorter t h a n the e x p e c t e d b o n d l e n g t h .

formed,

W e b e l i e v e that the h i g h o x y g e n content m a y p o s s i b l y b e c a u s e d b y s o r p t i o n of H 0 or C 0 Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

2

a n d absorbs C 0

p r i o r to analysis since S r O is h i g h l y h y g r o s c o p i c

2

f r o m the air.

2

Addendum. W h i l e this a r t i c l e w a s b e i n g refereed, a p a p e r a p p e a r e d d e s c r i b i n g the c r y s t a l s t r u c t u r e of S r C u 0 2

Sr Pd0 2

and S r C u 0

3

2

3

It is a p p a r e n t that

(20).

are i s o t y p i c , a l t h o u g h the G e r m a n authors

3

h a v e chosen for S r C u 0 2

3

(20)

a different o r i g i n w i t h the a,b, a n d c-axes i n t e r -

c h a n g e d , c o m p a r e d w i t h those selected for S r P d 0 . T h i s difference i n 2

3

c h o i c e c a n b e a t t r i b u t e d to the fact that w e h a v e d e r i v e d the structure of S r P d 0 f r o m the K N i F 2

3

2

t y p e a n d therefore h a v e chosen s i m i l a r set-

4

tings. T h e structure of S r C u 0 2

3

was d e r i v e d f r o m P a t t e r s o n a n d F o u r i e r

syntheses w i t h o u t d r a w i n g a n y a n a l o g y to the K N i F 2

S r P d 0 , C a P d 0 , and C d P d 0 . 3

4

3

4

3

4

4

structure.

T h e three n e w phases, S r P d 0 , 3

4

C a P d 0 , a n d C d P d 0 , c a n b e p r e p a r e d easily b y h e a t i n g the reagent 3

4

3

4

g r a d e m i x t u r e s at 9 0 0 ° C a n d 200 a r m of oxygen.

H o w e v e r , h i g h oxygen

pressures are not r e q u i r e d , a n d a l l t h r e e phases c a n b e m a d e b y h e a t i n g the s t a r t i n g m i x t u r e s i n a i r . I f the synthesis is c a r r i e d out i n a i r , the p r o d u c t s are g e n e r a l l y not p u r e a n d c o n t a i n significant amounts of e n d component

oxides

and/or

palladium metal.

To

help eliminate

these

i m p u r i t i e s , the f o l l o w i n g p o i n t s s h o u l d b e n o t e d : (i) T h e s t a r t i n g m i x t u r e s h o u l d c o n t a i n some excess M e O o x i d e or h y d r o x i d e a b o v e the s t o i c h i o m e t r i c 1:3 r a t i o . T h i s results i n the f o r m a t i o n of some excess S r P d 0 , C a O , or C d O . A l l three of these i m p u r i t i e s c a n b e d i s s o l v e d a w a y w i t h d i l u t e n i t r i c a c i d , l e a v i n g the i n s o l u b l e M e P d 0 behind. 2

3

3

4

(it) P a l l a d i u m m e t a l i m p u r i t i e s c a n b e r e m o v e d w i t h a q u a r e g i a . H o w e v e r , S r P d 0 , C a P d 0 , a n d C d P d 0 w i l l dissolve s l o w l y i n a q u a r e g i a , at least to some extent. T h u s , a n y t r e a t m e n t w i t h a q u a r e g i a s h o u l d not b e p r o l o n g e d . (Hi) R e g r i n d i n g , r e m i x i n g , a n d r e h e a t i n g the c o m p r e s s e d pellets m a y h e l p r e d u c e the i m p u r i t i e s . (iv) T h e synthesis of C d P d 0 i n air is best c a r r i e d out at 8 0 0 ° 8 2 0 ° C , w h i l e f o r S r P d Q a n d C a P d 0 ~ 9 5 0 ° C is r e c o m m e n d e d . L o w e r 3

4

3

4

3

3

3

4

4

4

3

4

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3.

M U L L E R

New Palladium

A N D R O Y

Table I V .

35

Oxides

X - R a y Diffraction Powder D a t a for S r P d 0 3

Primitive Cubic: a =

5.826A. S . G . : o -Pm3n

( N a P t 0 structure)

3

0

4

h

x

3

4

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

(n.o. = n o t o b s e r v e d ) d obs., A

d cale, A

I obs.

I calc.

hkl

4.13 2.913 2.606 2.379 2.060 1.842 1.682 1.616 1.557 1.456

4.12 2.913 2.605 2.378 2.060 1.842 1.682 1.616 1.557 1.456

1.4 12.0 100.0 61.6 1.0 0.4 17.2 27.1 36.4 21.9

1.7 12.2 105.6 65.8 1.0 0.4 17.1 24.1 34.0 19.2

110 200 210 211 220 310 222 320 321 400

1" 374 ' A

d

4

1.303 1.271 1.242 n.o.

1142 l

e

l

4

1

1.0637 1.0302 °n Q71 η ' 0.9576

n ,

y

/

i

1

O S '

373

U

n.o. n.o. 0.8782 n « A « *

°0.8589 0.8409 8 6 8 5

/

Ό ό

5.6 22.9 8.3 n.o.

OS

ί11.143 ·

J

ι n«90

u

I"

11.373 1.303 1.271 1.242 1.189 143

°'

/1.0819 \1.0819 1.0637 1.0299 /0.9991 \0.9991 J 0.9710 \0.9710 0.9578

2

L

1

10.8 13.7 ·°·

η

Q

Q

* 6.2

d

{SS

y

"·

8

0.9212 0.8990 0.8783 /0.8685 \0.8685 0.8590 0.8409

n.o. n.o. 11.1 1

Q

0

4 3 1

2

\ 0.1 J 7.0 \13.8 10.5 13.7 / 0.1 \ 0.1 / 0.7 \ 2.9 5.9

510 520 432 521 440 530 433 600 442 610

{îî

%ι

0.0 0.2 11.1 / 6.8 \13.4 10.9 10.9

Q

· 10.1 10.2

1 9

3 3 0

411 420 421 332 422

I '

ό

,

9 1

0 Λ

1 0.2 5.2 21.4 7.9 0.1

9

620 541 622 630 542 631 444

t e m p e r a t u r e s g i v e l o w e r c o n v e r s i o n rates, w h i l e significantly h i g h e r t e m ­ peratures result i n t h e d e c o m p o s i t i o n of the p r o d u c t s . T y p i c a l analyses of t h e p r o d u c t s y i e l d e d t h e f o l l o w i n g

formulas:

Sri.oiPd .oo0 .22, Cao.99Pd .oo0 .o5> a n d C d o . 5 P d . o o 0 . . T h e s t r o n t i u m 3

4

3

4

9

3

4

03

c o m p o u n d gives h i g h e r t h a n e x p e c t e d o x y g e n contents, e s p e c i a l l y w h e n the samples are p r e p a r e d at h i g h o x y g e n pressures.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

36

P L A T I N U M

T h e x - r a y p o w d e r d a t a for S r P d 0 3

4

GROUP

M E T A L S

A N D

C O M P O U N D S

are g i v e n i n T a b l e I V . C a P d 0 3

4

a n d C d P d 0 g i v e v e r y s i m i l a r p o w d e r patterns. A l l three patterns c a n b e 3

4

i n d e x e d o n t h e basis of a p r i m i t i v e c u b i c u n i t c e l l w i t h c e l l constants of 5.826, 5.747, a n d 5.742A for S r P d 0 , C a P d 0 , a n d C d P d 0 , respec­ 3

4

3

4

3

4

t i v e l y . I n t e n s i t y c a l c u l a t i o n s w e r e c a r r i e d out i n a s i m i l a r m a n n e r as for S r P d 0 , a s s u m i n g the N a P t 0 2

3

x

3

4

structure (22,

p l a c e d as f o l l o w s i n space g r o u p

T h e atoms

23).

were

o -Pm3n: 3

h

2 S r ( C a or C d ) i n (2a) : (ΟΟΟ,ΗΙ) 6 P d i n (6c) : ±

(10*, O )

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

8 Ο i n (8e) : ± (ΙΗ,ΗΪΟ) Table V .

Structural D a t a for Compounds with the N a P t 0 x

Cubic, S.G.: o

h

Interatomic

3

-

3

4

Structure

Pm3n

Distances,

A

a

Composition

a, A

Pt-0 or Pd-O, square planar

Pt 0 Mg Pt 0 Na Pt 0

5.585 5.621 5.69

1.974 1.987 2.01

2.418 2.434 2.46

2.792 2.810 2.84

(7) (ID (22,23)

5.64 5.742 5.747 5.826

1.99 2.030 2.032 2.059

2.44 2.486 2.488 2.523

2.82 2.871 2.873 2.913

(16) Present work Present work Present work

3

4

x

3

x

3

Na Pd 0 CdPd 0 CaPd 0 SrPd 0 x

3

3

4

4

4

3

3

4

4

4

0

Me-O, 8-fold, cubic

Shortest, Pt-Pt or Pd-Pd

Reference

The interatomic distances for C d P d s O * , CaPd C>4, and S r P d 0 4 are believed to be accurate to within db 0.002A. This small error is a function only of the accuracy of the do cell edge measurements, since there are no variable positional parameters in the a

3

3

N a x P t 0 * structure. 3

T a b l e I V shows t h a t the i n t e n s i t y a g r e e m e n t is q u i t e g o o d . i n t e n s i t y d i s c r e p a n c y factors R =

100 (%\I

The

— 7 |)/2(J ) were calcu­

Q

C

0

l a t e d as 5.8, 7.8, a n d 8.4 for S r P d 0 , C a P d 0 , a n d C d P d 0 , respec­ 3

tively.

4

3

4

3

4

I n T a b l e V , the i n t e r a t o m i c distances for these c o m p o u n d s

c o m p a r e d w i t h the distances f o u n d for other N a P t 0 - t y p e phases. x

s q u a r e p l a n a r P d - O b o n d lengths a n d t h e c u b i c Sr-O,

3

4

are The

(eight-coordinated)

C a - O , a n d C d - O distances are i n g o o d agreement w i t h the ex­

p e c t e d values. S q u a r e p l a n a r c o o r d i n a t i o n is c o m m o n for d i v a l e n t p a l l a ­ d i u m c o m p o u n d s , a n d the e i g h t - f o l d ( c u b i c ) e n v i r o n m e n t for S r , C a , 2 +

and C d

2 +

2 +

is e x p e c t e d f o r these ions. T h e r e l a t i v e l y short P d - P d distances

m a y i n d i c a t e the presence of some i n t e r - m e t a l l i c b o n d i n g . I n these c o m -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3. MULLER AND ROY

New Palladium Oxides

37

pounds, the palladium atoms are apparently completely ordered in the (6c) sites. We have found no x-ray evidence for any noticeable disorder between the two different cations in CaPd 0 . Because of the strong preference of Pd for square planar coordination, it can be assumed that no such disorder exists in SrPd 0 and CdPd 0 , although this could not be proved easily by x-ray methods since the atomic scattering factors for Sr, Cd, and Pd are very similar. Mg Pd0 . When Mg(OH) -Pd black mixtures are heated at high oxygen pressures—e.g., at 900 °C and 200 atm of oxygen—a poorly crystallized spinel phase is formed with a = 8.501A. We have not yet succeeded in preparing this spinel in a pure state, since this phase is always accompanied by some unreacted MgO and PdO. From crystal-chemical considerations and from the x-ray intensities, we have tentatively assigned the stoichiometry Mg Pd0 to this phase. Mg Pd0 is apparently an inverse spinel with Pd occupying octahedral sites. The unit cell constant for Mg Pd0 , a = 8.501A, is slightly smaller than the corresponding value for Mg Pt0 , a = 8.521 A (10), owing to the slightly smaller ionic radius for Pd (17). 3

4

2+

3

2

4

4

3

4

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

0

2 4+

2

4

4

2

4

0

2 4+

4

0

Acknowledgment We thank W. A. Jester for the neutron activation analyses. This work was supported by the Advanced Research Projects Agency, Contract No. DA-49-083 OSA-3140, and by the U. S. Army Electronics Command, Contract DA28-043 AMC-01304 (E). Literature Cited (1) Guiot, J. M., J. Appl. Phys. 1968, 39, 3509. (2) Hoekstra, Henry R., Siegel, Stanley, Gallagher, Francis X., ADVAN. CHEM. SER. 1970, 98, 39. (3) McDaniel, C. M., Schneider, S. J.,J.Res. Natl. Bur. Std. 1968, 72A, 27. (4) Moore, W. J., Pauling, L,J.Am. Chem. Soc. 1941, 63, 1392. (5) Muller, O., Roy, R., Am. Ceram. Soc.Bull.1967, 46, 881. (6) Muller, O., Roy, R.,J.Inorg.Nucl.Chem. 1969, 31, 2966. (7) Muller, O., Roy, R.,J.Less-Common Metals 1968, 16, 129. (8) Ibid., 1969, 19, 209. (9) Ibid., 1970, 20, 161. (10) Muller, O., Roy, R., Mater. Res. Bull. 1969, 4, 39. (11) Muller, O., Roy, R., unpublished data. (12) Randall, J. J., Katz, L., Ward, R.,J.Am. Chem. Soc. 1957, 79, 266. (13) Randall, J. J., Ward, R.,J.Am. Chem. Soc. 1959, 81, 2629. (14) Sabrowsky, H., Hoppe, R., Naturwissenschaften 1966, 53, 501. (15) Scheer, J. J., Dissertation, Leiden, Netherlands, 1956. (16) Scheer, J. J., van Arkel, A. E., Heyding, R. D., Can. J. Chem. 1955, 33, 683.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

38

PLATINUM GROUP METALS AND COMPOUNDS

Shannon, R. D., Prewitt, C. T., Acta Cryst. 1969, B25, 925. Shannon, R. D., Rogers, D. B., Prewitt, C. T., in press. Sleight, A. W., Mater. Res. Bull. 1968, 3, 699. Teske, C. L., Muller-Buschbaum, H., Z. Anorg. Allgem. Chem. 1969, 371, 325. Waser, J., Levy, Η. Α., Peterson, S. W., Acta Cryst. 1953, 6, 661. Waser, J., McClanahan, E. D.,J.Chem. Phys. 1951, 19, 199. Ibid., 1951, 19, 413. RECEIVED February 2, 1970.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch003

(17) (18) (19) (20) (21) (22) (23)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

4

Reaction of Platinum Dioxide with Some Metal Oxides

HENRY R. HOEKSTRA, STANLEY SIEGEL, and FRANCIS X. GALLAGHER

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

Argonne National Laboratory, Argonne, Ill. 60439 The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kilobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO -rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with PtO to form cubic Pb Pt O . Several corundum-type sesquioxides exhibit measurable solubility in PtO . Two series of compounds are formed with metal monoxides: M PtO (where M is Mg, Zn, Cd) and MPt O (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 2

2

2

2

7

2

2

4

3

6

'Tphe literature on anhydrous binary or ternary platinum oxides is relatively limited. Muller and Roy (6) have reviewed the simple platinum oxides and were able to confirm the existence of only two oxides, P t 0 and Pt0 , with the dioxide existing in two crystal modifications. Shannon (13) has discussed the preparation and properties of orthorhombic Pt0 . Ternary oxides of platinum include several with the alkali metals (NaJPtsO^ Na Pt0 , L i P t 0 ) (12) and with the alkaline earths [Ba Pt 0 (18), Sr Pt 0 , and Sr PtO (10)]. More recent work has been reported on T l P t 0 (4) and the rare earth-platinum pyrochlores (3, 17), as well as the spinels Z n P t 0 and M g P t 0 (5). The investigations of platinum pyrochlores have demonstrated the effectiveness of high pressure techniques in the synthesis of anhydrous oxides when one or both reactants have limited thermal stability. The bulk of the work reported here represents a continuation of an exploration of metal oxide-platinum oxide systems at high pressure. 3

4

2

2

2

3

2

7

3

3

2

7

2

2

7

2

3

4

2

e

4

2

4

39 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

40

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

Equipment and Procedure T h e h i g h pressure a p p a r a t u s u s e d i n this w o r k is a t e t r a h e d r a l a n v i l apparatus. D e t a i l s of the e q u i p m e n t , the o p e r a t i n g p r o c e d u r e , a n d the sample assembly have been described previously (2) r e p e a t e d here.

B r i e f l y , the p o w d e r e d

and w i l l not

be

o x i d e samples are w r a p p e d i n

p l a t i n u m or i n g o l d f o i l to isolate t h e m , as m u c h as possible, f r o m r e a c t i o n w i t h m a t e r i a l s other t h a n the reactant m i x t u r e . W e s h a l l see t h a t o n occasion the o x i d e samples w i l l react w i t h the p l a t i n u m f o i l c o n t a i n e r to g i v e l o w e r v a l e n c e p l a t i n u m oxides. A s a r u l e , three o x i d e samples, w h i c h h a v e b e e n w r a p p e d i n f o i l a n d pressed i n t o pellets, are l o a d e d i n t o the s a m p l e c a v i t y (•—1

cc v o l u m e ) of a p y r o p h y l l i t e t e t r a h e d r o n for e a c h

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

h i g h pressure r u n . I n a t y p i c a l e x p e r i m e n t , the t e t r a h e d r o n w i t h its three samples is c o m ­ pressed to 40 k b pressure; the s a m p l e c a v i t y is h e a t e d to 1200 ° C a n d m a i n t a i n e d at that t e m p e r a t u r e for a n h o u r b e f o r e b e i n g q u e n c h e d room temperature.

F i n a l l y , pressure is released s l o w l y .

to

A l t h o u g h the

b u l k of o u r experiments h a v e b e e n r u n at 40 k b pressure, the range i n pressure a p p l i e d has v a r i e d f r o m 20 to 60 k b ; e x p e r i m e n t a l temperatures v a r i e d f r o m 500° to 1600 ° C . W e find that u n d e r these e x p e r i m e n t a l c o n d i t i o n s loss of a n a p p r e ­ c i a b l e a m o u n t of o x y g e n f r o m the s a m p l e p e l l e t occurs v e r y r a r e l y , e v e n t h o u g h the oxides are h e a t e d to several h u n d r e d degrees a b o v e t h e i r d e c o m p o s i t i o n t e m p e r a t u r e at a t m o s p h e r i c pressure.

E x c e p t i o n s to this

r u l e o c c u r w i t h the f o r m a t i o n of a n y stable oxide phase w h i c h does not u t i l i z e a l l of the oxygen present i n the i n i t i a l reactant m i x t u r e . T h i s "excess" o x y g e n is lost r a t h e r r a p i d l y f r o m the s a m p l e enclosure. O u r i n v e s t i g a t i o n of the properties of the p l a t i n u m oxides i n c l u d e s x-ray, i n f r a r e d , a n d t h e r m a l analysis. P o w d e r x - r a y d a t a w e r e o b t a i n e d w i t h a P h i l i p s 114.59 m m c a m e r a , u s i n g either N i - f i l t e r e d C u r a d i a t i o n or V - f i l t e r e d C r r a d i a t i o n . C e l l parameters w e r e o b t a i n e d u s i n g a least squares refinement, a n d are b a s e d o n C u Κα = 2.2909. T h e dta-tga

1.5418 A a n d C r Κα —-

results w e r e o b t a i n e d o n a M e t t l e r r e c o r d i n g t h e r m o -

a n a l y z e r over the t e m p e r a t u r e i n t e r v a l 2 5 ° - 1 4 0 0 ° C , w i t h a h e a t i n g rate of 6 ° / m i n u t e a n d a s e n s i t i v i t y of 100 μΥ.

I n f r a r e d spectra to 200 c m "

w e r e t a k e n w i t h a B e c k m a n I R - 1 2 spectrophotometer.

1

N u j o l mulls were

s p r e a d o n p o l y e t h y l e n e disks for the l o w f r e q u e n c y p o r t i o n of the spec­ t r u m a n d o n K B r plates for the frequencies a b o v e 400 c m " .

Platinum

1

d i o x i d e w a s p r e p a r e d b y the r e a c t i o n of K P t C l 2

purity) with molten K N 0 s o l u t i o n of the K N 0 for several hours. than 0.2%

3

3

at 4 0 0 ° C .

4

or K P t C l 2

6

(99.9%

T h e dioxide was recovered

by

i n water and purified by heating i n aqua regia

S p e c t r o c h e m i c a l analysis of the p r o d u c t s h o w e d less

of a l k a l i metals, a n d no w a t e r or h y d r o x y l i o n w a s

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

detect-

4.

H O E K S T R A

E T

Reaction

A L .

Table I.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

41

Dioxide

X - r a y Powder Data for a - P t 0 a = 3.100(2)

Hexagonal

a

of Platinum

hkl

d

001 100 101 002 102 110 111 003 200 201 112 103 202 113 210 211 203 212 300 301 114 302

4.107 2.664 2.241 2.065 1.637 1.543 1.448 1.381 1.337 1.2734 1.2388 1.2287 1.1255 1.0309 1.0126 0.9841 0.9628 0.9111 0.8945 0.8752 0.8629 0.8218

c = 4.161(3)

2

A

I calcd

I obsd

a

100 100 170 15 100 50 70 10 25 50 40 50 50 40 40 90 45 115 30 60 80 75

60 100 90 10 60 90 70 1 45 50 30 15 35 5 55 55 20 60 35 40 20 100

Based on C d l - t y p e structure. 2

able b y i n f r a r e d analysis. M e t a l oxides u s e d i n the reactions w i t h P t 0

2

w e r e u s u a l l y reagent grade c h e m i c a l s ; exceptions i n c l u d e d oxides s u c h as F e O , C r 0 , M n O , M n 0 , V 0 , a n d M o 0 , w h i c h w e r e p r e p a r e d b y 2

accepted

2

procedures

3

2

2

f r o m reagent grade s t a r t i n g m a t e r i a l s . P u r i t y

of

these p r o d u c t s w a s c o n f i r m e d b y x-ray, t h e r m a l , a n d c h e m i c a l analysis.

Results «-Pt0 . 2

S e v e r a l proposals c o n c e r n i n g t h e structure of the a m b i e n t

pressure f o r m of P t 0

2

h a v e b e e n r e v i e w e d b y M u l l e r a n d R o y (6).

Diffi-

culties arise p r i n c i p a l l y f r o m the p o o r c r y s t a l l i n i t y w h i c h characterizes this phase, regardless of the h e a t i n g t i m e e m p l o y e d i n its p r e p a r a t i o n . D i s o r d e r is p a r t i c u l a r l y t r o u b l e s o m e i n the o d i r e e t i o n of the h e x a g o n a l structure since hkl lines w i t h 1 ^ 0

b e c o m e i n c r e a s i n g l y w e a k a n d diffuse

w i t h increase i n 1. O u r experience w i t h the synthesis of <*-Pt0

2

confirms p r e v i o u s r e -

ports o n the c h a r a c t e r i s t i c d i s o r d e r e d s t r u c t u r e of the oxide.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Vaughn

42

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

L e i g h , one of o u r student aides, n o t e d t h a t the t h i n film of P t 0 forms o n t h e surface of the m o l t e n K N 0

3

2

which

shows m u c h less d i s o r d e r a n d

gives a m u c h i m p r o v e d p o w d e r p a t t e r n over the b u l k d i o x i d e i n the n i t r a t e m e l t . T a b l e I gives the x - r a y p o w d e r d a t a o b t a i n e d f r o m s u c h a Pt0

2

surface layer. T h e c a l c u l a t e d h e x a g o n a l c e l l parameters are a

=

3.100(2) a n d c — 4 . 1 6 1 ( 3 ) A ; the x - r a y d e n s i t y is 10.90 g r a m s / c m . 3

W e p r e f e r the l a y e r e d C d l - t y p e s t r u c t u r e ( s p a c e g r o u p P 3 m l — 2

D

3 d

3

) for « - P t 0 . 2

E v e n t h o u g h the i n t e n s i t y agreement is o n l y f a i r i n

o u r " o r d e r e d " phase, i t is m u c h s u p e r i o r to that of the b u l k m a t e r i a l , a n d w o u l d b e e x p e c t e d to s h o w f u r t h e r i m p r o v e m e n t as o r d e r i n g is i n c r e a s e d i n the c-direction.

I f one assigns o x y g e n atoms to t h e ( l / 3 , 2 / 3 , z )

( 2 / 3 , 1 / 3 , 5 ) positions w i t h ζ =

and

0.25, the c a l c u l a t e d p l a t i n u m - o x y g e n

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

b o n d l e n g t h is 2.07 A . T h i s is 0.08 A l o n g e r t h a n is o b s e r v e d i n / ? - P t 0 ( 1 6 ) , or d e r i v e d f r o m S h a n n o n - P r e w i t t r a d i i (14)

2

(note: a l l radii used

i n this d i s c u s s i o n are t a k e n f r o m t h e S h a n n o n - P r e w i t t t a b l e s ) , b u t is reasonable for the m o r e o p e n structure of the a m b i e n t pressure phase. T h e o x y g e n - o x y g e n distances are 2.74 A b e t w e e n layers a n d 3.10 A w i t h i n e a c h layer. F u r t h e r s u p p o r t for the C d l - t y p e structure i n « - P t 0 2

the recent synthesis of t w o a d d i t i o n a l forms of P t 0

2

2

is afforded b y

i n sealed t u b e ex­

p e r i m e n t s via t h e r e a c t i o n K PtCl 2

4

+ KN0

3

-* Pt0

2

+ 3KC1 + NOC1

(1)

H e a t i n g times at 425 ° C w e r e 5 to 25 days. O n e m o d i f i c a t i o n appears to h a v e a u n i t c e l l 3 times the « - P t 0

ο

£-Pt0

Ι­ Ο.

2

c e l l i n the c - d i r e c t i o n , w i t h a =

2

ο to m <

1000

900

800

700 600 500 400 WAVENUMBER C M '

300

200

1

Figure

1.

Infrared

spectra of Pt0

2

phases

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3.11

4.

H O E K S T R A

E T

(1) A and c =

Reaction

A L .

of Platinum

1 2 . 6 0 ( 6 ) A . T h i s f o r m seems to b e r e l a t e d to t h e C d l 2

type III reported by Pinsker (9).

T h e second m o d i f i c a t i o n c a n b e i n d e x e d

o n t h e basis of C d l - t y p e I I w i t h a =

3.10(1) A a n d c =

2

«-Pt0

2

43

Dioxide

8 . 3 2 ( 6 ) A ; the

c e l l is d o u b l e d i n the c - d i r e c t i o n . T h e space g r o u p for this f o r m is

C , - P 6 m c . W i t h c o o r d i n a t e values b a s e d u p o n C d a n d I positions, the 4

6 t

3

P t - O b o n d lengths are a b o u t 2.07 A i n b o t h modifications. s i m p l e a n d m u l t i p l e h e x a g o n a l cells are k n o w n for b o t h C d l

2

T h u s , the

and ambient

pressure P t 0 . 2

/?-Pt0 .

W e h a v e not s u c c e e d e d i n p r e p a r i n g samples of the h i g h

2

pressure f o r m of P t 0

2

s u i t a b l e for single c r y s t a l studies.

analysis of o r t h o r h o m b i c / ? - P t 0

based

u p o n the intensities of d i f f r a c t i o n lines f r o m p o w d e r samples (16).

The

c e l l parameters are a =

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

A structural

has b e e n c a r r i e d out, h o w e v e r ,

2

4.488(3), b =

4.533(3), c =

3.138(2) A .

i n t e n s i t y d a t a c o n f i r m the t e n t a t i v e C a C l - t y p e structure w i t h coordinates χ =

0.281 a n d y =

The

oxygen

2

0.348 to g i v e t w o l o n g P t - O b o n d s of

2.02 A a n d f o u r shorter b o n d s of 1.98 A . T h e i n f r a r e d spectra of a a n d / ? - P t 0

2

are s h o w n i n F i g u r e 1.

The

s i n g l e a b s o r p t i o n m a x i m u m i n a - P t 0 is analogous to that o b s e r v e d w i t h 2

Cdl

T h e strong peaks of / ? - P t 0 are assigned to P t - O a s y m m e t r i c

(11).

2

2

s t r e t c h i n g modes, a n d the w e a k l o w e r f r e q u e n c y b a n d s are a t t r i b u t e d to b e n d i n g m o d e s i n the P t 0

2

lattice. T h e h i g h e r frequencies o b s e r v e d i n

the 0 - P t O s t r e t c h i n g v i b r a t i o n s (750, 720 c m " ) over t h a t i n a - P t 0 1

2

cm )

are consistent w i t h the ^

- 1

lengths i n the β-form.

2

0.1 A shorter platinum—oxygen

The «-Pt0

2

s t r u c t u r e p r o p o s e d b y B u s c h et al. (1)

(580 bond

s p e c t r u m is inconsistent w i t h

the

since the extremely short (1.47 A )

Pt—Ο distance i n the B u s c h s t r u c t u r e w o u l d r e q u i r e a m u c h

higher

s t r e t c h i n g f r e q u e n c y t h a n w e observe for this phase. B o t h modifications of P t 0

are i n s o l u b l e i n hot c o n c e n t r a t e d

2

HN0 , 3

H S 0 , a n d a q u a r e g i a . « - P t 0 , h o w e v e r , dissolves s l o w l y i n hot c o n c e n ­ 2

4

2

t r a t e d H C 1 , m o r e r e a d i l y i n H B r ; / ? - P t 0 is s o l u b l e o n l y i n H B r . 2

T h e r m a l analysis of « - P t 0 at 575 ° C .

2

indicates that o x y g e n e v o l u t i o n

begins

D e c o m p o s i t i o n to the m e t a l occurs i n a single step, a n d is

c o m p l e t e at — 6 0 0 ° C . T h e β-form is s o m e w h a t m o r e stable, w i t h d e c o m ­ p o s i t i o n b e g i n n i n g at 6 0 0 ° C . T h e dta-tga

trace f r e q u e n t l y gives a n i n d i ­

c a t i o n of a two-step process, b u t a l l attempts to isolate or i d e n t i f y a n i n t e r m e d i a t e p r o d u c t h a v e b e e n unsuccessful.

A l l x - r a y p o w d e r patterns

of p a r t i a l l y d e c o m p o s e d samples s h o w e d o n l y t w o phases: P t 0

M0

2

+

2

and Pt.

Pt0

2

T h e r e a c t i o n of p l a t i n u m d i o x i d e w i t h other m e t a l dioxides c a n b e separated into three groups—i.e., c o m p o u n d s w i t h m e t a l - o x y g e n n a t i o n n u m b e r s of 4:2, 6:3, a n d 8:4.

coordi­

W e h a v e i n v e s t i g a t e d o n l y a single

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

44

P L A T I N U M

m/0

G R O U P

Figure 2.

2

2

(Ge0

2

A N D

C O M P O U N D S

Pt02

Cell dimensions of M0

4:2 c o o r d i n a t e d o x i d e , S i 0

M E T A L S

· Pt0

solid solutions

2

also exists i n t h e α-quartz structure

b u t not at h i g h p r e s s u r e ) . W e find n o e v i d e n c e f o r c o m p o u n d f o r m a t i o n or s o l i d s o l u t i o n i n t h e S i 0 - P t 0 2

2

system at 40 k b a n d 1200°C. T h e s i l i c a

p o r t i o n of t h e s a m p l e is c o n v e r t e d to coesite a n d the / ? - P t 0 d i f f r a c t i o n 2

p a t t e r n shows n o m e a s u r a b l e shift i n l i n e positions. M i x t u r e s of P t 0

2

w i t h 10 oxides h a v i n g t h e r u t i l e or a d i s t o r t e d r u t i l e

structure h a v e b e e n i n v e s t i g a t e d . T w o of the 10, M o 0 , a n d W 0 , r e ­ 2

duce P t 0

2

2

to t h e m e t a l a n d are themselves o x i d i z e d to the t r i o x i d e s . N o

e v i d e n c e for f u r t h e r r e a c t i o n b e t w e e n

M0O3

or W 0

3

a n d excess P t 0

2

c o u l d be d e t e c t e d f r o m a n x - r a y i n v e s t i g a t i o n of the p r o d u c t s . S e v e n 6:3 c o o r d i n a t e d d i o x i d e s

(Ti0 , V 0 , Cr0 , Mn0 , 2

2

2

Ge0 ,

2

2

R u 0 , a n d S n 0 ) s h o w r a t h e r s i m i l a r r e a c t i o n t o w a r d s P t 0 , i n that ex­ 2

2

2

tensive s o l i d s o l u t i o n occurs at 40 k b pressure ( 7 5 0 ° to 1 2 0 0 ° C ) w i t h o u t e v i d e n c e of c o m p o u n d f o r m a t i o n . S o m e of the systems w e r e i n v e s t i g a t e d at 25 m / o intervals, others at 12.5 m / o intervals. I n c o m p l e t e m i s c i b i l i t y w a s d e t e c t e d i n o n l y one of the seven, the C r 0 - P t 0 2

2

system. A s i n g l e

p h a s e r e g i o n is f o u n d f r o m — 5 0 to 100 m / o P t 0 , b u t P t 0 2

shows little

2

s o l u b i l i t y i n C r 0 . I t is p o s s i b l e t h a t m o r e d e t a i l e d studies w i l l disclose a 2

s i m i l a r , b u t n a r r o w e r , t w o - p h a s e r e g i o n b e t w e e n 0 a n d 25 m / o P t 0 the M n 0 - P t 0 2

2

2

in

system.

I n e a c h of the seven systems s t u d i e d , the a d d i t i o n of M 0

2

to P t 0

t i a l l y causes a n increase i n the b/a r a t i o of the o r t h o r h o m b i c P t 0

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

2

ini­

phase.

4.

H O E K S T R A

E T

Reaction

A L .

Table II.

2

a

2

2

2

2

2

2

2

2

Sn0 3Sn0 Sn0 3Sn0 Sn0 Sn0 V0 3V0 V0 V0 Ti0 3Ti0 Ti0 Ti0 Ru0 3Ru0 Ru0 Ru0 Mn0 3Mn0 2Mn0 Mn0 3Mn0 Mn0 Mn0 Cr0 3Cr0 Cr0 Cr0

· · · · · ·

Pt0 Pt0 3Pt0 Pt0 5Pt0 3Pt0 7Pt0 Pt0

2

2

2

2

2

2

2

2

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

2

2

2

2

2

· Pt0 · Pt0 · 5Pt0 - 3Pt0 · 7Pt0

2

2

2

2

2

&

2

· Pt0 · Pt0 · 3Pt0

2

2

2

2

2

2

2

· Pt0 · Pt0 · 3Pt0

2

2

2

2

2

2

2

· Pt0 · Pt0 · 3Pt0

2

2

2

2

2

2

2

2

2

2

2

2

2

· Pt0 · Pt0 · Pt0 · 5Pt0 · 3Pt0 · 7Pt0

2

2

2

2

2

2

2

2

2

2

a b

45

Dioxide

M o 2 - P t 0 Cell Dimensions i n Angstroms"

Composition Ge0 7Ge0 3Ge0 5Ge0 Ge0 3Ge0 Ge0 Ge0

of Platinum

· Pt0 · Pt0 · 3Pt0

2

2

2

c

b

— 2.859 4.390 — 2.891(3) 4.410(5) — 2.932 4.432 — 2.969 4.444 — 3.009 4.465 4.514 3.033 4.437 3.069 4.546 4.437 3.102 4.549 4.448 3.138 4.533 4.488 — 3.186 4.737 — 3.182 4.682 — 3.176 4.630 3.172 4.625 4.571 3.162 4.603 4.531 4.574 3.151 4.506 — 2.872 4.517 Tetragonal not measured — 3.051(3) 4.503(5) 3.092 4.553 4.455 — 2.958 4.594 — 3.007(5) 4.585(5) 3.065(5) 4.600(5) 4.506(5) 3.113 4.580 4.479 — 3.105 4.491 — 3.119 4.498 3.129 4.539 4.475 3.137 4.559 4.469 — 2.871 4.396 2.941(5) 4.519(5) 4.368(5) 2.956(3) 4.547(5) 4.377(5) 4.557(5) 3.006(3) 4.382(5) 3.047 4.402 4.571 3.083 4.561 4.428 3.188 4.549 4.459 — 2.918 4.422 2 phases 3.109(3) 4.438(5) 4.564(5) 4.554 3.157 4.465

Error limits are ± 0.002 A except as indicated, e.g., (5). Based on rutile-type cell.

Further M 0

2

a d d i t i o n s e v e n t u a l l y reverse this t r e n d as t h e b/a

ratio

decreases to u n i t y a n d the s o l i d a c q u i r e s the t e t r a g o n a l r u t i l e structure. F i g u r e 2 illustrates t h r e e of the systems: (a) S n 0 - P t 0 2

2

exhibits t e t r a g o n a l

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

46

P L A T I N U M

symmetry over — 5 0 %

2

of the T i C > 2 - P t 0

2

(b)

A N D

and V 0

2

2

systems, a n d ( c )

2

in P t 0

little if or

2

M0 -Pt0 2

mixtures investigated. T h e symmetry relationships i n M 0 - P t 0 2

a r e different f r o m those o b s e r v e d

show

2

mixtures w i t h C r 0

2

T a b l e I I lists the c e l l parameters m e a s u r e d for t h e

2

C O M P O U N D S

T e t r a g o n a l s y m m e t r y is f o u n d

and R u 0 - P t 0

any tetragonal range can be observed Mn0 .

M E T A L S

of t h e c o m p o s i t i o n r a n g e ; G e 0

s i m i l a r s y m m e t r y patterns w i t h P t 0 . over ~ 2 5 %

G R O U P

2

systems

2

b y M a g n e l i a n d coworkers

in

(19)

m i x t u r e s of o t h e r d i s t o r t e d r u t i l e - t y p e structures. I n these systems, tetr a g o n a l structures w e r e o b s e r v e d over the m a j o r p o r t i o n of t h e c o m p o s i t i o n range, w h e r e a s the m a x i m u m extent of t e t r a g o n a l s y m m e t r y is o n l y — 5 0 % i n t h e seven M o - P t 0 u n d e r i n v e s t i g a t i o n h e r e . 2

2

T h e r m a l analysis of M 0 - P t 0 2

s o l i d solutions r e v e a l n o m a r k e d sta-

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

b i l i z a t i o n effect i n those m i x t u r e s c o n t a i n i n g d i o x i d e s of l i m i t e d t h e r m a l s t a b i l i t y , s u c h as C r 0

or M n 0 .

2

2

T h e stable m o r e r e f r a c t o r y

h o w e v e r , i n c r e a s e the s t a b i l i t y of t h e P t 0 tion.

Thus, only 1/3

75Sn0

2

· 25Pt0

2

of the o x y g e n

2

dioxides,

c o m p o n e n t of t h e s o l i d s o l u -

associated

w i t h p l a t i n u m i n the

m i x t u r e is e v o l v e d as the s o l i d s o l u t i o n is h e a t e d

to

1 2 5 0 ° C at 6 ° / m i n u t e . Pb0 .

L e a d dioxide crystallizes i n a rutile structure a n d c o u l d

2

be

e x p e c t e d to s h o w at least p a r t i a l s o l u b i l i t y i n / 3 - P t 0 . U n d e r pressure, 2

however, P b 0

2

converts to a n o r t h o r h o m b i c m o d i f i c a t i o n w h i c h is v i r -

t u a l l y i n s o l u b l e i n P t 0 , a n d represents a n o t a b l e e x c e p t i o n to t h e exten2

sive s o l i d s o l u t i o n r a n g e o b s e r v e d i n r e l a t e d systems f r o m G e 0 - P t 0 2

2

to

Sn0 -Pt0 . 2

2

O f f u r t h e r interest i n t h e l e a d - p l a t i n u m - o x y g e n system is the

ob-

s e r v a t i o n that a 1:1 m i x t u r e of the d i o x i d e s w i l l react at 40 k b pressure a n d at temperatures a b o v e 750 ° C to f o r m a phase i n d e x i b l e as a facecentered cubic structure w i t h a =

5.15(1) A . V e r y little solid solution

occurs o n either side of the 1:1 m e t a l r a t i o since d e v i a t i o n f r o m this r a t i o gives a d i p h a s i c m i x t u r e of t h e c u b i c phase p a r a m e t e r c h a n g e ) a n d either P t 0

2

( w i t h no discernible cell

or P b 0 . 2

T h e r m a l analysis of

the

c u b i c phase has e s t a b l i s h e d t h a t d e c o m p o s i t i o n to P b O a n d P t o c c u r s at 7 4 0 ° C , a n d that 2.5 atoms of o x y g e n are e v o l v e d for e a c h l e a d or p l a t i n u m a t o m . T h e s e d a t a s t r o n g l y suggest t h a t the n e w c o m p o u n d is P b P t 0 , 2

h a v i n g a cubic pyrochlore-type structure w i t h a =

2

7

10.30 A , t w i c e the

apparent unit cell dimension, rather than a disordered

fluorite

structure.

T h i s i n t e r p r e t a t i o n r e q u i r e s the presence of t r i v a l e n t l e a d i n t h e t e r n a r y oxide. A c o m p a r i s o n of its u n i t c e l l d i m e n s i o n w i t h t h a t of the r a r e e a r t h p l a t i n u m pyrochlores

i n d i c a t e s that the p r e s u m e d

Pb(III)

i o n has a

r a d i u s of 1.08 A for a c o o r d i n a t i o n n u m b e r of 8. T h i s is reasonable w h e n compared

w i t h its t r i v a l e n t n e i g h b o r s , T l ( I I I )

at 1.00 A a n d

at 1.11 A .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Bi(III)

4.

H O E K S T H A

E T

Reaction

A L .

1

of Phtinum

1

1

47

Dioxide

1

1

1

4 1 1 li 1 I ι

II 1

ι 11

\

(

J J Sm Pt20 2

7

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

/

VA

1

900

800

2

ι

1

700

Pb Pt 0

ι

600

ι

500

CM"

300

2

2

200

1

Infrared spectra of Pb Pt 0 Sm Pt 0 2

7

ι

400

WAVENUMBER

Figure 3.

2

2

7

and

7

T h e i n f r a r e d s p e c t r u m of P b P t 0 shows a single s t r o n g a b s o r p t i o n 2

2

7

p e a k at 633 c m " w h i c h is assigned to the a s y m m e t r i c s t r e t c h i n g m o d e i n 1

the o c t a h e d r a l o x y g e n c o n f i g u r a t i o n a b o u t p l a t i n u m . T h e peak i n S m P t 0 2

2

7

(a =

comparable

10.31 A ) is f o u n d ( F i g u r e 3 ) at 635 c m " . 1

The

r e m a i n d e r of the P b P t 0 s p e c t r u m consists of three w e a k m a x i m a at 530, 2

2

7

480, a n d 350 c m " . T h e p e a k locations c o r r e s p o n d r e a s o n a b l y w e l l w i t h 1

m a x i m a i n the S m P t 0 2

weaker.

2

7

s p e c t r u m , b u t the p e a k intensities are m u c h

T h e reason f o r this difference is not u n d e r s t o o d at present.

Fluorite Structures.

T h e r e a c t i o n of P t 0

n a t e d m e t a l d i o x i d e s has b e e n i n v e s t i g a t e d . gives a n y i n d i c a t i o n of r e a c t i o n w i t h P t 0 b y w a y of s o l i d s o l u t i o n or c o m p o u n d

2

2

w i t h several 8:4 Neither C e 0

2

coordi­

nor

Th0

formation.

U r a n i u m d i o x i d e is

o x i d i z e d b y P t O o u n d e r these c o n d i t i o n s to t h e h i g h pressure f o r m U0

( 1 5 ) , w i t h n o i n d i c a t i o n of r e a c t i o n b e t w e e n P t 0

3

2

at 40 k b a n d 1 2 0 0 ° C , either

2

and U 0 . 3

of Zir­

c o n i u m d i o x i d e , a d i s t o r t e d fluorite phase, does not react w i t h P t O o u n d e r these e x p e r i m e n t a l c o n d i t i o n s .

M0 2

3

+

Pt0

2

Rare E a r t h Sesquioxides. react ( 3 , 17)

with P t 0

2

O x i d e s of t h e larger t r i v a l e n t m e t a l ions

at h i g h pressure to f o r m a ftnTOnfefefle CfoeffiÎCal

Society Library 1155 16th St. N . W . Washinaton. D. C. In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

20036

48

P L A T I N U M

G R O U P

M E T A L S

A N D C O M P O U N D S

A P t 0 , s i m i l a r to those r e p o r t e d f o r t i n , r u t h e n i u m , t i t a n i u m , a n d sev­ 2

2

7

e r a l o t h e r t e t r a v a l e n t ions.

T r i v a l e n t ions w h i c h f o r m c u b i c p l a t i n u m

p y r o c h l o r e s r a n g e f r o m S c ( I I I ) a t 0.87 A to P r ( I I I ) a t 1.14 A . D i s t o r t e d p y r o c h l o r e structures are f o r m e d b y l a n t h a n u m (1.18 A ) a n d b y b i s m u t h (1.11 A ) . P l a t i n u m d i o x i d e oxidizes S b 0 2

to S b 0

3

2

a t h i g h pressure.

4

T h e i n f r a r e d spectra a n d t h e r m a l s t a b i l i t y o f t h e r a r e e a r t h p l a t i n a t e s h a v e b e e n r e p o r t e d p r e v i o u s l y a n d w i l l n o t b e r e p e a t e d here, e x c e p t t o p o i n t o u t t h e r a t h e r r e m a r k a b l e t h e r m a l s t a b i l i t y o f these

compounds;

d e c o m p o s i t i o n t o t h e r a r e e a r t h sesquioxide a n d p l a t i n u m r e q u i r e s t e m ­ peratures i n excess of 1 2 0 0 ° C . S m a l l e r T r i v a l e n t Ions. M i x t u r e s o f a l u m i n u m , v a n a d i u m , c h r o m i u m , manganese, i r o n , a n d g a l l i u m sesquioxide w i t h P t 0

were investigated

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

f o r possible c o m p o u n d f o r m a t i o n — n o n e w a s f o u n d .

T h e t r i v a l e n t ions

w h i c h h a v e stable tetravalent o x i d a t i o n states—Le., v a n a d i u m , m a n g a ­ nese, a n d c h r o m i u m — a r e o x i d i z e d b y P t 0

to f o r m M 0 - P t 0

2

2

solutions w h i c h h a v e b e e n d i s c u s s e d p r e v i o u s l y .

2

solid

A l u m i n u m , iron, a n d

g a l l i u m sesquioxides s h o w a p a r t i a l s o l u b i l i t y i n t h e 0 - P t O p h a s e to f o r m 2

oxygen-deficient s o l i d solutions. F i g u r e 4 illustrates t h e c h a n g e i n P t 0 u n i t c e l l v o l u m e as a f u n c t i o n of m o l e f r a c t i o n P t . T h e A 1 0 2

3

is less t h a n 3 m / o ( t h e l o w e s t c o n c e n t r a t i o n i n v e s t i g a t e d ) , b u t t h e F e 0 2

s o l u b i l i t y is a p p r o x i m a t e l y 15 m / o . T h e G a 0 2

3

2

solubility 3

s o l u b i l i t y is difficult to

d e t e r m i n e f r o m x - r a y d a t a since v e r y l i t t l e c h a n g e i n c e l l parameters is 65

Fe 0 . 6 4 5

St

6

Go 0.62

4

Al

Ε ο >

0.53

63

ο

Ο) Ο

Cr

**

0.615^-^

c

Μη 0.65

ID

/

62

0.50

0.60

0.70

Figure 4.

Volume change in Pt0

2

1.00

0.90

0.80 Pt/M

+ Pt

unit cell with M O 2

s

addition

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Dioxide

49

observed, b u t the s o l u b i l i t y is e s t i m a t e d to b e 10 m / o .

T h e s o l i d solutions

4.

H O E K S T R A

E T

Reaction

A L .

are a s s u m e d to b e

of Platinum

oxygen-deficient

rather than a c q u i r i n g interstitial

cations since F e ( I I I ) w i t h a n i o n i c r a d i u s (0.645 A ) greater t h a n P t ( I V ) (0.63 A ) b r i n g s a b o u t a n increase i n c e l l v o l u m e , w h i l e G a ( I I I ) (0.62 A ) p r o d u c e s v i r t u a l l y n o change, a n d A l ( I I I ) at 0.53 causes a s h a r p decrease i n c e l l v o l u m e . T h e anomalous effect o b s e r v e d i n the C r 0 2

3

and M n 0 2

3

m i x t u r e s is a t t r i b u t e d to a c o m b i n e d o x i d a t i o n p l u s s o l i d s o l u t i o n r e a c t i o n . O u r x - r a y d a t a i n d i c a t e t h a t c o m p l e t e o x i d a t i o n to C r 0 o c c u r since c e l l parameters o b t a i n e d f r o m C r 0 c o i n c i d e w i t h those d e r i v e d f r o m C r 0 2

ing for P t 0 Mn0

2

+

3

+

2

Pt0

Pt0

2

does not

2

m i x t u r e s d o not

reactants (after correct-

2

u s e d i n o x i d a t i o n of c h r o m i u m ) .

O x i d a t i o n of M n 0 2

3

to

is c o m p l e t e , since c o m p a r a b l e c e l l d i m e n s i o n s are o b t a i n e d f r o m

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

the t w o r e a c t a n t m i x t u r e s .

MO +

Pt0

2

T h e present d i s c u s s i o n w i l l not i n c l u d e results o n reactions of

Pt0

2

w i t h C a O , S r O , or B a O . T h i s p o r t i o n of o u r i n v e s t i g a t i o n has not b e e n c o m p l e t e d a n d w i l l b e r e p o r t e d later. S e v e r a l of the r e m a i n i n g systems n e e d b e m e n t i o n e d o n l y b r i e f l y : P d O shows n o e v i d e n c e of r e a c t i o n w i t h Pt0

2

at h i g h pressure, a n d the r e a d i l y o x i d i z a b l e m o n o x i d e s of manganese,

iron, and t i n reduce P t 0 M Pt0 2

4

to t h e m e t a l .

2

Compounds.

M u l l e r and R o y (5)

h a v e d e s c r i b e d the s y n -

thesis of spinels i n t h e Z n O - P t 0 a n d M g O - P t 0 systems. W e h a v e p r e 2

p a r e d these c o m p o u n d s

2

at h i g h pressure; the u n i t c e l l d i m e n s i o n s are

8 . 5 5 0 ( 2 ) A for Z n P t 0 a n d 8 . 5 2 1 ( 2 ) A for M g P t 0 , i n excellent agree2

4

2

ment w i t h M u l l e r and Roy.

4

A n e x p e r i m e n t at 1 5 5 0 ° C has

produced

b r i g h t y e l l o w o c t a h e d r a of the z i n c s p i n e l w h i c h are s u i t a b l e for single c r y s t a l studies. T h e r m a l analysis of this c r y s t a l l i n e m a t e r i a l indicates that e n d o t h e r m i c d e c o m p o s i t i o n to Z n O a n d P t occurs at 830 ° C . T h e i n f r a r e d spectra of Z n P t 0 2

4

(Figure 5) and M g P t 0 2

4

are c h a r -

acteristic of spinels w i t h three strong a b s o r p t i o n m a x i m a to 200 c m " ; t h e 1

s i n g l e w e a k b a n d n e a r 250 c m "

1

in Z n P t 0 2

4

and M g P t 0 2

4

200 c m " i n most other spinels. W h i t e a n d D e A n g e l i s (20) 1

occurs

below

have shown

that, c o n t r a r y to some p r e d i c t i o n s , inverse spinels s h o u l d not a n d d o n o t h a v e m o r e c o m p l e x spectra t h a n the n o r m a l spinels. Since the t w o types of ions i n the o c t a h e d r a l sites are r a n d o m l y d i s t r i b u t e d , the o n l y result w i l l b e a shift i n the p e a k frequencies r a t h e r t h a n a r e m o v a l of eracy.

degen-

T a b l e I I I lists tentative assignments g i v e n to the m a x i m a i n the

z i n c a n d m a g n e s i u m spinels. T h e y are i n agreement w i t h the conclusions r e a c h e d b y W h i t e a n d D e A n g e l i s i n i n t e r p r e t i n g s p i n e l spectra since i n t e r n a l s t r e t c h i n g frequencies of M g 0 1

t e t r a h e d r a i n a n u m b e r of spinels

4

r a n g e f r o m 690 to 565 c m " , a n d i n Z n 0

4

t e t r a h e d r a f r o m 667 to 555 c m " .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

1

50

P L A T I N U M

Table III. Mg Pt04 655 c m

612 c m

- 1

575 490 240

A N D

C O M P O U N D S

Assignment M e t a l - o x y g e n stretch i n tetrahedron

- 1

565 465 252

Lattice-stretching mode i n v o l v i n g octahedron B e n d i n g mode i n tetrahedron Lattice bending mode τ

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

M E T A L S

Absorption Bands in Platinum Spinels

ZniPtOi

2

G R O U P

900

1

800

700

1

1

600

500

WAVENUMBER

Figure 5.

1

Γ

400 CM

300

200

- 1

Infrared spectra of Zn Pt0 Cd ?tO 2

%

T h e h i g h f r e q u e n c y v i b r a t i o n is not assigned to a P t 0 i n g m o d e because the m i x e d ( M P t ) 0

and

ll

k

6

6

octahedral stretch­

g r o u p i n g is expected to shift the

v i b r a t i o n to a l o w e r f r e q u e n c y . M u l l e r and Roy (8) h a v e assigned t h e S r P b 0 2

h a v e r e p o r t e d the synthesis of C d P t 0 2

4

structure to this n e w c o m p o u n d .

We

and

4

have

p r e p a r e d this c o m p o u n d a n d o b t a i n e d orange l a t h - l i k e crystals at 1550 ° C a n d 40 k b pressure. O u r p o w d e r d a t a o n C d P t 0 are i n agreement w i t h 2

4

the S r P b 0 structure assignment; w e h o p e to r e p o r t a d e t a i l e d s t r u c t u r e 2

4

analysis later. T h e i n f r a r e d s p e c t r u m is presented i n F i g u r e 5. P e a k as­ signments h a v e n o t b e e n a t t e m p t e d since insufficient s t r u c t u r a l d a t a are a v a i l a b l e . T h e r m a l analysis i n d i c a t e s d e c o m p o s i t i o n of C d P t 0 to C d O 2

4

a n d P t at 8 4 0 ° C , f o l l o w e d b y d e c o m p o s i t i o n of C d O a b o v e 1 0 0 0 ° C .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

4.

H O E K S T R A

E T

A L .

Reaction

of Platinum

51

Dioxide

O u r attempts to p r e p a r e c o m p a r a b l e p l a t i n u m spinels of the r e m a i n i n g d i v a l e n t t r a n s i t i o n m e t a l ions h a v e not s u c c e e d e d . W e h a v e i n d i c a t e d that M n O a n d F e O are o x i d i z e d b y P t 0 , b u t n o s p i n e l f o r m a t i o n w i t h 2

C o O , N i O , or C u O c o u l d b e c o n f i r m e d . A p p a r e n t l y these d i v a l e n t ions c a n n o t b e f o r c e d i n t o t e t r a h e d r a l sites against t h e i r o c t a h e d r a l site p r e f e r ence energy.

T h e m i x e d spinels Z n C o P t 0 , Z n N i P t 0 , a n d M g C o P t 0 4

have, however, been prepared.

4

4

I n these c o m p o u n d s , c o b a l t a n d n i c k e l

c a n r e p l a c e the o c t a h e d r a l l y c o o r d i n a t e d z i n c a n d m a g n e s i u m of

the

s i m p l e spinels. MPt 0 3

with P t 0

2

Compounds.

6

A l t h o u g h C o O , N i O , a n d C u O d o n o t react

to f o r m spinels, t h e y d o p a r t i c i p a t e i n reactions w i t h the d i -

o x i d e to f o r m t e r n a r y oxides h a v i n g the g e n e r a l f o r m u l a M P t 0 ; Z n O , 3

6

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

M g O , C d O , a n d H g O also f o r m m e m b e r s of this series. It is a p p a r e n t f r o m the f o r m u l a t h a t not a l l o f the p l a t i n u m is present i n the t e t r a v a l e n t state, a n d t h e reactions i n v o l v e d represent a d e p a r t u r e f r o m those e n c o u n t e r e d i n t h e systems discussed p r e v i o u s l y . A t y p i c a l e q u a t i o n m a y be w r i t t e n 2HgO + 5 P t 0

2

+ P t -> 2 H g P t 0 3

I n o u r i n i t i a l experiments, H g O a n d P t 0

2

(2)

6

w e r e m i x e d i n a 1:1 m o l a r

ratio a n d h e a t e d u n d e r 40 k b pressure to 8 0 0 ° C for 1 h o u r .

A single

phase c r y s t a l l i n e p r o d u c t w a s r e c o v e r e d , p u r i f i e d i n a q u a r e g i a , a n d f o u n d to b e i n d e x i b l e as a h e x a g o n a l c e l l w i t h a =

7.25 A a n d c =

m e a s u r e d p y c n o m e t r i c d e n s i t y is 12.33 g r a m s / c m . i n d i c a t e d that the c o m p o u n d is not H g P t 0

3

5.16 A . T h e

T h e r m a l analysis

3

since d e c o m p o s i t i o n at 650 ° C

is a c c o m p a n i e d b y o n l y a 3 3 . 5 % w e i g h t loss. A c o m p l e t e analysis of the n e w c o m p o u n d gives the f o l l o w i n g percentages: o x y g e n 1 0 . 8 % , m e r c u r y 22.6%, and platinum 66.6%.

T h e c a l c u l a t e d percentages f o r

are: oxygen 1 0 . 9 % , mercury 2 2 . 7 % , a n d p l a t i n u m 6 6 . 4 % .

HgPt 0 3

6

I n this i n -

stance, the P t f o i l e n v e l o p e is n o t i n e r t to the reactants a n d p a r t i c i p a t e s i n the r e a c t i o n . S u b s e q u e n t experiments w i t h g o l d envelopes a n d w i t h p o w d e r e d p l a t i n u m i n the r e a c t i o n m i x t u r e h a v e c o n f i r m e d t h e s t o i c h i o m e t r y g i v e n i n the e q u a t i o n a b o v e . A s i m i l a r c o m p o u n d is f o r m e d i n the C d O - P t 0 s y m m e t r y is p s e u d o h e x a g o n a l o r t h o r h o m b i c .

system, b u t the

2

I n addition, certain weak

lines d i s c e r n i b l e i n the p o w d e r p a t t e r n i n d i c a t e that a l a r g e r c e l l m u s t b e chosen. A tentative i n d e x i n g of H g P t 0 3

6

and C d P t 0 3

6

w h i c h gives r e a -

sonable agreement i n intensities places these c o m p o u n d s i n space g r o u p Immm

— D

25

2h

w i t h H g or C d i n positions 2a a n d 2c, d i v a l e n t p l a t i n u m

i n positions 2b a n d 2d, tetravalent P t i n 8k, 0 / i n 8m, a n d O

n

and

O

i n

i n 8n. A l t h o u g h w e h a v e chosen a r b i t r a r y values for the o x y g e n c o o r d i nates b a s e d o n a k n o w l e d g e of c a t i o n r a d i i , w e h a v e not a t t e m p t e d to v e r i f y the structure.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

52

P L A T I N U M

3

Dimensions Compound HgPt 0 CdPtsO ZnPtsOe MgPtsOe NiPt 0 CoPtaOe 3

6

e

6

Table V .

6

A N D C O M P O U N D S

Compounds

in A ( ± 0.005)

a

b

c

10.334 10.189 9.953 9.928 9.919 9.925

7.264 7.215 7.131 7.115 7.109 7.084

6.286 6.327 6.287 6.304 6.234 6.234

Powder D a t a for M g P t O ( C r Radiation)

orthorhombic Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

M E T A L S

U n i t Cell Dimensions of M P t 0

Table I V .

3

G R O U P

3

e

a = 9.928, b = 7.115, c = 6.804 A

hkl

d(A)

lobtd

hkl

d

/

110 200 020 002 310 220 112 202 400 022 130 312 222 420 402 330 510 132 040 422 240 332 512

5.733 4.916 3.527 3.132 2.984 2.878 2.754 2.651 2.470 2.350 2.298 2.168 2.123 2.025 1.945 1.921 1.907 1.855 1.774 1.706 1.669 1.639 1.631

20 10 5 1 15 100 15 65 50 55 1 5 10 5 5 10 5 5 60 85 5 5 5

004 042 114 620 242 602 440 150 314 224 532 622 404 442 152 712 424 800 334 352 044 820 260

1.573 1.544 1.518 1.4969 1.4760 1.4626 1.4433 1.4065 1.3949 1.3817 1.3681 1.3528 1.3286 1.3127 1.2842 1.2718 1.2459 1.2402 1.2188 1.2061 1.1796 1.1708 1.1532

45 5 10 70 85 65 70 5 5 80 10 10 60 5 30 30 5 80 35 20 100 20 100

A n a l o g o u s c o m p o u n d s are o b t a i n e d w i t h t h e t r a n s i t i o n m e t a l m o n oxides. H e r e a g a i n , o u r e a r l y results suggested a l o w e r p l a t i n u m content f o r t h e o r t h o r h o m b i c phases, b u t a r e c o g n i t i o n o f t h e p a r t i c i p a t i o n of P t m e t a l i n t h e r e a c t i o n l e d t o a r e v i s i o n of t h e c o m p o s i t i o n .

Subsequent

experiments at t h e s t o i c h i o m e t r y g i v e n b y E q u a t i o n 2, together

with

c h e m i c a l analyses of t h e p u r i f i e d p r o d u c t s , h a v e c o n f i r m e d t h e M P t 0 3

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6

4.

HOEKSTRA ET AL.

Reaction of Platinum Dioxide

53

formulation for the entire series. Cell dimensions for the six compounds are given in Table IV and powder data for the magnesium compound in Table V. The copper compound is not listed since it is not isostructural with the other members of the series, presumably owing to a Jahn-Teller distortion. Muller and Roy (7) have reported some structural data on CuPt O . Thermal analysis of the MPt 0 series indicates a somewhat dimin­ ished stability relative to the M Pt0 compounds; decomposition to MO and Pt occurs at 650°-700°C, which is about 150° lower than the spinel decomposition temperature. 3

e

3

2

6

4

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004

Acknowledgment We are indebted to B. S. Tani for assistance in acquiring the x-ray daita, and to Vaughn Leigh, Fleet Rust, and John Beres for their help with some of the experiments at high pressure.

Literature Cited (1) Busch, R. H., Galloni, E. E., Raskovan, J., Cairo, A. E., Anais Acad. Brasil. Cienc. 1952, 24, 185. (2) Hoekstra, H. R., Inorg. Chem. 1966, 5, 754. (3) Hoekstra, H. R., Gallagher, F., Inorg. Chem. 1968, 7, 2553. (4) Hoekstra, H. R., Siegel, S., Inorg. Chem. 1968, 7, 141. (5) Muller, O., Roy, R., Mater. Res. Bull. 1969, 4, 39. (6) Muller, O., Roy, R.,J.Less Common Metals 1968, 16, 129. (7) Muller, O., Roy, R.,J.Less Common Metals 1969, 19, 209. (8) Muller, O., Roy, R.,J.Less Common Metals 1970, 20, 161. (9) Pinsker, Z. G.,J.Phys. Chem. USSR 1941, 15, 559. (10) Randall, J. J., Ward, R.,J.Am. Chem. Soc. 1959, 81, 2629. (11) Randi, G., Atti Accad. Naz. Lincei, Rend., Classe Sci. Fis.Mat.Nat 1966, 41, 197. (12) Scheer, J. J., Van Arkel, A. E., Hayding, R. D., Can. J. Chem. 1955, 33, 683. (13) Shannon, R. D., Solid State Comm. 1968, 6, 139. (14) Shannon, R. D., Prewitt, C. T., Acta Cryst. 1969, B25, 925. (15) Siegel, S., Hoekstra, H., Sherry, E., Acta Cryst. 1966, 20, 292. (16) Siegel, S., Hoekstra, H. R., Tani, B. S.,J.Inorg. Nucl. Chem. 1969, 31, 3803. (17) Sleight, A. W., Mater. Res. Bull. 1968, 3, 699. (18) Statton, W. O.,J.Chem. Phys. 1951, 19, 40. (19) Sundholm, Α., Anderson, S., Magneli, Α., Marinder, B., Acta Chem. Scand. 1958, 12, 1343; Marinder, B., Magneli, Α., ibid., 1958, 12, 1345. (20) White, W. B., De Angelis, Β. Α., Spectrochim. Acta 1967, 23A, 985. RECEIVED December 16, 1969. Work performed under the auspices of the U. S. Atomic Energy Commission.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

5

Nitrido Complexes of the Platinum G r o u p Metals

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

M. J. CLEARE and F. M. LEVER Johnson, Matthey & Co., Ltd., Research Laboratories, Wembley, Middlesex, England W. P. GRIFFITH Inorganic Research Laboratories, Imperial College of Science & Technology, London, S.W. 7, England

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M—N—M unit. They have the stoichiometries [MNX(HO)] and [MN(NH)Y] (M = Os, Ru; X = Cl, Br; Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal—oxo complexes i discussed briefly. 3-

2

8

1

2

3+

2

2

38

2

3

'"J" he nitride ion, N ", is a strong 7r-donor ligand and, as such, one expects tofindit complexed with a metal in a relatively high oxidation state, similar to oxide andfluoridein their complexes. Of the six platinum group metals, nitrido complexes are known at present only for osmium, ruthenium, and iridium. These are shown in Table I. The terminal complexes of osmium have been known for many years, and we intend in this paper to discuss them only briefly, concentrating in more detail on the binuclear species of osmium and ruthenium, which we have been studying recently. The trinuclear complexes of iridium and osmium are discussed in the light of recent spectroscopic data. A heterometallic species, (PEt Ph) Cl ReNPtCl (PEt3), with a nitrogen bridge between a platinum and a rhenium atom has been described recently by Chart and Heaton (2), but will not be discussed here. A

2

2

2

54 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3

5.

C L E A R E

E T

Nitrido

A L .

55

Complexes

Terminal Osmium Nitrido Complexes T h e s e c o m p o u n d s h a v e b e e n k n o w n for m a n y years a n d the p r e p a r a ­ t i v e m e t h o d s are i n d i c a t e d i n T a b l e I I . P o t a s s i u m o s m i a m a t e , K [ O s ( V I I I ) 0 N ] , is p r e p a r e d b y the a d d i t i o n 3

of aqueous a m m o n i a to a s o l u t i o n of o s m i u m tetroxide, O s 0 , i n c a u s t i c 4

potash solution (6). Table I.

X - r a y studies s h o w t h e m o l e c u l e to b e b a s i c a l l y

N i t r i d o Complexes of the Platinum Metals Osmium

Terminal

Os(VIII) [Os0 N]Os(VI) [ O s N X ] - [ O s N X H 0 ] (X = Cl,Br,CN,l/2 X ) 3

5

2

5

4

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

0

Bridging

Os(IV) [ O s N X ( H 0 ) ] - ( X = Cl,Br) [Os N(NH )8X ] (X = Cl,Br,I,NCS,N ,N0 ) 2

8

2

2

3

2

3

2

3 +

3

Trinuclear

3

Os N 0 H i 3

7

9

2

Ruthenium Bridging only

[Ru(IV),N X (H 0) ] -(X = Cl,Br,NCS) [Ru(IV) N(N0 ) (OH) (H 0) ] " [ R u ( I V ) N ( N H ) X ] + ( X = Cl,Br,NOa) [ R u ( I V ) N ( N H ) (H O) X ] ( X = C1,NCS,N ) 8

2

2

2

2

3

2

3

2

6

2

8

3

2

2

3

3

2

6

a

3

2 +

3

Iridium Trinuclear only:

[Ι^Ν^Ο,ΜΗ,Ο);,] [Ir N(S0 ) (OH) ] [Ir N C1 (H 0) ] " 4

3

4

3

6

3

1 2

Table II.

2

3

7

4

Terminal Osmium N i t r i d o Complexes Os(VIII)

Os0

4

+

O H

9

+

N H -> [ O s 0 N ] " + 3

3

2H 0 2

P o t a s s i u m o s m i a m a t e forms pale y e l l o w c r y s t a l s . Molecular structure : distorted tetrahedral ν Os = Ν 1021 c m - . 1

Os(VI) [Os0 N]- + Χ " + 3

6 H X -> [Os Ν X ] - + X 2

5

(X =

2

+

3H 0 2

Cl,Br)

T h e s e complexes t e n d t o lose t h e l i g a n d t r a n s t o the n i t r i d e t o give (Os N X H 0 ) ~ ( X = B r , C N , y ox) i n aqueous s o l u t i o n ; ν O s = N ~ 1080 cm . 4

2

2

- 1

M o l e c u l a r s t r u c t u r e : d i s t o r t e d o c t a h e d r a l ( C ) w i t h the o s m i u m a t o m s l i g h t l y o u t of the X p l a n e t o w a r d s t h e n i t r i d e (in the case of [ O s N C l ] ) . 4r

4

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

5

3 -

56

P L A T I N U M

G R O U P

M E T A L S

t e t r a h e d r a l , a l t h o u g h s o m e w h a t d i s t o r t e d (12). frequency

1

(X =

complexes

of t y p e

1 5

N substitution

[ O s ( V I ) N X ] - or 5

C O M P O U N D S

T h e Os==N s t r e t c h i n g

is at 1021 c m " , w h i c h shifts to 993 o n

Os(VI)

A N D

(16).

[Os(VI)NX4H 0]"

2

2

C l , B r , C N , ^ox) are m a d e b y t h e a c t i o n of t h e a p p r o p r i a t e a c i d

H X o n p o t a s s i u m o s m i a m a t e (6, 11).

T h e t e n d e n c y to lose the l i g a n d

trans to t h e n i t r i d e a n d to substitute a w a t e r m o l e c u l e is s o m e e v i d e n c e of a trans l a b i l i z i n g effect of n~donor l i g a n d s . X - r a y studies s h o w a d i s ­ t o r t e d o c t a h e d r a l s t r u c t u r e w i t h the o s m i u m a t o m s l i g h t l y out of the p l a n e of t h e e q u a t o r i a l X atoms t o w a r d s the n i t r i d e ( I ) . stretching

frequency

is a r o u n d 1080 c m "

T h e Os==N

i n s u c h complexes.

(11)

1

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

Binuclear Nitrides of Osmium and Ruthenium I n g e n e r a l , t h e r e is a s i m i l a r r a n g e of complexes

for each metal,

b o t h b e i n g i n t h e o x i d a t i o n state ( I V ) . Anionic Complexes.

T h e p r e p a r a t i o n of these c o m p o u n d s

is i n d i ­

c a t e d i n T a b l e I I I . T h e p r o d u c t of t h e r e a c t i o n of ( N H ) [ O s C l ] w i t h 4

2

6

c h l o r i n e gas at 4 0 0 ° C w i l l dissolve i n d i l u t e h y d r o c h l o r i c a c i d ; f r o m this Table III.

Binuclear Osmium and Ruthenium N i t r i d o Complexes Anionic

Complexes

Cli

(NH ) 4

2

[Os CI,]

+ [Os NCl (H 0) ] 400°C then H C 1 2

8

2

3

2

[Ru N C1 (H 0) ] 2

8

2

2

3

[RuN(OH) · nH 0] 6

NH

3

2

Aq./OHQ

[Ru0 ] 4

2

HBr [Ru N(OH) 2

6

5

2

2

[Ru N(OH) · n H 0 2

[Ru N Br (H 0) ] -

· nH 0]

2

8

2

3

2

HC1 + [Ru N C1 (H 0) ] 2

8

2

3

2

NC93 Ν0 θ 2

[Ru N(N0 ) (OH) (H 0) ] 2

2

6

2

2

2

3

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

5.

C L E A R E

E T

ΝUndo

A L .

57

Complexes

s o l u t i o n , salts of the t y p e M ( I ) [ O s ( I V ) 2 N C l ( H 0 ) 2 ] 3

tated ( 5 ) .

8

can be p r e c i p i ­

2

T h e analogous r u t h e n i u m complexes

m a y be prepared

by

r e a c t i o n of K [ R u ( N O ) C l ] w i t h stannous c h l o r i d e i n h y d r o c h l o r i c a c i d 2

solution (4).

5

O t h e r p r o d u c t s are f o r m e d i n this r e a c t i o n , i n p a r t i c u l a r a

n i t r o s y l c o m p l e x c o n t a i n i n g c o o r d i n a t e d S n C l " , w h i c h is s t i l l u n d e r i n ­ 3

vestigation. A d d i t i o n of a l k a l i to a n aqueous s o l u t i o n of [ R u ( I V ) N C l ( H 0 ) ] ~ 2

y i e l d s a b r o w n gelatinous p r e c i p i t a t e of R u N ( O H ) 2

8

2

2

3

· n H 0 which will

5

2

redissolve i n h y d r o c h l o r i c a c i d to regenerate the o r i g i n a l c o m p l e x . h y d r o x y species m a y b e p r e p a r e d d i r e c t l y b y the a c t i o n of

This

formaldehyde

w i t h K [ R u ( N O ) C l ] i n a l k a l i n e s o l u t i o n , or b y r e a c t i o n of p o t a s s i u m 2

5

r u t h e n a t e , K [ R u 0 ] w i t h excess aqueous a m m o n i a . H y d r o b r o m i c a c i d 2

4

o n t h e h y d r o x y c o m p l e x y i e l d s [ R u N B r ( H 0 ) ] ~ , w h i l e the a c t i o n of Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

2

8

2

3

2

excess t h i o c y a n a t e o n a h y d r o c h l o r i c a c i d s o l u t i o n of the h y d r o x i d e gives [Ru N(NCS) (H 0) ] ". 2

8

2

P o t a s s i u m n i t r i t e reacts w i t h a n aqueous s o l u ­

3

2

t i o n of [ R u N C l ( H 0 ) ] - t o give [ R u N ( N 0 ) ( O H ) ( H 0 ) ] - . 2

8

2

3

2

2

2

6

2

2

f r a r e d s p e c t r a i n d i c a t e that b o t h of t h e l a t t e r l i g a n d s ( N 0

In­

3

2

and N C S )

2

are N - b o n d e d to the m e t a l ( 5 ) . M o l a r conductances of these a n i o n i c complexes i n aqueous s o l u t i o n are i n i t i a l l y close to the values e x p e c t e d for 3:1 electrolytes, b u t o n l o n g s t a n d i n g or o n h e a t i n g t h e conductances increase g r e a t l y , a n d there is a p a r a l l e l decrease i n the p H of t h e s o l u t i o n . W e assume t h a t this results f r o m r e p l a c e m e n t of the h a l o l i g a n d s b y a q u o groups a n d loss of a p r o t o n f r o m the w a t e r l i g a n d s . T h e effect is less m a r k e d for the o s m i u m c o m ­ plexes t h a n for r u t h e n i u m , p r e s u m a b l y because of the greater inertness of t h i r d - r o w elements t o w a r d s s u b s t i t u t i o n ( 5 ) . C a t i o n i c C o m p l e x e s . O n e series of a m m i n e complexes has b e e n f o u n d for o s m i u m ( [ O s N ( N H ) V ] 2

X ] 2

3 +

and

3

8

2

3 +

) a n d two for r u t h e n i u m ( [ R u N ( N H ) 2

[Ru N(NH ) (H 0)X ] 2

3

6

2

3

2 +

).

3

T h e preparative methods

8

are

indicated i n Table I V . R e a c t i o n of s o d i u m chloroosmate

Na [OsCl ] 2

w i t h aqueous

6

am­

m o n i a at ~ 1 0 0 ° C i n a C a r i u s t u b e y i e l d s [ O s N ( N H ) C l ] C l . A n o t h e r 2

3

8

2

3

m e t h o d is the r e a c t i o n of a m m o n i a w i t h K [ O s N C l ( H 0 ) ] . T h e p r o d ­ 3

2

u c t w i l l react w i t h excess X " i o n to g i v e

8

2

2

[Os N(NH ) X ]X 2

3

8

2

(X

3

=

B r " , I " , N C S " , N " , N 0 " ) after short r e f l u x i n g i n aqueous s o l u t i o n . Salts of 3

3

the f o r m [ O s N ( N H ) X ] Y m a y b e p r e p a r e d m e t a t h e t i c a l l y w i t h Y " i o n 2

3

8

2

3

i n the c o l d , suggesting t h a t o n l y t w o of the five X groups are c o o r d i n a t e d . T h e r e a c t i o n of aqueous a m m o n i a o n K [ R u N X ( H 0 ) ] gives a 3

m i x t u r e of Cl,Br).

[Ru N(NH ) X ]X 2

3

8

2

3

2

8

2

2

and [ R u N ( N H ) ( H 0 ) X ] X 2

3

6

2

3

(X

2

T h e f o r m e r y i e l d s species of the f o r m [ R u N ( N H ) X ] Y 2

metathesis i n the c o l d w i t h Y " i o n ( Y =

3

8

2

3

— on

B r , I , N C S , N , N 0 " ) , while boiling 3

3

w i t h a n excess of c e r t a i n l i g a n d s results i n a m m i n e r e p l a c e m e n t c o n v e r s i o n to a h e x a m m i n e species—i.e., [ R u N ( N H ) ( H 0 ) Y ] Y 2

3

6

2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3

and 2

(Y

58

P L A T I N U M

Table IV.

M E T A L S

A N D

C O M P O U N D S

Binuclear Osmium and Ruthenium Nitrido Complexes Cationic NH

[Os X ] " 6

Aq.

3

2

NH 2

Complexes

> [Os N(NH ) X J X 100°C,Carius (X = Cl,Br) tube

2

[Os NCl (H 0) ] 8

2

[Os N(NH ) 2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

G R O U P

3

3

2

2

8

3

Aq.

3

> [Os N(NH ) 100°C, C a r i u s tube

Cl ] +

8

3

3

2

3

Excess X ~ > [Os N(NH ) Reflux i n a q . soin 2

3

C1 ]C1

8

2

3

X ] +

8

2

3

(X = Br,I,NCS,N ,N0 ) 3

[Ru N(NH ) 2

NH [Ru N 2

3

3

3

C1 ]C1

8

2

2

Aq.

X (H 0) ] ~ 8

2

2

3

Heat [Ru N(NH ) (H 0)Cl ]Cl 2

Figure

1.

Structure

of the anion in

3

6

2

3

2

K [Ru NCl (HgO) ] 3

2

8

2

= N " , N C S " , N 0 " ) . I t appears t h a t other ligands—e.g., N 0 " — w i l l l e a v e t h e c o m p o u n d as a n o c t a m m i n e . Species of t h e t y p e [ R u N ( N H ) ( H 0 ) Y ] Z m a y b e m a d e b y metathesis w i t h Z " i n t h e c o l d ( Z = C 1 , I ) . 3

2

3

2

2

3

2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

3

6

5.

C L E A R E

E T

Nitrido

A L .

59

Complexes

M o l a r c o n d u c t a n c e s for the o s m i u m a n d r u t h e n i u m o c t a m m i n e s i n aqueous s o l u t i o n w e r e close to the values e x p e c t e d f o r 3:1 (.—360 m h o s c m )

electrolytes

b u t rose o n s t a n d i n g or h e a t i n g to g i v e final values

2

nearer that e x p e c t e d for a 5:1 electrolyte ( ^ 6 0 0 m h o s c m ) .

T h i s is p r e ­

2

s u m a b l y because of trans a q u a t i o n ; the effect w a s a g a i n less m a r k e d for o s m i u m . S i g n i f i c a n t l y , a l l the h a l o g e n i n the h a l o species [ R u N ( N H ) 2

3

Χ 2 ] Χ δ c o u l d be p r e c i p i t a t e d w i t h silver n i t r a t e f r o m h e a t e d

8

solutions.

C o n d u c t i v i t i e s for the h e x a m m i n e s also v a r i e d s o m e w h a t w i t h t i m e , b u t i n i t i a l values w e r e l o w e r t h a n for the o c t a m m i n e s presence of a 2:1 electrolyte (240 m h o s c m )

and indicated

the

(5)

2

A n x-ray s t r u c t u r a l d e t e r m i n a t i o n has b e e n c a r r i e d out

Structure.

on K [ R u 2 N C l ( H 0 ) 2 ] 3

8

(3)

2

a n d the results are d e p i c t e d i n F i g u r e 1.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

T h e a n i o n has a l i n e a r skeleton w i t h the e i g h t e q u a t o r i a l c h l o r i n e atoms e c l i p s e d so that the o v e r - a l l i d e a l i z e d s y m m e t r y of the a n i o n is D .

Each

4h

r u t h e n i u m a t o m is d i s p l a c e d 0.19 A out of the C l n i t r o g e n atom.

4

plane toward

the

S u c h a d i s p l a c e m e n t of m e t a l atoms t o w a r d s a 7r-donor

l i g a n d has b e e n o b s e r v e d i n other complexes, s u c h as K [ R e O C l i ] 4

2

(18)

0

a n d (Ph^As) [ M o O B r H 0 ] ( 7 ) , as w e l l as K [ O s N C l ] ( I ) , w h i c h has 4

2

2

5

b e e n m e n t i o n e d p r e v i o u s l y . I t has b e e n suggested that this arises m a i n l y f r o m the r e p u l s i o n b e t w e e n the n i t r o g e n a n d c h l o r i n e l i g a n d s w i t h i n t h e molecule. S p e c t r a of

Vibrational Spectra.

t y p i c a l complexes are l i s t e d i n

T a b l e s V a n d V I . T h e c o m p o u n d s e x h i b i t s i m i l a r spectra,

suggesting

that t h e y a l l h a v e the same b a s i c structure. T h e m a i n features a r e : ( a ) T h e presence of a strong sharp b a n d i n the i n f r a r e d i n the r a n g e 1 0 5 0 - 1 1 3 0 c m " , not o b s e r v e d i n t h e R a m a n . T h i s b a n d is l i t t l e c h a n g e d i n f r e q u e n c y o n d e u t e r i a t i o n , b u t shifts d o w n w a r d b y s o m e 30 c m " o n 1

1

Table V .

Vibrational Spectra of Bridging Nitrido Complexes—Anionic Species

(M NX (H 0) y2

s

K (Os N 3

2

VM N

2

2

C1 (H 0) )

2

8

2

R

2

aS

—

2

8

267(10)

J315(4) /295(2) 303s b r

185w

329(4)

J301(10) (294(4)

200w

I R 1137 v s ° I R 1135 v s K (Ru N 3

C1 (H 0) )

2

8

2

R

2

—

R — I R 1078 v s a

a

K (Ru 3

a

2

1 5

N

C1 (H 0) ) 8

2

2

%X-M-X

V MN

330(4)p (315s /289m

I R 1080 v s I R 1046 vs

—

{315s /289m

Indicates aqueous solution measurement.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

60

P L A T I N U M

Table V I .

3 s

2

3

2

2

8

3

(Os N(ND ) C1 )C1 2

3

2

8

3

(Ru N(NH ) C1 )C1 2

3

2

8

a

R — I R 1104 v s

299(10)

2

3

R — I R 1101 v s

286(10)

8

3

267(1) 260s b r

286(3) 282m

430w 440w

254(1) 240s b r

278m 281m

J496(3) 1475(1) 465w

265w b r

280w

258m br

2 8 0 m sh

440vw 430w

250(1) 245s b r

273w 2 7 7 m sh

— 354(1)

R

—

IR

1055

—

R — I R 1054 v s

339(10)

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

2

C O M P O U N D S

455w 465w

—

3

(Ru N(ND ) C1 )C1

A N D

%M—NH

VM-NH

VM N *

2

(Os N(NH ) C1 )C1

M E T A L S

Vibrational Spectra of Bridging N i t r i d o Complexes—Cationic Species

(M N(NH ) X y+ 2

GROUP

—

Figure 2. Bonding in Ο—Ru and Ru—Ν—Ru tems

Ru— sys­

Diagram shows 4 d « - 2 p - 4 c L overlap. There will be a sim­ ilar 4 d x y - 2 p y - 4 d x y ΟΌβ^Ρ ΰ ί right angles to the plane of the paper. e

B

—

-4d =4d

x

z

y 2

EMPTY PAIRED METAL ELECTRONS PAIRED LIGAND ELECTRONS

•U

Figure

3.

Bonding

in bridging

nitride

complexes

The M.O. diagram indicates the formation of two sets of 3-center molecular orbitals with the metal d electrons paired in the nonbonding orbitals

N substitution i n [ O s N ( N H ) B r ] B r and K [ R u NCl (H 0) ]. T h i s b a n d w e h a v e assigned to v M N> the a s y m m e t r i c M — Ν — M stretch. T h i s m o d e consists almost e n t i r e l y of n i t r o g e n m o v e m e n t a n d is expected to o c c u r i n the same r e g i o n as t h e t e r m i n a l m e t a l n i t r i d e stretches. ( b ) T h e presence of a s t r o n g , s h a r p , p o l a r i z e d R a m a n b a n d near 350 c m " f o r the r u t h e n i u m complexes a n d 280 c m " for the o s m i u m c o m 1 5

2

1 5

1 5

3

as

1

8

2

3

3

2

1 5

8

2

1

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

2

5.

C L E A R E

E T

Nitrido

A L .

61

Complexes

plexes, w h i c h w e assign to t h e s y m m e t r i c M — Ν — M s t r e t c h , V M N - T h e s e bands are n o t o b s e r v e d i n t h e i n f r a r e d spectra. T h e y shift d o w n w a r d some 13 c m " o n d e u t e r i a t i o n of t h e a m m i n e complexes, b u t this is l i k e l y to b e c a u s e d b y strong c o u p l i n g of V N ( a totally symmetric m o d e ) w i t h the s y m m e t r i c m e t a l a m m i n e stretches a n d deformations h a v i n g t h e same s y m m e t r y species (A ), together w i t h a slight effect a r i s i n g f r o m t h e greater mass of d e u t e r i u m . H e r e t h e m o d e consists m a i n l y of m e t a l m o v e ­ m e n t ; this is c l e a r l y s h o w n b y t h e effect of t h e extra mass of o s m i u m . T h e g e n e r a l l a c k of c o i n c i d e n c e b e t w e e n R a m a n a n d i n f r a r e d bands a n d , i n p a r t i c u l a r , t h e fact that t h e R a m a n - a c t i v e V M N a n d i n f r a r e d - a c t i v e v M N a r e i n a c t i v e i n the i n f r a r e d a n d R a m a n , respectively, strongly s u g ­ gest t h e presence of a center of s y m m e t r y . T h u s , as i n [ R u N C l ( H 0 ) 2 ] ~ t h e a q u o groups l i e trans to the n i t r i d e g r o u p , i t is l i k e l y t h a t the X groups i n [ M N ( N H ) X ] w i l l b e p l a c e d s i m i l a r l y ( 5 ) . S

2

1

S

M

2

lg

S

as

2

2

2

8

3

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

2

3

8

2

3 +

E l e c t r o n i c S p e c t r a . A l l these complexes are d i a m a g n e t i c as a result of t h e 7r-bonding, w h i c h is s h o w n i n F i g u r e 2. O f t h e f o u r m e t a l d electrons o n e a c h r u t h e n i u m a t o m ( R u ( I V ) d ) , t w o {d ,d ) w i l l p a i r u p i n t h e n o n b o n d i n g m o l e c u l a r o r b i t a l of t h e set p r o d u c e d b y t h e 3-center o v e r l a p b e t w e e n t h e d a n d d orbitals o n e a c h m e t a l a t o m , a n d t h e 2p a n d 2p orbitals o n t h e n i t r i d e . T h e l o w e r energy n i t r i d e electrons w i l l p a i r i n the b o n d i n g m o l e c u l a r orbitals ( F i g ­ ure 3 ) . T h e r e m a i n i n g t w o electrons p e r r u t h e n i u m a t o m are p a i r e d i n t h e 4 dy o r b i t a l w h i c h remains essentially n o n b o n d i n g . I t is a consequence of this b o n d i n g scheme that t h e M — Ν — M g r o u p s h o u l d b e l i n e a r a n d that t h e e q u a t o r i a l ligands s h o u l d b e i n t h e e c l i p s e d (D ) rather than the staggered ( D ) positions. 4

xy

xz

xy

y

xz

z

Z

4h

4 d

Figure

4.

Electronic

spectra of some bridging complexes

nitrido

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

62

P L A T I N U M

G R O U P

5 0 s 0 + 7NH (llq) I l ^ L ^ 4

M E T A L S

A N D

C O M P O U N D S

Os N 0 H |

3

3

7

9

2

ORIGINAL FORMULATION HN 3

\/

OH

HO

—Os

/\

IR. BANDS

HN

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

NH

\/

3

= O s = 0

/\

OH

2

OH

NH

3

AT 1087, 1025, 970cm SHIFT

1053,997, 935cm

NEW

Ν

/\

OH

3

HO

\/

0 = O s = N HN

OH

, 5

ON

N

TO

SUBSTITUTION

FORMULATION HO

OH

v

\/

H O — Os = H^N

Figure

H^l

\/

HOI

Ν — Os

\>H

5.

OH

\/

Ν =

N^^NH

3

Os

HO^

NH

3

OH ^OH

Trinuclear Os(VI) nitndo plex

com­

T h e electronic spectra (350-190 τημ) of three of these complexes are s h o w n i n F i g u r e 4. Jorgensen a n d O r g e l (14)

h a v e suggested that s i m i l a r

bands observed i n K [ R u O C l i ] arise f r o m transitions f r o m the h a l o g e n 4

2

0

l i g a n d s to the a n t i b o n d i n g m o l e c u l a r o r b i t a l f r o m the 3-center b o n d . f o l l o w this assignment for the

[M NX Y2]

system, a l t h o u g h i t is n o t

8

2

We

s t r i c t l y isolectronic w i t h [ R u O X i ] " . T h e R u — O — R u a n d R u — N — R u 2

groupings

are, h o w e v e r ,

4

0

isolectronic.

The

energy

of t h e a n t i b o n d i n g

m o l e c u l a r o r b i t a l is d e t e r m i n e d l a r g e l y b y the extent of the R u — Ο — R u or R u — Ν — R u π-bonding.

T h e b a n d s are seen near 400 τημ for

O C l i o ] " a n d at 397 a n d 330 m ^ ^ ^ H ) [ O s O C l i o ] . 4

4

2

are h i g h e r i n energy (e.g., K [ O s N C l ( H 0 ) ] , 273 τημ; 3

( H 0 ) ] , 294 τημ), 2

2

2

8

2

[Ru 2

In nitride they

2

2

K [Ru NCl 3

2

8

i n d i c a t i n g that M - N ττ-bonding is stronger t h a n for

M - O i n these b i n u c l e a r systems.

Trinuclear Osmium Complex T h e final p r o d u c t of the r e a c t i o n of l i q u i d a m m o n i a w i t h O s 0 the e m p i r i c a l f o r m u l a O s N 0 H i (17,20). 3

r e d s p e c t r u m of the

15

7

9

2

4

has

W e h a v e s t u d i e d the i n f r a ­

N - s u b s t i t u t e d c o m p o u n d a n d p r o p o s e structure I I

( F i g u r e 5) rather t h a n structure I, w h i c h was suggested o r i g i n a l l y . B a n d s at 1087, 1025, a n d 970 c m " shift to 1053, 997, a n d 935 o n N - s u b s t i t u t i o n 1

15

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

5.

C L E A R E

E T

Nitrido

A L .

63

Complexes

a n d m a y b e assigned to O s — Ν — O s o r O s — Ν s t r e t c h i n g modes. T h e n e w f o r m u l a t i o n accounts f o r t h e o b s e r v a t i o n t h a t o n l y t w o molecules of a m ­ m o n i a are released o n h e a t i n g w i t h a l k a l i , since t w o of the a m m i n e groups are i n a different e n v i r o n m e n t f r o m the other t w o (5), a n d thus p r e s u m ­ a b l y h a v e different stabilities i n respect to m e t a l - n i t r o g e n b o n d strengths.

Trinuclear Iridium Complexes T h e reaction of ( N H ) [ I r C l ] w i t h b o i l i n g sulfuric acid yields a s o l u t i o n f r o m w h i c h green salts o f the f o r m M [ I r N ( S 0 ) e ( H 2 0 ) 3 ] c a n be p r e c i p i t a t e d ( 8 , J 5 ) . I t has b e e n suggested that t h e a n i o n has t h e structure s h o w n o n F i g u r e 6 w i t h a c o p l a n a r I r N u n i t a n d ττ-bonding b e t w e e n t h e 2 p o r b i t a l ( p e r p e n d i c u l a r to t h e I r N t r i a n g l e ) a n d t h e i r i d i u m atoms ( 1 3 , 19). T h e o x i d i z i n g p o w e r o f the species is consistent w i t h it's c o n t a i n i n g o n e I r ( I I I ) a n d t w o I r ( I V ) atoms p e r m o l e c u l e (8, 13). R e d u c t i o n w i t h v a n a d o u s i o n gives a s t r a w - y e l l o w species c o n t a i n i n g three I r ( I I I ) atoms p e r m o l e c u l e . X - r a y studies o n the s o m e w h a t s i m i l a r [ C r 3 0 ( C H C O O ) ( H 2 0 ) ] C l · 5 H 2 0 h a v e s h o w n that t h e C r O u n i t is p l a n a r w i t h a t r i a n g u l a r a r r a n g e m e n t of m e t a l atoms ( 9 ) . 4

3

6

4

3

4

3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

z

3

3

6

3

s

m

Figure 6. Proposed struc­ ture for indium trinuclear nitrides The Ir N unit is believed to be coplanar with the iridium atoms at the corners of an equilateral triangle. A related structure has been found for [Cr 0(Aces

3

Table VII.

Trinuclear Iridium Nitrido Complexes H

S0

2

3(NH ) [Ir Cl ] 4

3

4

> (NH )4[Ir3N(S0 )6(H 0)3]

6

4

2

4

H 0 2

[Ir N(S0 ) (H 0) ] 3

4

6

2

4

3

[Ir N(S0 ) (H 0) ] ~ 3

4

6

2

3

KOH > K [Ir N(S0 ) (OH) ] Cold 7

3

4

Caustic alkali

6

Ir N(OH)

4

3

3

u

· nH 0 2

Boiling / HC1 + C s CI Cs [Ir NCl (H 0) ] 4

3

1 2

2

3

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

64

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

O t h e r reactions of [ I r a N i S O ^ e i H k O ^ ] " are s h o w n o n T a b l e V I I . 4

Cold

c a u s t i c a l k a l i e s react to r e p l a c e

the a q u o g r o u p s ,

giving

[Ir 3

N ( S 0 ) 6 ( O H ) ] " , w h i l e h o t a l k a l i appears to r e p l a c e t h e sulfate l i g a n d s 7

3

4

to g i v e

a hydroxy

precipitate w h i c h probably

Ir N(OH)u · nH 0. 3

m a y be

described

as

T h e I r N g r o u p is s t i l l i n t a c t as r e a c t i o n w i t h s u l -

2

3

f u r i c a c i d regenerates the o r i g i n a l c o m p l e x .

The hydroxy complex

dis-

solves i n H C 1 to g i v e a species w h i c h appears to b e [ I r N C l i ( H 0 ) ] ~ . 3

2

2

3

4

W e h a v e m e a s u r e d t h e i n f r a r e d s p e c t r a of these species c o n t a i n i n g both

N and

1 4

N , a n d i n e a c h case a b a n d n e a r 780 c m " shifts d o w n w a r d

1 5

1

i n f r e q u e n c y b y some 20 c m "

1

on

to t h e a s y m m e t r i c I r N s t r e t c h . 3

1

5

N s u b s t i t u t i o n . W e assign this b a n d

T h e R a m a n s p e c t r a of the c o m p l e x e s

w e r e p o o r , o w i n g to t h e i r u n f a v o r a b l e colors, b u t w e a k b a n d s n e a r 230

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

cm"

m a y b e c a u s e d b y t h e s y m m e t r i c I r N stretch ( 5 ) .

1

3

s p l i t t i n g of the sulfate m o d e s is s i m i l a r to that o b s e r v e d ( S 0 ) ] (10), 4

S0

4

The

complex

in K i [ I r O 0

3

a n d p r e s u m a b l y arises f r o m the l o w site s y m m e t r y of the

9

groups w h i c h f u n c t i o n h e r e as b i d e n t a t e l i g a n d s .

Table VIII.

Vibrational Spectra of O x y and N i t r i d o Complexes X =

X = 0, cmr TERMINAL M-X 900-1060 300-400

VMX $mx

BRIDGING

N, cmr 1

1

950-1180 ca. 350

MmXn

Linear M - X - M V ¥

2

J

A

760-880 200-270

I

Linear VM x VM x 3

3

2

2

M - X - M - X - M

e

Triangular M v x* Mz

a

ca. 820 ca. 220

a e

3

1000-1160 260-370 ca. 1000

X 500-650 180-240

700-800 ca. 230

Comparison of the Vibrational Spectra of Oxy and Nitrido Complexes T a b l e V I I I shows the c h a r a c t e r i s t i c ranges of frequencies f o r s t r e t c h i n g a n d deformation modes for terminal a n d b r i d g i n g oxy a n d nitrido systems. I n e a c h case, t h e frequencies for the s t r e t c h i n g m o d e s are h i g h e r f o r n i t r i d e s t h a n f o r oxides. A l t h o u g h the n i t r o g e n a t o m is l i g h t e r t h a n o x y g e n , i t is l i k e l y t h a t this effect is c a u s e d i n l a r g e p a r t b y t h e f a c t t h a t

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

5. CLÉ ARE ET AL.

Nitrido Complexes

65

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch005

the nitride ligand is a more efficient ττ-donor than oxide—it is less electro­ negative and has more negative charge to impart to the metal atom (5).

Literature Cited (1) Bright, D., Ibers, J. Α., Inorg. Chem. 1969, 8, 709. (2) Chatt, J., Heaton, B. T., Chem. Commun. 1968, 274. (3) Ciechanowicz, M., Skapski, A.C.,Chem. Commun. 1969, 574. (4) Cleare, M. J., Griffith, W. P., Chem. Commun. 1968, 1302. (5) Cleare, M. J., Griffith, W. P.,J.Chem. Soc. 1970, A, 1117. (6) Clifford, A. F., Kobayashi, C. S., Inorg. Syn. 1960, 6, 204. (7) Cotton, F. Α., Lippard, S. J., Inorg. Chem. 1965, 4, 1621. (8) Delepine, M., Ann. Chim. (Paris) 1959, 1115, 1131. (9) Figgis, Β. N., Robertson, Ε. B., Nature 1965, 205, 695. (10) Griffith, W. P.,J.Chem. Soc. 1969, A, 2270. (11) Griffith, W. P.,J.Chem. Soc. 1965, 3694. (12) Jaeger, F. M., Zanstra, J. E., Proc. Acad. Sci. Amsterdam1932,35, 610 (13) Jorgensen, C. K., Acta Chem. Scand. 1959, 13, 196. (14) Jorgensen, C. K., Orgel, L. E., Mol. Phys. 1961, 4, 215. (15) Lecoq de Boisbaudran, Compt. Rend. 1883, 96, 1336, 1406, 1551. (16) Lewis, J., Wilkinson, G., J. Inorg. Nucl. Chem. 1958, 6, 12. (17) McCordie, W.C.,Watt, G. W., J. Inorg. Nucl. Chem. 1965, 27, 1130, 2013. (18) Morrow, J.C.,Acta Cryst. 1962, 15, 851. (19) Orgel, L. E., Nature 1960, 187, 505. (20) Potrafke, E. M., Watt, G. W., J. Inorg. Nucl. Chem. 1961, 17, 248. RECEIVED December 16, 1969.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6

Hydrido Group

Complexes of Platinum Metals

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

L. M. VENANZI State University of New York at Albany, Albany, Ν. Y. 12203

The preparation and properties of hydrido complexes of platinum group metals are reviewed briefly. The reactions of the more common hydrido complexes of iridium are sche matically shown. The reactions of complexes [IrHX (PhP)] (X = Cl, Br, and I), I, with the quadridentate ligand (o-Ph P · C H ) P, QP, are described and rationalized on the basis of the following reaction sequence: 2

3

3

2

6

4

3

I—HX [IrX(Ph P) ] heat [IrHX(0-C H PPh )(Ph P) ] 3

3

6

4

2

3

2

QP [IrH(0-C H PPh )(QP)]X +HX [IrHX(Ph P)(QP)]X Complexes of the latter two types have been assigned seven­ -coordinate structures on the basis of their proton and phos­ phorus-31 NMR spectra even though the oxidation number of the iridium atom is 3+. 6

4

2

3

A11 platinum group metals give hydrido complexes of general formula M H XpL (X = anionic ligand and L = uncharged ligand). Al­ though this field of chemistry is relatively new, its main development occurring over the last 10 years, the number of papers describing new compounds, their properties, and their reactions is very large and is growing at an increasing rate. Hydrido complexes also have been the subject of several reviews (9,11, 23, 24, 25,39), and the present one, like its predecessors, will be sadly out of date by the time it appears in print. As its title implies, this review restricts itself to describing and discuss­ ing compounds of platinum group metals—i.e., of ruthenium, rhodium, palladium, osmium, iridium, and platinum—although the compounds of the other transition elements and even some post-transition elements are either fully analogous or closely related to those of the platinum metals. n

m

q

66 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6.

Hydrido

V E N A N Z I

Table I.

67

Complexes

Some Better Known Types of H y d r i d o Complex of the Platinum Metals' 1

Square

Planar

[PtH L ] [Ir-HX(LL)]

trans-[MBXL ] [IrH.(LL)] [M'(LL),]X

2

2

Five-Coordinate

[IrH L ] [IrH(CO) L ]

[IrH L ]X [M'H(CO)L,] 2

3

3

Octahedral 2

!

n

2

n

2

2

2

2

2

2

[IrH L 'L ]X [IrH L'L ]X [M'H X _ L ]

2

2

2

2

[PtH X L ] [M HX (CO)L ] [M"H X . (LL) [M"HX(CO)L ] 2

2

3

m

2

3

m

3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

3

° M M L m

1

"

M ' = R h or Ir L = monodentate phosphine L L = bidentate phosphine η = 1 or 2

= P d or Pt = R u or Os = C O or monodentate phosphine = 1, 2, or 3

E v e n w i t h i n this l i m i t a t i o n , the subject is vast a n d , therefore, no a t t e m p t is m a d e to give a c o m p r e h e n s i v e d e s c r i p t i o n of the

field.

A s u r v e y of the c o m p o u n d s r e p o r t e d i n the l i t e r a t u r e shows t h a t the f o r m a t i o n of stable h y d r i d o complexes g e n e r a l l y is l i n k e d w i t h the p r e s ­ ence i n the m o l e c u l e of one or m o r e of c e r t a i n types of l i g a n d s , the m o s t frequently occurring being carbon monoxide, phosphorus ( I I I ) senic ( I I I ) d e r i v a t i v e s , a n d the c y c l o p e n t a d i e n e

and ar­

group.

I t is u s e f u l to classify the complexes b y t h e i r c o o r d i n a t i o n n u m b e r . T h e m a j o r i t y of t h e m are six-coordinate w i t h o c t a h e d r a l s t r u c t u r e , a l ­ though four- and seven-coordinate

five-coordinate

species are n u m e r o u s , a n d e v e n some

species are k n o w n .

T a b l e I shows a list of the m a i n

types of c o m p o u n d s r e p o r t e d i n the l i t e r a t u r e . P r e p a r a t i v e m e t h o d s for h y d r i d o complexes

vary widely.

Some

the m o r e f r e q u e n t l y u s e d of t h e m a r e : (1)

A c t i o n of c o m p l e x h y d r i d e s ,

e.g., LiAlH

4

as-[RuCl (Me PCH CH PMe ) ] 2

2

2

2

2

>

2

imns-[RuHCl(Me PCH CH PMe ),] 2

(2)

2

2

2

A c t i o n of alcohols i n the presence of a base,

(16)

e.g.,

Ph P 3

(NH ) [OsBr ]< 4

2

6

• [ O s H B r ( C O ) ( P h P ) ] (41) MeOCH CH OH 3

2

(3)

P r o t o n a t i o n of complexes,

3

2

e.g., H+

[Ru (x-C H ) (CO) ] 2

5

5

2

6

> [Ru H(x-C H ) (CO) ]+ 2

5

5

2

6

(20)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

of

68 (4)

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

A c t i o n of h y d r a z i n e , e.g., N H 2

· H 0 > i r a r c s - [ P t H C l ( E t P ) ] (17)

4

2

cie-[PrCl,(Et«P)J

3

2

H y d r i d o complexes are also f o r m e d i n some u n u s u a l r e a c t i o n s : MeOCH CH OH > [ P h A s ] [ P d H C l ( C O ) ] (27) at r o o m t e m p . 2

(1) P d C l + C O + [ P h A s ] C l 2

4

2

4

H 0 > [PtHI (Pr P) ]

2

2

(2) [ P t I ( M g I ) ( P r P ) ] 3

2

3

(19)

2

Some of the p r e p a r a t i v e m e t h o d s are best d e s c r i b e d , at least f o r m a l l y , as i n v o l v i n g a n " o x i d a t i v e a d d i t i o n " of a m o l e c u l e to a c o m p l e x of a m e t a l Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

i o n or a t o m i n a l o w o x i d a t i o n state. E x a m p l e s of this t y p e of r e a c t i o n are shown below. (1)

A d d i t i o n of m o l e c u l a r h y d r o g e n , H

[Rh(Me PCH CH PMe ) ]Cl 2

(2)

2

2

2

e.g.,

2

•aV[RhH (Me PCH CH PMe ) ]Cl

2

2

A d d i t i o n of h y d r o g e n h a l i d e ,

2

2

2

2

2

(12)

e.g.,

HC1 [Rh(Ph PCH CH PPh ) ]Cl 2

(3)

2

2

2

• a s - [ R h H C l ( P h P C H C H P P h ) ] C l (38)

2

2

A d d i t i o n of other h y d r i d e s ,

2

2

2

2

e.g.,

H S [Pt(Ph P) ] — U 3

* m n s - [ P t H ( S H ) ( P h P ) ] (35)

3

3

2

A p a r t i c u l a r l y i n t e r e s t i n g t y p e of o x i d a t i v e a d d i t i o n r e a c t i o n is the " h y d r o g e n a b s t r a c t i o n " r e a c t i o n , some examples of w h i c h are g i v e n b e l o w . (1) [ R u ( M e P C H C H P M e ) ] <=> [ R u H ( C H P ( M e ) C H C H P M e ) 2

2

2

2

2

2

(Me PCH CH PMe )] 2

2

2

2

2

2

2

(U)

heat (2) [ I r C l ( P h P ) ] 3

• [ I r H C l ( o - C H P P h ) ( P h P ) ] (7)

3

6

(3) i m n s - [ P t C l ( E t P ) ] + L i C B 2

3

2

1 0

H

1 0

4

2

3

2

C M e -> [ P t ( C B H C M e ) 1 0

1 0

( C H C H P E t ) ( E t P ) ] (8) 2

2

2

3

T h e s e reactions are of p a r t i c u l a r interest as t h e y c o u l d p r o v i d e the basis f o r a n u m b e r of c a t a l y t i c processes i n v o l v i n g s a t u r a t e d h y d r o carbons. T h e p r o p e r t i e s of h y d r i d o complexes v a r y w i d e l y , r a n g i n g f r o m those w h i c h c a n b e d e t e c t e d o n l y s p e c t r o s c o p i c a l l y to those that s h o w r e m a r k a b l e g e n e r a l c h e m i c a l s t a b i l i t y . S t a b i l i t y g e n e r a l l y tends to b e at a m a x i m u m i n c o m p o u n d s of the t h i r d t r a n s i t i o n series. F u r t h e r m o r e , f o r a g i v e n m e t a l a n d t y p e of c o m p l e x , s t a b i l i t y appears to b e at its h i g h e s t w h e n

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6.

Hydrido

V E N A N Z I

69

Complexes

p h o s p h i n e l i g a n d s are present i n the m o l e c u l e .

Naturally, it w o u l d

be

f o o l h a r d y to take the a b o v e k i n d of s t a b i l i t y as a g u i d e to t h e r m o d y n a m i c s t a b i l i t y of the m e t a l - h y d r o g e n b o n d , as one w o u l d d r a w a c o r r e l a t i o n b e t w e e n a s t a b i l i t y w h i c h is a c o m p o s i t e of a n u m b e r of t h e r m o d y n a m i c a n d k i n e t i c factors a n d a r e l a t i v e l y s m a l l energy t e r m s u c h as the M - H b o n d energy. I t is regrettable that t h e r m o d y n a m i c d a t a o n h y d r i d o c o m ­ plexes are t o t a l l y l a c k i n g b u t t h e y are almost i m p o s s i b l e to o b t a i n . T h e most c o m m o n l y

quoted physical data on hydrido

are the v i b r a t i o n a l spectra a n d p r o t o n m a g n e t i c resonance

complexes parameters.

H y d r i d o complexes e x h i b i t M - H s t r e t c h i n g v i b r a t i o n s i n the r e g i o n 1 7 0 0 2250 c m

- 1

a n d M - H b e n d i n g m o d e s i n the r e g i o n 6 6 0 - 8 5 0

cm . - 1

The

absence of a b s o r p t i o n i n the a b o v e regions, h o w e v e r , is not to b e t a k e n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

as a n i n d i c a t i o n t h a t the m o l e c u l e u n d e r e x a m i n a t i o n does not c o n t a i n M - H bonds.

S e v e r a l h y d r i d o complexes are k n o w n w h e r e M - H b o n d s

w e r e not detectable b y i n f r a r e d spectroscopy

(28, 34, 37).

Proton mag­

n e t i c resonance, o n the other h a n d , is a m o r e g e n e r a l l y u s e f u l t e c h n i q u e . P r o t o n resonances i n h y d r i d o complexes h a v e v e r y c h a r a c t e r i s t i c τ-values r a n g i n g f r o m 11 to 42 p p m r e l a t i v e to T M S . T h e l i m i t a t i o n here is i n t r o ­ d u c e d b y s o l u b i l i t y a n d b y fast exchange p h e n o m e n a a l t h o u g h , i n m a n y cases, the f o r m e r difficulty c a n be o v e r c o m e b y s p e c t r u m a c c u m u l a t i o n a n d the latter b y l o w e r i n g the s a m p l e t e m p e r a t u r e . H y d r i d o l i g a n d s e x h i b i t a v e r y strong trans effect w h i c h appears to operate m a i n l y b y a l a b i l i z a t i o n of the b o n d i n trans p o s i t i o n to the M - H b o n d . T h i s l a b i l i z a t i o n g e n e r a l l y is associated w i t h a l e n g t h e n i n g of the b o n d w h i c h has b e e n l a b i l i z e d , a n effect o p e r a t i n g m a i n l y b y trans i n ­ fluence

(36)

c a u s e d b y a selective r e h y b r i d i z a t i o n of the m e t a l σ orbitals

l e a d i n g to the M - H b o n d h a v i n g a large d a n d s c o m p o n e n t .

S u c h effects

are most e v i d e n t i n square p l a n a r complexes, b u t t h e y also h a v e observed i n octahedral

been

complexes.

T h e g e n e r a l r e a c t i v i t y of h y d r i d o complexes is h i g h , a n d i t is r e l a t e d m a i n l y to the c o o r d i n a t i o n n u m b e r of the c e n t r a l m e t a l a t o m . four- a n d

five-coordinate

six-coordinate species.

Thus,

complexes u s u a l l y are m o r e r e a c t i v e t h a n r e l a t e d T h e latter, h o w e v e r , o r d i n a r i l y are m o r e r e a c t i v e

t h a n the c o r r e s p o n d i n g complexes

w h i c h d o not c o n t a i n M - H b o n d s .

S u c h r e a c t i v i t y m a y b e i n d u c e d either b y o p e r a t i o n of the trans effect or, w h e r e possible, b y the r e d u c t i v e e l i m i n a t i o n of a m o l e c u l e of h y d r o g e n h a l i d e w i t h or w i t h o u t assistance of a base. T h e c h e m i c a l b e h a v i o r of M - H b o n d s varies f r o m t h a t of a n a c t i v e h y d r i d e to that of a strong a c i d . T h i s w i d e v a r i a t i o n i n p r o p e r t i e s , h o w ­ ever, m a y be a c h i e v e d w i t h a r e l a t i v e l y s m a l l v a r i a t i o n of c h a r g e d i s t r i b u ­ t i o n (4).

A t t e m p t s to correlate c h e m i c a l shifts a n d c o u p l i n g constants

w i t h b o n d distances a n d electron d i s t r i b u t i o n i n M - H b o n d s h a v e l e d

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

70

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

t o t h e c o n c l u s i o n that s u c h correlations m a y b e v a l i d o n l y w h e n v e r y s m a l l changes are m a d e to the l i g a n d s

(3).

T h e f e v e r i s h interest i n h y d r i d o complexes

has, as its m a i n cause,

the t r e m e n d o u s p o t e n t i a l of these reactions i n c a t a l y t i c systems.

In a

r e l a t i v e l y short s p a n of t i m e , h y d r i d o complexes h a v e b e e n f o u n d to p l a y a r o l e i n a significant n u m b e r of c a t a l y t i c processes ( 6 , 9)—e.g., o l i g o m e r i z a t i o n of olefins ( r h o d i u m ) , d e c a r b o x y l a t i o n reactions

(rhodium),

a n d hydrogénation reactions ( r u t h e n i u m , o s m i u m , r h o d i u m , i r i d i u m , a n d p l a t i n u m ) . D i s c u s s i o n of these a p p l i c a t i o n s w o u l d go b e y o n d the scope of the present treatment. T h e r e m a i n d e r of this r e v i e w is d e v o t e d to g i v i n g a closer l o o k at the h y d r i d o complexes of i r i d i u m a n d t h e i r reactions. I r i d i u m gives the Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

most extensive a n d versatile range of h y d r i d o complexes of a n y p l a t i n u m metal (29).

T h e m a i n types of c o m p o u n d s

k n o w n a n d some of t h e i r

reactions are s h o w n i n T a b l e I I . T o this, one m u s t a d d the

hydrogen

a b s t r a c t i o n r e a c t i o n m e n t i o n e d earlier. T h e w i d e r a n g e of h y d r i d o complexes f o r m e d b y i r i d i u m is a c l e a r i n d i c a t i o n t h a t this m e t a l has a p a r t i c u l a r l y strong t e n d e n c y to f o r m I r - H bonds.

T h e reason for this affinity is n o t a p p a r e n t as yet, b u t this c o n -

c l u s i o n is r e i n f o r c e d constantly b y n e w d a t a . T h u s , one c a n isolate stable seven-coordinate

complexes

of i r i d i u m ( I I I ) .

T h e quadridentate ligand

( o - P h P · C H ) P , Q P , reacts w i t h [ I r H X ( P h P ) ] ( X = 2

6

4

3

2

3

CI, Br, and

8

I ) i n r e f l u x i n g c h l o r o b e n z e n e to give [ I r H X ( P h P ) ( Q P ) ] X , I , w h i c h is 3

a seven-coordinate h y d r i d o c o m p l e x of i r i d i u m ( I I I ) .

(21)

The infrared

s p e c t r u m does n o t s h o w a n I r - H s t r e t c h i n g v i b r a t i o n , b u t t h e presence of a h y d r i d o l i g a n d is c l e a r l y v i s i b l e i n the p r o t o n m a g n e t i c

resonance

spectrum. T h e f o r m a t i o n of these c o m p o u n d s is p r e c e d e d b y that of a species of c o m p o s i t i o n

[ I r ( P h P ) ( Q P ) ] X , I I , w h i c h reacts w i t h N a [ B P h ] 3

to

4

g i v e the same c o m p l e x i r r e s p e c t i v e of the n a t u r e of the a n i o n X i n the s t a r t i n g m a t e r i a l , [ I r H X ( P h P ) ] . T h e i r N M R s p e c t r a (22) 2

3

[IrHX(Ph P)(QP)]X. 3

indicate

3

the presence of I r - H b o n d s a n d t h e i r r e a c t i o n w i t h H X gives

compounds

C o m p l e x e s I I are, therefore, t e n t a t i v e l y f o r m u -

l a t e d as [ I r H ( o - C H P P h ) ( Q P ) ] X . 6

4

2

I n a n a t t e m p t to g a i n a better u n d e r s t a n d i n g of the factors c a u s i n g t h e f o r m a t i o n of the a b o v e seven-coordinate h y d r i d o complexes, the r e a c t i o n of [ I r H C l ( P h P ) ] w i t h r e f l u x i n g c h l o r o b e n z e n e 2

3

3

was e x a m i n e d .

P r e l i m i n a r y experiments suggest that the p r i m a r y step is t h e e v o l u t i o n of

hydrogen

chloride

and

formation

of

the

unstable

intermediate

[ I r C l ( P h P ) ] , w h i c h reacts f u r t h e r to g i v e a n u m b e r of p r o d u c t s . 3

3

has the c o m p o s i t i o n I r C l ( P h P )

3

III,

compound

3

of

Bennett

and

Milners

One

a n d is l i k e l y to b e a n i s o m e r i c f o r m , (7),

[IrHCl(o-C H PPh )6

4

2

( P h P ) ] . T h e others, s o m e p u r e l y o r g a n i c a n d some i r i d i u m - c o n t a i n i n g , 3

2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

6.

Hydrido

V E N A N Z I

Table II.

Y

Some Iridium H y d r i d o Complexes and T h e i r Reactions

2

3

(44)

HX

->

[IrH L ](C10<)

-[IrHX L ] 2

71

Complexes

(1)

HCIO4

3

KOH

(30)

H X (2) [IrH XL ] 2

* 3

4

K O H (2)

vie- and. raer-[IrH L ] (31)

3

[IrH,L ](C10«)

{2,10)

3

(82)

[IrH L ]

<

3

2

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

LiBH

(14)

4

[IrHCl(SnCI )(CO)L ] 3

2

NaBH

4

wc-[IrH (CO)L ] 3

2

« MeOCH CH OH/KOH < > MeOCH CH OH/H 0/L s

2

2

2

2

are s t i l l u n d e r i n v e s t i g a t i o n (33).

T h u s , one c a n p r e s u m e t h a t c o m p o u n d

I I I reacts w i t h the l i g a n d Q P to g i v e c o m p o u n d s

of t y p e I , a c c o u n t i n g

f o r the r e t e n t i o n of the elements of one m o l e c u l e of t r i p h e n y l p h o s p h i n e i n compounds

I. T h e interest i n complexes

I arises f r o m the f a c t t h a t

t h e y e x h i b i t c o o r d i n a t i o n n u m b e r seven despite the d e l e c t r o n c o n f i g u r a 6

t i o n of the m e t a l i o n . T h e f o r m a t i o n of s u c h s e v e n - c o o r d i n a t e

species

m a y b e assisted b y the fact t h a t t h e seventh l i g a n d is a h y d r o g e n a t o m , b u t t h e significance of t h e i r i s o l a t i o n is that i t is reasonable to p o s t u l a t e , w h e n necessary, the f o r m a t i o n of a seven-coordinate t r a n s i t i o n state i n t e r -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

72

PLATINUM GROUP METALS AND COMPOUNDS

mediate even when the formal electron configuration of the metal atom is d . The formation of such a range of hydridic compounds by iridium and the paucity of catalytic processes based on complexes of this element may be linked to the greater inertness of compounds of elements of the third transition series relative to the corresponding species with metals of the second transition series. However, iridium chemistry may provide a very fertilefieldfor the study of homogeneous catalysis. The key to success in this direction may lie in the use of complexes which are coordinatively unsaturated and contain a strong labilizing group (6, 9). Thus, [IrHCl (Ph P) ] in chlorobenzene solution reacts with dimethyl­ formamide ^t 13jS° with formation of [IrCl(CO) (Ph P) ], IV, which is in equilibrium wifh [IrHCl (CO) (Ph P) ]. Compound IV catalytically decomposes dimethylformamide into carbon monoxide and dimethylamine, but the decomposition rate is proportional to the concentration of IV and amide, indicating that the rate-determining step is the formation of the adduct between IV and dimethylformamide and not the decom­ position of the adduct which regenerates IV. When [IrHCI (Ph P) ] reacts with dimethylacetamide, however, only a stoichiometric reaction, which is still under investigation, is observed (33). This review has been necessarily brief, but I hope sufficient to show that thefieldof platinum metal hydrides is one of unlimited potential for both the academic and industrial chemist. G

2

3

3

3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

2

3

2

2

2

3

3

Literature Cited (1) Angoletta, M., Gazz. Chim. Ital. 1962, 92, 811. (2) Angoletta, M., Araneo, Α., Gazz. Chim. Ital. 1963, 93, 1343. (3) Atkins, P. W., Green, J. C., Green, M. L. H., J. Chem. Soc. 1968, (A), 2275. (4) Basch, H., Ginsburg, A. P.,J.Phys. Chem. 1968, 73, 854. (5) Bath, S. S., Vaska, L., J. Am. Chem. Soc. 1963, 85, 3500. (6) Bird, C. W., "Transition Metal Intermediates in Organic Synthesis," Logos Press and Academic Press, London, 1967. (7) Bennett, M. J., Milner, D. L.,J.Am. Chem. Soc. 1969, 91, 6983. (8) Bresadola, S., Rigo, P., Turco, Α., Chem. Commun. 1968, 1205. (9) Candin, J. P., Taylor, Κ. Α., Thompson, D. T., "Reactions of Transition Metal Complexes," Elsevier, Amsterdam, 1968. (10) Canziani, F., Zingales, F., Rend.Ist.Lombardo Sci., A. 1962, 96, 513. (11) Chatt, J., Science 1968, 160, 3829. (12) Chatt, J., Butter, S. Α., Chem. Commun. 1967, 501. (13) Chatt, J., Coffey, R. S., Shaw, B. L.,J.Chem. Soc. 1965, 7391. (14) Chatt, J., Davidson, J. M.,J.Chem. Soc. 1965, 843. (15) Chatt, J., Field, A. E., Shaw, B. L., J. Chem. Soc. 1961, 290. (16) Chatt, J., Hayter, R. G.,J.Chem. Soc. 1961, 2605. (17) Chatt, J., Shaw, B. L.,J.Chem. Soc. 1962, 5075. (18) Craig Taylor, R., Young, J. F., Wilkinson, G., Inorg. Chem. 1966, 5, 20. (19) Cross, R. J., Glockling, F.,J.Chem. Soc. 1965, 5422.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch006

6.

VENANZI

Hydrido Complexes

73

(20) Davison, Α., McFarlane, W., Pratt, L., Wilkinson, G., J. Chem. Soc. 1962, 3653. (21) Dawson, J. W., Kerfoot, D. G. E., Preti, C., Venanzi, L. M., Chem. Com­ mun. 1968, 1689. (22) Dawson, J. W., Venanzi, L. M., unpublished observations. (23) Ginsberg, A. P., Transition Metal Chem. 1965, 1, 111. (24) Green, M. L. H., Jones, D. J., Advan. Inorg. Chem. Radiochem.1965,7, 115. (25) Griffith, W. P., "The Chemistry of the Rarer Platinum Metals," Inter­ science, London, 1967. (26) Hayter, R. G.,J.Am. Chem. Soc. 1961, 83, 1259. (27) Kingston, J. V., Scollary, G. R., Chem. Commun. 1969, 455. (28) Levison, J. J., Robinson, S. D., Chem. Commun. 1968, 1405. (29) Malatesta, L., Helv. Chim. Acta, Fasciculus Extraordinarius Alfred Werner, 1967, 147. (30) Malatesta, L., "Symposium on Current Trends in Organometallic Chem­ istry," (Abstracts), Cincinnati, June 12-15, 1963, p. 71A. (31) Malatesta, L., Angoletta, M., Araneo, Α., Canziam, F., Angew. Chem. 1961, 73, 273. (32) Malatesta, L., Caglio, G., Angoletta, M., J. Chem. Soc. 1965, 6974. (33) Martelli, M., Venanzi, L. M., unpublished observations. (34) Misono, Α., Uchida, Y., Hidai, M., Araki, M., Chem. Commun. 1968, 1044. (35) Morelli, D., Segre, Α., Ugo, R., LaMonica, G., Cenini, S., Conti, F., Bonati, F., Chem. Commun. 1967, 524. (36) Pidcock, Α., Richards, R. D., Venanzi, L. M., J. Chem. Soc., A 1966, 1707. (37) Sacco, Α., Rossi, M., Inorg. Chim. Acta 1968, 2, 127. (38) Sacco, Α., Ugo, R.,J.Chem. Soc. 1964, 3274. (39) Shaw, B. L., "Inorganic Hydrides," Pergamon, Oxford, 1967. (40) Shaw, B. L., Chatt, J., Proc. Intern. Congr. Coordination Chem., 7th Stockholm, 1962, Abstracts, p. 293. (41) Vaska, L., DiLuzio, J. W., J. Am. Chem. Soc. 1961, 83, 1262. (42) Vaska, L., DiLuzio, J. W., Ibid., 1961, 83, 2784. (43) Vaska, L., DiLuzio, J. W., Ibid., 1962, 84, 679. (44) Vaska, L., DiLuzio, J. W., Ibid., 1962, 84, 4989. (45) Vaska, L., Rhodes, L. E.,J.Am. Chem. Soc. 1965, 87, 4970. RECEIVED January 28, 1970.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7

Ultraviolet Spectroscopic Qualities of Platinum G r o u p Compounds

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

DON S. MARTIN, JR. Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa 50010

Coordination compounds of the platinum group elements have excited states which provide spectral absorptions in the ultraviolet region, extending through the visible into the near IR, which must be classified together from their similarity in origin. Many of the transitions are obscured by the broad bands from their more intense neighboring transitions, so only a few can be identified for a single complex Several analytical and kinetics applications are discussed. In addition, applications of polarized crystal spectra, absorption inlow-temperatureorganic glasses, and the use of magnetic circular dichroism which can be combined with molecular orbital treatments, spin-orbit coupling, vibronic excitation, and metal—metal interactions are described fo the identification of transitions in specific instances. *Tphe bright colors of the coordination complexes of transition metal elements, including the platinum group metals, were of great assistance to pioneer workers with these materials. Thus, chemical changes could be followed visually; it was frequently very easy from their colors to demonstrate the existence of isomers upon which Alfred Werner was able to base his monumental theory of coordination. Such early studies were limited to a simple qualitative visual evaluation of the color. By the mid-twentieth century, dependable spectrophotometers became commercially available and very quickly were recognized as essential laboratory tools for the characterization of the coordination complexes. These new instruments permitted quantitative evaluation of the absorption of light; procurement of the instruments was usually justified by the convenience, versatility, and speed which they introduced into the quantitative analysis and identification of these materials. 74

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

M A R T I N

Ultraviolet

Spectrophotometry

Spectroscopic

75

Qualities

is t o d a y , w i t h o u t q u e s t i o n , the most w i d e l y

used

i n s t r u m e n t a l t e c h n i q u e f o r kinetics studies, w h i c h r e q u i r e the q u a n t i t a ­ t i v e c h a r a c t e r i z a t i o n of c h a n g i n g systems. M o d e r n instruments have extended

the s p e c t r a l r a n g e

from

the

severely l i m i t e d v i s u a l r e g i o n i n t o b o t h the near i n f r a r e d a n d the u l t r a ­ v i o l e t r e g i o n . A r e g i o n e x t e n d i n g f r o m 1200 d o w n to 200 τημ is r i c h w i t h the e l e c t r o n i c spectra i n v o l v i n g the d-orbitals of t r a n s i t i o n m e t a l c o m ­ pounds.

Since strict adherence

to the u l t r a v i o l e t r e g i o n w o u l d b e

i n c o m p l e t e , c o n s i d e r a t i o n here w i l l b e d i r e c t e d to t h e b r o a d e r of the accessible e l e c t r o n i c spectra for t h e p l a t i n u m m e t a l

so

region

complexes.

T h e l i t e r a t u r e contains l i t e r a l l y h u n d r e d s of a b s o r p t i o n spectra for t h e c o o r d i n a t i o n complexes of the p l a t i n u m elements,

spectra

which

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

d e p e n d u p o n the n a t u r e of the v a r i o u s l i g a n d s , the o x i d a t i o n state, a n d the electronic configuration. I n the present r e v i e w , a c o m p l e t e c a t a l o g i n g of a l l of these spectra w i l l not b e a t t e m p t e d .

R a t h e r , attention w i l l

be

l i m i t e d to a f e w complexes f o r w h i c h the l i g a n d s are r e l a t i v e l y s i m p l e groups, s u c h as h a l i d e s , a m m o n i a , w a t e r , or s i m p l e amines w h i c h b y themselves d o not possess a h i g h a b s o r p t i o n i n the s p e c t r a l r e g i o n of interest. means

T y p i c a l illustrations of the a n a l y t i c a l possibilities as w e l l as of

chemical characterization w i t h

the systems

are

presented.

H o w e v e r , the a n a l y t i c a l u t i l i t y of the spectra, a l t h o u g h q u i t e i m p r e s s i v e , has b e e n o v e r s h a d o w e d

w i t h i n the past 15 years b y the a p p l i c a t i o n of

c r y s t a l or l i g a n d field theory, a n d s u b s e q u e n t l y b y m o l e c u l a r o r b i t a l treatments, w h i c h h a v e

provided

a n u n d e r s t a n d i n g of

the

observed

a b s o r p t i o n b a n d s a n d t h e i r assignment to p r e d i c t a b l e e l e c t r o n i c t r a n s i ­ tions.

T h e development

of these theories has b e e n one

of t h e

most

e x c i t i n g events i n m o d e r n i n o r g a n i c c h e m i s t r y , for t h e y h a v e p r o v i d e d a means of i d e n t i f y i n g the e l e c t r o n i c states a n d testing v a r i o u s concepts a n d t h e o r e t i c a l calculations of b o n d i n g . O n e of the v e r y active regions of r e s e a r c h i n recent years has i n ­ v o l v e d attempts to e x t e n d e x p e r i m e n t a l m e t h o d s to p r o v i d e a d d i t i o n a l s p e c t r a l i n f o r m a t i o n f o r m o r e definitive e l e c t r o n i c state assignments.

Spectra of Hexahalo-Complexes in Aqueous Solutions The

p l a t i n u m metals

hexahalo-complexes.

i n the heavy

series

form

especially

inert

S p e c t r a for a n u m b e r of these w e r e r e p o r t e d

by

Jorgensen ( 1 4 , 1 5 , 1 6 ) . A f e w of these w h i c h are i l l u s t r a t i v e of the effects of v a r i o u s ligands a n d of the e l e c t r o n i c configurations h a v e b e e n r e p r o ­ d u c e d i n F i g u r e 1. U s u a l l y , the solutions f r o m w h i c h these spectra w e r e o b t a i n e d h a v e c o n t a i n e d excess h a l i d e i o n to r e d u c e a n y s o l v a t i o n effect. A n u m b e r of l i m i t a t i o n s f o r the a n a l y t i c a l a n d s t r u c t u r a l u t i l i t y of the spectra are i m m e d i a t e l y e v i d e n t f r o m the spectra i n F i g u r e 1.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

F i r s t of

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

76

P L A T I N U M

Figure

1.

G R O U P

M E T A L S

A N D

Electronic absorption spectra for some halide of the heavy platinum group elements

complexes

a l l , the spectra consist of a l i m i t e d n u m b e r of v e r y b r o a d bands.

C O M P O U N D S

absorption

I t is n o t possible to d e t e r m i n e f r o m the s p e c t r u m of a m i x t u r e

of s e v e r a l complexes the c o m p o s i t i o n of the m i x t u r e , or f r e q u e n t l y even to i d e n t i f y the

components.

N e v e r t h e l e s s , s o m e conclusions

of

con­

s i d e r a b l e v a l u e are possible. For PtCl -, 6

cm"

2

the m o l a r a b s o r p t i v i t y at 38,000

cm"

1

is

>

20,000

M ' . F o r a p u r e s o l u t i o n , a 10-cm c e l l w i l l y i e l d a n absorbance

1

1

of

0.1 f o r a 0.5 μΜ s o l u t i o n . H i g h sensitivity i n analysis is therefore p o s ­ sible, p r o v i d e d

interferences

P t C U " at 30,000 c m 2

P t B r ~ is 10,000 c m " 6

2

are absent.

is 600 c m

1

1

- 1

The

m o l a r a b s o r p t i v i t y for

M " , whereas t h e m o l a r a b s o r p t i v i t y for 1

M " . It is possible f r o m the spectra, therefore, to 1

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

Ultraviolet

M A R T I N

Spectroscopic

77

Qualities

p l a c e a f a i r l y s m a l l l i m i t u p o n the c o n t a m i n a t i o n b y the P t B r ' w h i c h 2

6

m a y b e present. W h e r e a s the h e i g h t of a s p e c t r a l p e a k is a g o o d measure for the c o n c e n t r a t i o n of the p r e d o m i n a n t species, the a b s o r b a n c e

at a

s p e c t r a l v a l l e y is v e r y sensitive to the presence of i m p u r i t i e s . F o r s y n ­ thetic p r e p a r a t i o n s , one of the most r e l i a b l e c r i t e r i a of p u r i t y is the peak-to-valley ratio i n an absorption spectrum. A very valuable prepara­ tive technique involves continued fractional recrystallization u n t i l such a p e a k - t o - v a l l e y r a t i o does n o t increase u p o n e a c h s u b s e q u e n t tallization.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

°h

D

4

h

. .η*<σ-) / — e * (σ) α

,

α *

;

I g

19

if

Ι

6s /

6s

b,J(x -y ) 2

/ KJ 5d

2

b (xy) 2g

/ —iU„

«

2g

w

H

ig Γ 'eg"(«,yz)

//,''

α

22—>k-

(ζ ) 2

7Γ

7Γ

t . — ' / _2L

b

u

/ /

/

2 u

°2u

_2L /"

/ Metal

MO

Ligand

Metal

MO

Ligand

Figure 2. Correlation diagram for molecular orbitals in co­ ordination complexes with O symmmetry and with D sym­ metry. Only the principal correlation lines are shown and the g states arising from the ligand σ and π orbitah are omitted for simplicity h

A h

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

recrys­

78

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

O n l y a h a n d f u l of b r o a d e l e c t r o n i c t r a n s i t i o n b a n d s , s e v e r a l t h o u s a n d w a v e n u m b e r s i n w i d t h , c a n b e i d e n t i f i e d f r o m the s p e c t r u m of a n y one c o m p l e x . F r e q u e n t l y , n o t m o r e t h a n six s u c h b a n d s are r e s o l v a b l e . gensen has p r o v i d e d i n t e r p r e t a t i o n s of these s p e c t r a a c c o u n t for m a n y of t h e i r o b s e r v e d

features.

(17,

A 1-electron

Jor­

which

18)

molecular

o r b i t a l c o r r e l a t i o n d i a g r a m f o r the O s y m m e t r y g r o u p , w h i c h a p p l i e s h

to these systems, has b e e n i n c l u d e d i n F i g u r e 2.

A sigma orbital from

e a c h of the six l i g a n d s interacts w i t h the s, the p, a n d the d-(e )

orbitals

g

to p r o v i d e six s i g m a b o n d i n g orbitals. O n l y the t h r e e a s y m m e t r i c t

orbi­

lu

tals of this set are i n d i c a t e d i n F i g u r e 2. T h e t w o π orbitals of e a c h l i g a n d g e n e r a l l y are n o t c o n s i d e r e d to p r o v i d e a strong c o n t r i b u t i o n to

the

b o n d i n g f o r h a l i d e s . T w o sets of t h r e e - f o l d degenerate o r b i t a l s , the t

lu

a n d the t , are s h o w n .

T h e levels for the s y m m e t r i c ( g )

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

2u

sigma and π

orbitals h a v e b e e n o m i t t e d f o r s i m p l i c i t y . A set of s y m m e t r i c o r b i t a l s , t h e t

2g

c o m p r i s i n g p r i n c i p a l l y the m e t a l

d-orbitals, are next i n e n e r g y a n d a b o v e t h e m , s e p a r a t e d b y the f a m i l i a r Δ

0

o r 10 Dq,

are the a n t i b o n d i n g e * g

the a n t i b o n d i n g t * a n d the a * lu

lg

p a i r . A t m u c h h i g h e r energies are

orbitals. S i n c e f o r the h e a v y series of

p l a t i n u m metals Δ is of the o r d e r of 30,000 c m " , the complexes are of the 1

0

spin-paired a n d inert type.

U p to six electrons c a n b e i n the t

2g

orbitals, a n d a l l orbitals b e l o w these are filled as w e l l i n the A t r a n s i t i o n of a n e l e c t r o n f r o m the filled o r b i t a l s , t

lu

e i t h e r the t

2g

( π ) or t

2u

or the e * o r b i t a l w i l l b e d i p o l e - a l l o w e d . g

set of

complexes. ( i r ) , to

Since i n these

transitions the electron moves p r i m a r i l y f r o m a n o r b i t a l o n the l i g a n d to one o n the m e t a l , s u c h a t r a n s i t i o n is u s u a l l y d e s i g n a t e d as a L -> M c h a r g e transfer. S u c h transitions are expected to l e a d to b a n d s w i t h the m o l a r a b s o r p t i v i t y ,C.,at the p e a k greater t h a n 1000 c m " M " . T r a n s i t i o n s 1

of electrons f r o m t

2g

1

to t * w o u l d b e a l l o w e d b y s y m m e t r y , a n d the lu

p o s s i b i l i t y of t h e i r presence i n the spectra m u s t b e c o n s i d e r e d as w e l l . H o w e v e r , i n most instances t h e y are b e l i e v e d to o c c u r at h i g h e r energy, f r e q u e n t l y b e y o n d the r a n g e of observations w i t h h a l i d e s . T r a n s i t i o n s of a n e l e c t r o n f r o m a t

2g

bidden.

o r b i t a l to e * are d i p o l e - f o r g

B a n d s w i t h a m o l a r a b s o r p t i v i t y of the order of 100 c m " M " 1

1

u s u a l l y are assigned to s u c h d-d transitions i n w h i c h the spins are u n ­ changed—i.e.,

t h e y are s p i n - a l l o w e d .

Since the h e a v y metals h a v e a

h i g h s p i n - o r b i t c o u p l i n g , a n d the s p i n is n o l o n g e r a g o o d q u a n t u m n u m ­ b e r b y the m i x i n g of different m u l t i p l e t states, b a n d s are

observable

b e t w e e n states w h i c h h a v e m a j o r components w i t h different s p i n m u l t i ­ plicities.

T h e s e are d e s i g n a t e d as the s p i n - f o r b i d d e n b a n d s .

the m i x i n g of states is sufficiently great that there m a y b e

Indeed,

considerable

a m b i g u i t y i n the assignment of transitions. T h e s i t u a t i o n is t r e a t e d b y c o n s i d e r i n g the d o u b l e

r o t a t i o n a l groups

o r b i t a l a n d s p i n w a v e functions.

w h i c h encompass

both

the

F o r e x a m p l e , the electron s p i n f u n c -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

M A R T I N

Ultraviolet

Spectroscopic

79

Qualities

tions, + 1 / 2 , — 1 / 2 , are b a s i c f u n c t i o n s f o r t h e y*(e ) 2

irreducible repre­

sentation f o r the O ' g r o u p . S i n g l e t a n d t r i p l e t f u n c t i o n s h a v e γ ι ( α ι ) a n d 7 (*i)

symmetry, respectively.

4

T h e a c t u a l states m a y b e f o r m e d

from

a l i n e a r c o m b i n a t i o n o f w a v e functions w i t h different m u l t i p l i c i t i e s . T h e c o n t r i b u t i o n o f m i n o r m u l t i p l i c i t i e s m a y b e sufficiently great t h a t " s p i n a l l o w e d " transitions h a v e a n e n h a n c e m e n t f a c t o r o f o n l y 4 t o 10 over " s p i n - f o r b i d d e n " transitions.

A s the wavelength

decreases,

q u e n t l y possible to observe i n a s p e c t r u m first s o m e symmetry-forbidden

i t is f r e ­

spin-forbidden,

transitions, t h e n t h e s p i n - a l l o w e d b u t s y m m e t r y -

f o r b i d d e n , a n d finally some c h a r g e transfer b a n d s .

However, only a

f r a c t i o n o f the possible transitions are observable, a n d m a n y are " h i d d e n " u n d e r t h e b r o a d peaks o f m o r e intense transitions i n s o l u t i o n spectra o f Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

the t y p e i l l u s t r a t e d i n F i g u r e 1. T h e o r y has n o t y e t r e a c h e d a stage w h e r e energies o r e v e n t h e o r d e r i n g o f states c a n b e c a l c u l a t e d r e l i a b l y f o r t r a n s i t i o n e l e m e n t plexes.

Therefore,

complementary

com­

contributions a n d cooperation b e ­

tween experiment a n d theory are needed i n the unravelling of energy states a n d t h e d e s c r i p t i o n o f b o n d i n g f o r these i m p o r t a n t systems. T h e ^ - c o n f i g u r a t i o n , w h i c h occurs for t h e m u l t i t u d e o f i n e r t C o ( I I I ) complexes, is i l l u s t r a t e d b y the complexes o f I r ( I I I ) a n d the P t ( I V ) c o m ­ plexes i n F i g u r e 1. T h e g r o u n d state c o n f i g u r a t i o n is p r i m a r i l y t

G

S i n c e the t

2g

—

o r b i t a l s a r e filled, there is n o p o s s i b i l i t y o f a t r a n s i t i o n

2g

f r o m t h e l i g a n d π-orbital i n t o o n e o f these; therefore, charge transfer b a n d s w i l l i n v o l v e o n l y t r a n s i t i o n to t h e a n t i b o n d i n g e *. g

b a n d p e a k i n g at 38,000 c m "

1

w i t h c o f 24,000 c m "

a t t r i b u t e d to s u c h t r a n s i t i o n b y Jorgensen.

T h e strong

M " for P t C l " was

1

1

6

T h e t r a n s i t i o n ir(t )

2

-> ^*

lu

leads to f o u r energy levels w h o s e p r i n c i p a l c o m p o n e n t s are T \ , *T*2 , T±u? 1

T .

3

2u

M

U

3

B e c a u s e o f the £i c h a r a c t e r o f the t r i p l e t s p i n f u n c t i o n s , transitions

to the p r i m a r i l y T , l

lu

T,

3

lu

states a l l h a v e some d i p o l e - a l l o w e d c h a r ­

T

3

2u

acter. H o w e v e r , n o r e s o l u t i o n i n t o s u c h i n d i v i d u a l states is possible w i t h the o b s e r v e d b a n d n o r c a n a n y d e c i s i o n b e presented as to w h e t h e r a contribution from ττ(ί ) -> e 2ΐί

g

occurs as w e l l .

T h e r e is t h e p o s s i b i l i t y

of a s y m m e t r y - f o r b i d d e n t r a n s i t i o n o f o n e o f t h e t

2g

e *. g

electrons i n t o t h e

T h e e x c i t e d e l e c t r o n i n e i t h e r o f t w o o r b i t a l s a n d the r e s i d u a l h o l e i n

a n y o f three leads to a t o t a l o f six singlet a n d six t r i p l e t states.

However,

these six states i n e a c h case constitute t w o t h r e e - f o l d degenerate sets; t h e l o w e r i n e n e r g y c a n b e d e s i g n a t e d as T

lg

a l l o w e d b a n d s s h o u l d o c c u r , therefore.

and a higher T .

T w o spin-

A s indicated w i t h

Jorgensens

2g

assignment i n F i g u r e 1, o n l y the first t r a n s i t i o n c a n b e seen as a s h o u l d e r o n the m u c h m o r e intense c h a r g e transfer b a n d . T h e s t i l l l o w e r intensities i n t h e r e g i o n o f 19,000 to 24,000 c m "

1

w i l l correspond then to t h e spin-

forbidden symmetry-forbidden bands.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

80

P L A T I N U M

G R O U P

M E T A L S

A N D

C O M P O U N D S

F o r the h e x a b r o m o p l a t i n a t e ( I V ) , there has b e e n a d e c i d e d shift of a l l b a n d s to l o w e r energies or l o n g e r w a v e l e n g t h s , a n d the b r e a d t h of the c h a r g e transfer b a n d definitely suggests m o r e t h a n a single e x c i t e d state. T h i s e n e r g y shift b e t w e e n c h l o r i d e a n d b r o m i d e l i g a n d s is q u i t e a g e n e r a l phenomenon

r e p r e s e n t i n g the p o s i t i o n of these l i g a n d s i n the

c h e m i c a l (sometimes

c a l l e d the F a j a n s - T s u c h i d a ) series.

spectro-

T h e shift of

t h e c h a r g e transfer b a n d reflects the easier o x i d a t i o n or loss of a n elec­ t r o n b y b r o m i d e i n c o m p a r i s o n w i t h c h l o r i d e . H o w e v e r , the shift i n the d-d t r a n s i t i o n represents the difference i n the c r y s t a l field s t r e n g t h of these t w o l i g a n d s . T h e I r C l " i o n , w i t h the same e l e c t r o n c o n f i g u r a t i o n as t h e 6

3

t w o p l a t i n u m complexes, h o w e v e r , is i n a l o w e r o x i d a t i o n state. A d d i t i o n a l e n e r g y is r e q u i r e d to a d d a n electron to the i r i d i u m , a n d

consequently

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

the charge transfer b a n d has b e e n f o r c e d to m u c h h i g h e r energies. the transitions to the t w o e x c i t e d states, p r i m a r i l y discernable. T h e occurrence

and T , 1

2g

Here,

are c l e a r l y

of the d-d b a n d s at l o w e r energies

corre­

sponds to a l o w e r Δ for I r ( I I I ) t h a n for P t ( I V ) , w h i c h is i n a c c o r d a n c e 0

w i t h the u s u a l systematics i n this q u a n t i t y (19). h i g h - i n t e n s i t y b a n d , 31,000-32,000

T h e b r e a d t h of

c m " , p r o b a b l y reflects 1

the

the

higher

s p i n - o r b i t c o u p l i n g of the b r o m i d e l i g a n d s i n c o m p a r i s o n w i t h that of chloride. F o r I r ( I V ) i n I r C l " , there is a h o l e i n the t 6

g r o u n d state, t

5

2g

2

— T . 2

2g

2g

one of t h e l i g a n d ττ-orbitals i n t o a t

2g

proposed

o r b i t a l set for the

T h e r e f o r e , the t r a n s i t i o n of a n e l e c t r o n f r o m o r b i t a l is possible. J o r g e n s e n

(17)

that these c h a r g e transfer b a n d s w e r e the ones seen i n the

v i s i b l e r e g i o n , 20,000-25,000 c m " , w h i c h h a d c's of 2 0 0 0 - 4 0 0 0 c m " M " . 1

1

1

T h e s e b a n d s p r o v i d e the intense color f o r I r C l " so t h a t its presence i n 6

2

m i n u t e amounts c a n b e d e t e c t e d e a s i l y i n solutions of I r C l " . e

T h e pres­

3

ence of h y p e r f i n e s t r u c t u r e o n the electron s p i n resonance s p e c t r u m of this ( 8 , 25)

i o n i n d i c a t e d t h a t the t

2g

orbitals were not solely metal

orbitals, b u t that t h e y c o n t a i n e d significant l i g a n d o r b i t a l character. T h i s feature

demonstrated

the

existence

of

some ττ-type

bonding

in

the

complex. F o r O s ( I V ) , there are t w o electrons m i s s i n g f r o m a filled set of orbitals. T h e r e f o r e , t r a n s i t i o n f r o m the l i g a n d ττ-orbitals to the t

2g

s h o u l d a g a i n b e possible.

Since O s ( I V )

t

2g

orbitals

is a m u c h w e a k e r o x i d i z i n g

agent t h a n I r ( I I I ) , i t is e x p e c t e d t h a t these c h a r g e transfer b a n d s w i l l b e s h i f t e d to h i g h e r energies.

T h e spectrum i n F i g u r e 1 indicates that

an a b s o r p t i o n p a t t e r n v e r y s i m i l a r to that f o r I r C l " occurs f o r O s C l " . 6

2

A c c o r d i n g l y , Jorgensen assigned the b a n d s f r o m 28,500-30,000 these L ->

t

2g

to b e o b s e r v e d .

6

cm"

1

2

to

transitions. T h e O s C l " s p e c t r u m is one of the r i c h e s t 6

2

S t i l l , o n l y a h a n d f u l of i n c o m p l e t e l y r e s o l v e d

b a n d s i n the s o l u t i o n s p e c t r u m are seen.

broad

Since a considerably larger

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

Ultraviolet

M A R T I N

Spectroscopic

81

Qualities

n u m b e r of s u c h c h a r g e transfer states m a y b e a t t a i n e d b y d i p o l e - a l l o w e d transitions t h a n are o b s e r v e d , a d e t a i l e d c o n f i r m a t i o n of this a s s i g n m e n t has not b e e n possible. Some v e r y r e c e n t i n f o r m a t i o n , w h i c h w i l l b e d i s ­ cussed later, has b r o u g h t this assignment of these b a n d s i n t o q u e s t i o n . F i g u r e 1 does s h o w t w o v e r y w e a k , r e l a t i v e l y s h a r p b a n d s t h a t o c c u r at a p p r o x i m a t e l y 17,000 c m "

1

for O s C l " w h i c h a r e not o b s e r v e d i n the

other s p e c t r a p r e s e n t e d .

T h e s e are b e l i e v e d to represent a t r a n s i t i o n

6

2

w i t h i n the g r o u n d state c o n f i g u r a t i o n — L e . , t* gTi( T ) 2

w e a k e r transitions (12)

3

-> Γ Ί ^ Α ^ ) .

lg

Still

h a v e b e e n o b s e r v e d at a b o u t 8000, 10,800, a n d

11,780 c m " . 1

M a n y features of t h e s p e c t r a of the o c t a h e d r a l complexes s e e m e d consistent w i t h s i m p l e m o l e c u l a r o r b i t a l m o d e l s .

have

The high sym­

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

m e t r y possessed b y these complexes f o r t u n a t e l y has r e d u c e d the n u m b e r of i n d i v i d u a l transitions w h i c h s h o u l d o c c u r because of the m a n y d e ­ generate states for the i o n . T h e broadness of the f e w b a n d s

observed,

h o w e v e r , p r e c l u d e s r e s o l u t i o n of the f a i r l y l a r g e n u m b e r of transitions w h i c h m i g h t b e e x p e c t e d to h a v e m e a s u r a b l e intensities as a c o n s e q u e n c e of s p i n - o r b i t c o u p l i n g .

T h e b r e a d t h of the a b s o r p t i o n b a n d s at least

p a r t i a l l y arises f r o m t h e r m a l l y e x c i t e d of the c o o r d i n a t i o n c o m p l e x .

fluctuations

i n the e n v i r o n m e n t

F o r e x a m p l e , i n the g r o u n d state a b o n d

m a y be lengthened b y a molecular vibration. T h e vibrational energy i n this m o d e w i l l a m o u n t to o n l y a b o u t kT.

H o w e v e r , because

of the

F r a n k - C o n d o n p r i n c i p l e , the e x c i t e d i o n w i l l h a v e the same i n t e r - a t o m i c distances as the g r o u n d state. T h u s , i f the e x c i t e d state i o n has a steep p o t e n t i a l e n e r g y f u n c t i o n for a t o m i c separations at the t r a n s i t i o n c o n ­ figuration,

a v i b r a t i o n a l d i s p l a c e m e n t of m o d e s t e n e r g y i n the g r o u n d

state w i l l p r o d u c e l a r g e energy differences i n the e x c i t e d c o m p l e x .

A

r e d u c t i o n i n t e m p e r a t u r e w i l l l e a d a c c o r d i n g l y to m u c h n a r r o w e r a n d better resolved bands.

Spectrum of

PtCl/'

T h e P t C l " i o n , w i t h the 2 + 4

a 5d

8

2

o x i d a t i o n state for p l a t i n u m , possesses

c o n f i g u r a t i o n . I t has a s q u a r e - p l a n a r c o o r d i n a t i o n , w h i c h is c o m ­

m o n l y o b s e r v e d w i t h the l o w s p i n complexes of this c o n f i g u r a t i o n .

Its

a b s o r p t i o n s p e c t r u m i n aqueous s o l u t i o n is also s h o w n i n F i g u r e 1.

With

the p l a t i n u m i n a l o w o x i d a t i o n state, the c h a r g e transfer b a n d s

have

b e e n s h i f t e d to b e y o n d 40,000 c m " . 1

S i n c e P t C l ~ absorbs so s t r o n g l y at 38,000 c m " , the a b s o r b a n c e 6

2

1

at

this w a v e n u m b e r c a n b e u s e d to set a v e r y l o w l i m i t of d e t e c t i o n o n the presence of P t ( I V ) i n samples of P t C l " . 4

2

T h i s is e s p e c i a l l y v a l u a b l e ,

since the h i g h e r o x i d a t i o n state has sometimes

been

suspected

catalyst f o r some of its reactions.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

as a

82

PLATINUM

GROUP

T h e m o l e c u l a r o r b i t a l scheme f o r t h e D

4h

METALS

AND COMPOUNDS

s y m m e t r y , possessed b y

this i o n , i s s h o w n i n F i g u r e 2. A l t h o u g h t h e i o n is h i g h l y s y m m e t r i c , the s y m m e t r y is sufficiently l o w that i n f o r m a t i o n f r o m p o l a r i z e d spectra of crystals is v e r y u s e f u l i n e s t a b l i s h i n g assignments f o r t h e transitions. T h e peaks at 25,400 a n d 30,300 c m " , w i t h e a b o u t 60, are c l e a r l y s p i n 1

a l l o w e d d-d transitions. I t w a s n o t c l e a r w h e t h e r t h e s m a l l e r p e a k a t a b o u t 20,000 c m " corresponds 1

s i m i l a r l y to a s p i n - a l l o w e d t r a n s i t i o n o r

to one w h i c h is s p i n - f o r b i d d e n . F i g u r e 2 shows a p o s s i b i l i t y o f three s p i n a l l o w e d transitions f r o m t h e filled d-orbitals i n t o t h e a n t i - b o n d i n g o r the d . 2

x

o r b i t a l . I n s u c h a t r a n s i t i o n , t h e e l e c t r o n leaves a s y m m e t r i c

2

y

( g ) o r b i t a l a n d moves i n t o a s y m m e t r i c ( g ) o r b i t a l , so t h e t r a n s i t i o n is therefore d i p o l e - f o r b i d d e n .

H o w e v e r , these transitions b e c o m e a l l o w e d

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

i n t h e presence o f a n a s y m m e t r i c the c h e m i c a l e n v i r o n m e n t — i . e . ,

field.

S u c h a field m a y r e s u l t f r o m

t h e effect o f n e i g h b o r i n g m o l e c u l e s o r

ions i n a s o l u t i o n o r i n a c r y s t a l . I t c a n also r e s u l t f r o m t h e a s y m m e t r i c vibrations of the complex. vibronically exicited.

I n t h e latter case, t h e t r a n s i t i o n is s a i d to b e

I n quantum mechanical description, the vibration

is c o n s i d e r e d a p e r t u r b a t i o n o n t h e system.

T h u s , t h e electronic

wave

f u n c t i o n , ^ i ct, is represented b y t h e e q u a t i o n e

e


(D

Σ Σ CQi ψu ψ„ 1

w h e r e ψ is t h e u n p e r t u r b e d f u n c t i o n , ψ is a n a s y m m e t r i c w a v e f u n c t i o n , 0

η

Q i is as a n a s y m m e t r i c n o r m a l v i b r a t i o n , a n d (2) I t i s necessary t o a n a l y z e t h e s y m m e t r y p r o p e r t i e s o f t h e n o r m a l vibrations of the complex

i n order to o b t a i n a set of selection rules.

Therefore, the spin-allowed transition of a n electron from the d

to the

xy

d . 2

x

2

y

o r b i t a l w i l l o c c u r w i t h t h e electric vector of l i g h t p o l a r i z e d i n t h e

d i r e c t i o n n o r m a l t o t h e s y m m e t r y axis—i.e., i n t h e xy p l a n e . T r a n s i t i o n s t a k i n g a n e l e c t r o n f r o m either t h e d

2

z

or d , xz

yz

o r b i t a l s t o t h e d -. x

y

will

o c c u r w i t h p o l a r i z a t i o n i n t h e ζ d i r e c t i o n a n d t h e xy d i r e c t i o n as w e l l . K PtCl 2

4

p r o v i d e s i d e a l crystals to test these conclusions.

e a c h P t C L t " o c c u p i e s a site w i t h f u l l D 2

ih

can b e introduced from the crystal s y m m e t r y (z)

I n t h e first p l a c e ,

s y m m e t r y (6), so n o asymmetries

fields.

E a c h i o n is a l i g n e d w i t h i t s

axis d i r e c t e d a l o n g t h e t e t r a g o n a l c-axis.

Crystals were

g r o w n as t h i n plates, < 50/x t h i c k , w i t h t h e c-axis l y i n g i n t h e face o f t h e plates. I t w a s possible t o measure t h e a b s o r p t i o n o f l i g h t p o l a r i z e d i n t h e ζ d i r e c t i o n a n d n o r m a l t o i t (20). T h e s e spectra are s h o w n i n F i g u r e 3, b o t h f o r r o o m t e m p e r a t u r e a n d w i t h l i q u i d h e l i u m c o o l i n g , n o m i n a l l y at 15 °K. A b a n d at ca. 26,000 c m " i n xy p o l a r i z a t i o n is c o m p l e t e l y m i s s i n g 1

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

Ultraviolet

M A R T I N

Spectroscopic

83

Qualities

120 100 80 60 40 *

s

20

γ" 0 5 100 ο ν

80

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

60 40 20 0 1.4

1.6

1.8

2.0 22

2.4 2.6 2.8

Ι Ο " χ ν χ CM" spectra of a K PtCl light 4

Figure

3.

Absorption

3.0

3.2

3.4 3.6

1

2

crystal with

/t

polarized

Crystal thickness, 46 microns

w i t h the ζ p o l a r i z a t i o n . T h i s appears t o b e a rigorous selection r u l e a n d identifies that b a n d as associated w i t h the d

xy

-» d -. - t r a n s i t i o n . I n c i ­ x

y

d e n t a l l y , the c r y s t a l spectra i d e n t i f i e d the b a n d at 20,000 c m "

as d u e t o

1

s p i n - f o r b i d d e n transitions. I f i t w e r e a s p i n - a l l o w e d t r a n s i t i o n , t h e n the t h e o r y w o u l d r e q u i r e a n o b s e r v a b l e s p i n - f o r b i d d e n b a n d i n the r e g i o n o f 11,000-14,000

cm" . 1

N o s u c h a b s o r p t i o n was o b s e r v e d

i n this r e g i o n ,

e v e n for crystals 1 m m t h i c k . A s s i g n m e n t o f the b a n d at a b o u t 30,000 c m

was achieved from a

- 1

m e a s u r e m e n t of the m a g n e t i c c i r c u l a r d i c h r o i s m ( M C D ) . W h e n a spe­ cies w i t h a nondegenerate g r o u n d state absorbs l i g h t to f o r m a degenerate e x c i t e d state, t h e degeneracy

w i l l be broken b y the Zeeman

splitting.

A characteristic M C D s p e c t r u m results w i t h a n i n v e r s i o n i n s i g n o f the m e a s u r e d A —A R

L

o c c u r r i n g n e a r t h e absorbance

maximum.

This has

b e e n assigned the Α-term i n the t h e o r e t i c a l treatment o f Stephens

(26).

T h e M C D s p e c t r u m i n F i g u r e 4 shows just this c h a r a c t e r i s t i c f o r m asso­ c i a t e d w i t h the b a n d at 30,000 c m " . 1

H e n c e , i t c a n b e assigned t o the

transitions f r o m t h e degenerate p a i r o f orbitals d , xz

A t l o w temperatures, n a r r o w e r b a n d s

yg

->

d . . 2

x

2

y

w i t h better r e s o l u t i o n a r e

expected, a n d the v i b r o n i c m o d e l p r e d i c t s l o w e r intensities as w e l l . T h e p o l a r i z e d spectra at l i q u i d h e l i u m temperatures c o n f i r m these p r e d i c t i o n s . T h u s , shoulders a t 24,000 c m "

1

a n d i n the r e g i o n o f 17,000-19,000

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

cm"

1

PLATINUM

84

GROUP

METALS

AND

w h i c h c o u l d not b e r e s o l v e d at r o o m t e m p e r a t u r e n o w clearly.

COMPOUNDS

are r e s o l v e d

A n i n t e r e s t i n g feature is the fine s t r u c t u r e w h i c h a p p e a r e d o n

t h e t w o b a n d s f r o m 23,000-28,000 c m " , w h e r e 17 i n d i v i d u a l p e a k s c a n b e 1

seen.

T h e s e i n d i v i d u a l peaks result f r o m e x c i t a t i o n of the t o t a l l y s y m ­

m e t r i c , b r e a t h i n g v i b r a t i o n i n the e x c i t e d

electronic

states.

Weaker

v i b r a t i o n a l structure c o u l d b e d i s c e r n e d , e s p e c i a l l y i n ζ p o l a r i z a t i o n for the b a n d c e n t e r e d o n 20,600 c m " . 1

H o w e v e r , n o s u c h structure w a s

e v i d e n t o n t h e strong b a n d a t 29,600 c m " . 1

A n i n t e r e s t i n g conjecture

is t h a t b a n d s for w h i c h t h e v i b r a t i o n a l

structure is m i s s i n g i n v o l v e transitions to e x c i t e d electronic states w h i c h

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

60

Έ υ 7

40 * 20 0

+

2.0

«•

Ο

< <

l

-2.0

300

400

500

WAVE LENGTH π\μ Figure 4. Absorption spectrum and magnetic circular dichroism for a solution of K PtCl, in dilute aqueous HCl 2

Cell length, 1.00 cm Concn. KJtCU, 0.015M

correlate w i t h states of l o w e r energy i n t e t r a h e d r a l c o o r d i n a t i o n of the ligands.

O n e of the o u t - o f - p l a n e b e n d i n g v i b r a t i o n s carries the s q u a r e -

p l a n a r c o o r d i n a t i o n t o w a r d the t e t r a h e d r a l . C o n s e q u e n t l y , a h a r m o n i c p o t e n t i a l energy f u n c t i o n f o r this v i b r a t i o n w o u l d not a p p l y .

Such a

c o n s e q u e n c e w o u l d l i k e l y p r o v i d e m a n y m o r e p o s s i b l e v i b r a t i o n a l states i n t h e e x c i t e d state. T h e a b u n d a n c e of closely s p a c e d states w h i c h are t h e n possible prevents t h e i r r e s o l u t i o n b y the t e c h n i q u e e m p l o y e d . T h e energy of the t r a n s i t i o n f r o m the d

2

z

to t h e ά *- * χ

2

ν

is n o t i n d i c a t e d

f r o m the o b s e r v e d spectra. H o w e v e r , the 1-electron o r b i t a l energies c a l -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

Ultraviolet

M A R T I N

Spectroscopic

85

Qualities

culated from theory b y B a s c h a n d G r a y (2) a n d b y C o t t o n a n d Harris p l a c e t h e d * o r b i t a l w e l l b e l o w the degenerate d ,d e

xz

(4)

orbitals. There­

yz

fore, t h e y h a v e assigned a b s o r p t i o n i n the r e g i o n of 38,000-40,000

cm"

1

o n t h e t a i l of c h a r g e transfer b a n d s to this t r a n s i t i o n . T h e energy states for a d

system c a n b e c a l c u l a t e d f r o m a set of

s

parameters i n c l u d i n g the s p l i t t i n g of the d - o r b i t a l s , the e l e c t r o n - e l e c t r o n r e p u l s i o n p a r a m e t e r s ( e i t h e r those of S l a t e r a n d C o n d o n or of

Racah)

a n d the s p i n - o r b i t c o u p l i n g . I n F i g u r e 5 are p r e s e n t e d the results of s u c h a c a l c u l a t i o n , w i t h t h e p a r a m e t e r s a d j u s t e d to assign t r a n s i t i o n s w i t h e x p e c t e d h i g h i n t e n s i t y to t h e o b s e r v e d b a n d s .

T h e results of a c o r r e ­

s p o n d i n g c a l c u l a t i o n for the t e t r a h e d r a l a r r a n g e m e n t are s h o w n also.

K Ptci

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

2

5d

4

35000 U

—

*

r

~

\

_

30000

2 5 0 0 0 \-

Α

2 ς ^ - . ^ - ^ "

X

'Τ 5 —

/

2 c

y

3R

h

\

\

Γ

-=

20000

e

^

~

~

'

Z

j

r

-

N

^

15000 \/ / /

cm" i

0

3000

/

•Δ

<

/ D

'

4h

T

d

Figure 5. Calculated energy levels for the PtCl, ' ion in D and T symmetry. In the center, the energy levels are shown for D coordination with the inclusion of a spin-orbit coupling parameter: ζ = 3000 cm' . The states are designated with the Γ notation for the D / double group, which applies with the inclusion of spinorbit coupling. For D : d * — d = 26,100 cm' ; à .y ~ d = 30,200 cm ; d * _ / ~ <* = > cm' , F = 1000 cm' , F = 65 cm' . For the T coordination, A = 14,000 cm' , F = 1000 cm' , and F = 65 cm' . Observed bands for the crystal are shown at the right side 2

t

ih

d

ih

1

4 h

2

2

x

1

x z

x

2

1

2

t

y

1

x y

11

y z

2 z

x

3 8

1

4

1

2

3 0 0

d

1

à

1

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

86

P L A T I N U M

I

I

I

I

15

I

I

I

I

I

G R O U P

20 I0" x V

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

6. Absorption Salt, Pt(NH ) PtCl 3 A

i9

I

I

I

I

25 3

Figure

I

I

M E T A L S

cm"

A N D

I

C O M P O U N D S

I

30 1

spectrum of Magnus' Green with polarized light

It is possible to select a v a l u e of the p a r a m e t e r Δ* so t h a t w i t h the i n d i ­ c a t e d values of F

2

a n d F the b a n d s w i t h h i g h v i b r a t i o n a l s t r u c t u r e at l o w 4

t e m p e r a t u r e correlate w i t h m u c h h i g h e r energy states i n t h e t e t r a h e d r a l s y m m e t r y . T h i s figure illustrates the p o i n t that s p i n - o r b i t c o u p l i n g m u l ­ tiplies t h e n u m b e r of separated energy states. E v e n w i t h large s p i n - o r b i t c o u p l i n g s of the h e a v y p l a t i n u m elements, w h i c h p r o v i d e the i n t e n s i t y for these s p i n - f o r b i d d e n transitions, the s p l i t t i n g of the m a n y states is n o t sufficient for t h e i r i n d i v i d u a l r e s o l u t i o n f r o m the e x p e r i m e n t a l s o l u ­ t i o n spectra w h e r e o n l y a f e w b r o a d areas of a b s o r p t i o n c a n b e i d e n t i f i e d . Professor S c h a t z a n d c o w o r k e r s

(23)

at the U n i v e r s i t y of V i r g i n i a

h a v e e x t e n d e d the M C D studies i n t o the charge transfer b a n d r e g i o n . H e r e also, t h e y i d e n t i f y a d e g e n e r a c y f o r the e x c i t e d states, w h i c h p r e ­ s u m a b l y arises f r o m

a t r a n s i t i o n a l electron l e a v i n g a n e (ir)

orbital.

u

H o w e v e r , t h e y c o n c l u d e d t h a t the strongest o b s e r v e d b a n d at 46,200 c m "

1

c o r r e s p o n d e d to a 5d - » 6p t r a n s i t i o n . T h e a b s o r p t i o n b a n d s for the crystals of K P t C l 2

the solutions i n b o t h i n t e n s i t y a n d energy.

4

resemble those of

T h e r e is little d o u b t t h a t for

the c r y s t a l the o b s e r v e d spectra are c a u s e d b y i s o l a t e d ions w h i c h are n o t i n f l u e n c e d s u b s t a n t i a l l y b y n e i g h b o r i n g ions.

I n these crystals, the

p l a n a r ions are s t a c k e d one a b o v e the other w i t h a s e p a r a t i o n of 4.21A. T h e p o t a s s i u m ions p a c k i n the planes b e t w e e n the ions w i t h to

the

external portion

of

the

chloride

ligands.

I n the

contacts

compound

P t ( N H ) P t C l , M a g n u s ' green salt ( M G S ) , there are s t r i k i n g differences 3

4

4

i n the spectra.

I n M G S , the c a t i o n a n d anions stack alternately w i t h a

s e p a r a t i o n of o n l y 3.25A a l o n g a n e e d l e axis of the c r y s t a l . T h e s e needles are strongly d i c h r o i c , w i t h a m a x i m u m a b s o r p t i o n i n the v i s i b l e i n the d i r e c t i o n of the stacked chains. P o l a r i z e d spectra, w h i c h w e r e r e p o r t e d

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

Ultraviolet

M A R T I N

Spectroscopic

87

Qualities

b y D a y et al. ( 5 ) , are s h o w n i n F i g u r e 6. S i n c e a b s o r p t i o n b a n d s of the ion P t ( N H ) 3

4

2 +

o c c u r at h i g h e r energies t h a n for P t C l " , the s p e c t r u m 4

2

of M G S is b e l i e v e d to represent t h a t of the P t C U " i o n as m o d i f i e d b y t h e 2

close presence of the cations. T h e h i g h a b s o r p t i o n i n the ζ d i r e c t i o n is e v i d e n t f r o m F i g u r e 6. H o w e v e r , the intense green results f r o m a r a t h e r n o r m a l a b s o r p t i o n b a n d at 16,500 c m " w i t h a w i n d o w at 20,000 c m " i n 1

1

the s p e c t r u m for a c o o r d i n a t i o n c o m p l e x .

T h e r e is n o e v i d e n c e f o r a n

a b s o r p t i o n c o n t i n u u m characteristic of a c o n d u c t i o n t y p e b a n d .

How­

ever, the h i g h a b s o r p t i o n i n the ζ d i r e c t i o n has b e e n c o n s i d e r e d a c o n ­ sequence of

a p e r t u r b a t i o n of the states for

PtCLi ". 2

A

z-polarized,

d i p o l e - a l l o w e d t r a n s i t i o n is m o v e d to l o w e r energies closer to the transitions.

Consequently,

greater i n t e n s i t y for

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

b o r r o w e d u n d e r the v i b r o n i c m e c h a n i s m (1, 5,

z-polarization can

d-d be

24).

Effects of Reduction in Symmetry If one of the c h l o r i d e l i g a n d s i n P t C U " is r e p l a c e d b y another g r o u p , 2

the center of s y m m e t r y i n the i o n is r e m o v e d .

I n F i g u r e 7 are s h o w n

spectra i n the r e g i o n of 25,000-40,000 c m " f o r t h e ions P t C l ( H 0 ) - a n d 1

PtCl (NH )~. 3

3

3

2

T h i s is the r e g i o n for the s p i n - a l l o w e d d-d b a n d s of these

ions. I n a c c o r d a n c e w i t h the c o n c e p t t h a t a m m o n i a has a stronger c r y s t a l field effect t h a n H 0 , w h i c h is stronger t h a n t h a t of c h l o r i d e , b a n d s are 2

s h i f t e d to h i g h e r energy b y the s u b s t i t u t i o n of a c h l o r i d e b y w a t e r a n d to s t i l l h i g h e r energy u p o n s u b s t i t u t i o n b y a m m o n i a .

S i n c e there is n o

center of s y m m e t r y i n these ions, the presence of the l i g a n d s creates a n a s y m m e t r i c electric field at the p l a t i n u m a t o m .

T h e h i g h e r intensities

of the b a n d s seem to b e a n a t u r a l c o n s e q u e n c e of these a s y m m e t r i c

fields.

O n e p u z z l i n g feature for w h i c h there appears to b e n o r e a d y e x p l a n a t i o n is the r e l a t i v e intensities of t h e t w o b a n d s i n the three complexes. P t C l ~ , the c's of the t w o s p i n - a l l o w e d peaks are a b o u t e q u a l . 4

2

For

I n the

P t C l ( H 0 ) " , the h i g h energy b a n d is m u c h m o r e intense t h a n the l o w e n ­ 3

2

e r g y b a n d , whereas for the P t C l ( N H ) " , just the reverse s i t u a t i o n occurs. 3

If a s a m p l e of K P t C l 2

4

3

is d i s s o l v e d i n w a t e r w i t h n o a d d i t i o n a l c h l o ­

r i d e , a n d the absorbance of t h e s o l u t i o n is f o l l o w e d at 25,500 cm" —i.e., 1

at the m a x i m u m of the first s p i n - a l l o w e d b a n d — t h e absorbance falls a n d the m a x i m u m shifts t o w a r d l o n g e r w a v e l e n g t h s as the s p e c t r u m

changes

c o n t i n u o u s l y t o w a r d the s p e c t r u m of the P t C l ( H 0 ) " . A t e q u i l i b r i u m 3

2

w i t h respect to the a q u a t i o n r e a c t i o n P t C l ~ + H 0 -> P t C l ( H 0 ) - + C I " 4

2

2

3

(3)

2

the s p e c t r u m is i n t e r m e d i a t e b e t w e e n the t w o s h o w n i n F i g u r e 7.

The

s p e c t r u m for P t C l ( H 0 ) " w a s o b t a i n e d f r o m the o b s e r v e d e q u i l i b r i u m 3

2

s p e c t r u m a n d the e q u i l i b r i u m concentrations of the species.

T h e spec-

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

88

P L A T I N U M

10

Figure 7.

χ

M E T A L S

A N D

C O M P O U N D S

χ cm"

Absorption spectrum in dilute aqueous HCl of the com­ plexes, PtClf', PtCl (H 0); and PtCl (NH )s

6.00 X I0~

(5

3

M

Rb PtBr 2

8.

3

s

4

BQJJ

40

2

160

TIME IN

Figure

ν

GROUP

180

2ÔÔ

220

MINUTES

Changes in the absorbance solved in H 0

after RbzPtBr^

is dis-

2

Wavelength, 415

πΐμ.

NaNOs added to give an ionic strength of 0.318M. H\ 10- M. S

t r u m of t h e P t C L t " i o n c a n b e e v a l u a t e d f a i r l y a c c u r a t e l y i n solutions 2

w i t h h i g h c h l o r i d e concentrations. A s i m i l a r effect w a s e x p e c t e d for a s o l u t i o n of P t B r " at the c o r r e ­ 4

2

s p o n d i n g b a n d w h i c h occurs at 24,400 c m " . H o w e v e r , i n s u c h a s o l u t i o n , 1

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

M A R T I N

Ultraviolet

Spectroscopic

89

Qualities

as s h o w n i n F i g u r e 8, a l t h o u g h there was i n i t i a l l y a v e r y s m a l l decrease i n the a b s o r b a n c e , this decrease w a s f o l l o w e d b y a m u c h l a r g e r increase (27).

U p o n the a d d i t i o n of excess b r o m i d e i o n , the a b s o r b a n c e r e t u r n e d

to its i n i t i a l v a l u e w i t h a p e r i o d of a b o u t 5 m i n .

This behavior

was

a t t r i b u t e d to the f o r m a t i o n of the P t B r " d i m e r i c i o n i n t h e s o l u t i o n . 2

6

2

T h i s i o n h a d b e e n i d e n t i f i e d p r e v i o u s l y b y H a r r i s et al. ( 9 ) .

The data

i n F i g u r e 8 p r o v i d e d i n f o r m a t i o n a b o u t the rate of f o r m a t i o n a n d r e a c t i o n of this d i m e r . A p p a r e n t l y a n a q u a t i o n r e a c t i o n PtBr ~ + 4

H 0 -> P t B r ( H 0 ) - + B r ~

2

2

3

(4)

2

occurs i n i t i a l l y , b u t this process is f o l l o w e d b y the r e a c t i o n 2 P t B r ( H 0 ) - -> P t B r Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

3

2

2

2

6

- +

2H 0

(5)

2

T h i s d i m e r i c i o n c a n be c o n s i d e r e d i n e q u i l i b r i u m w i t h P t B r ~ i n a c c o r d 4

2

ance w i t h the r e a c t i o n 2 P t B r ~ <=> P t B r 4

2

2

6

2

- +

2Br~

(6)

S i n c e i n the f o r m a t i o n of P t B r " f r o m P t B r ~ t w o b r o m i d e 2

6

2

4

2

ions

are

f o r m e d , there w i l l be a h i g h e r f r a c t i o n of the p l a t i n u m c o n v e r t e d to the d i m e r at h i g h e r d i l u t i o n . F i g u r e 9 illustrates the spectra r e c o r d e d i n a n e x p e r i m e n t i n w h i c h a s o l u t i o n of H P t B r 2

2

was diluted. T h e initial solu-

6

t i o n h a d b e e n f o r m e d b y p a s s i n g the t e t r a e t h y l a m m o n i u m salt of P t B r " 2

t h r o u g h a c a t i o n exchanger i n the h y d r o g e n phase.

6

2

U p o n d i l u t i o n , the

a b s o r b a n c e d e c r e a s e d t o w a r d a s p e c t r u m to be e x p e c t e d for the P t B r 3

( H 0 ) ~ i o n . W i t h the a d d i t i o n of excess K B r , the o b s e r v e d s p e c t r a c o i n 2

c i d e d w i t h that of P t B r " . 4

2

T h e o b s e r v e d s p e c t r a l changes i n d i c a t e d t h a t

the f o r m a t i o n of t h e d i m e r i c species, P t B r " , was too s l o w to a c c o u n t for 2

6

2

the i s o t o p i c exchange b e t w e e n free b r o m i d e i o n a n d the b r o m i d e l i g a n d s i n P t B r " , even t h o u g h the kinetics for s u c h e x c h a n g e i n c l u d e d a t e r m 4

2

w h i c h was s e c o n d o r d e r i n c o m p l e x . I t was c o n c l u d e d that s u c h e x c h a n g e o c c u r r e d t h r o u g h the m a k i n g a n d b r e a k i n g of s i n g l y

bromide-bridged

d i m e r i c complexes.

Spectra

in Organic

Media

A l t h o u g h t h e v i s i b l e a n d u l t r a v i o l e t spectra of the p l a t i n u m m e t a l c o m p l e x e s serve as a v a l u a b l e means to f o l l o w t h e i r reactions, this feature is e s p e c i a l l y d i s t u r b i n g to one w h o is t r y i n g to establish the e n e r g y states for a p a r t i c u l a r species.

S o m e care is necessary

to e s t a b l i s h that t h e

m e a s u r e d s p e c t r u m results f r o m the p a r t i c u l a r c o m p l e x species of interest, a n d not some of its r e a c t i o n p r o d u c t s .

W a t e r is a n effective n u c l e o p h i l e

for these complexes.

T o a v o i d s o l v a t i o n of some p l a t i n u m c o m p l e x e s ,

M a s o n a n d G r a y (21)

h a v e r e c e n t l y r e p o r t e d spectra of t h e t e t r a b u t y l -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

PLATINUM

GROUP

METALS

AND

COMPOUNDS

Figure 9. Spectral changes when an aged solution of H Pt Br in a 1-cm cell (0 min) is diluted 10-fold and added to a 10-cm cell 2

2

6

Dashed curve obtained after the addition of solid KBr. Temp., 25°. NaN0 added to give ionic strength of 0.318M. 3

Figure 10. Spectrum of (NBu ) PtBr^ in a 2:1 mixture of 2-methyltetrahydrofuran and propionitrile at room temperature and at 77° Κ (liquid nitrogen) u 2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

MARTIN

Ultraviolet

Spectroscopic

a m m o n i u m tetrabromoplatinate (II)

91

Qualities

i n a n o r g a n i c solvent m e d i u m c o n ­

sisting of 2 : 1 m i x t u r e of 2 - m e t h y l t e t r a h y d r o f u r a n a n d p r o p i o n i t r i l e . I n this w a y s o l v a t i o n w a s a v o i d e d . I n a d d i t i o n , t h e y w e r e a b l e to c o o l these solutions as glasses to l i q u i d n i t r o g e n temperatures. T h i s p r o v i d e d m u c h better r e s o l u t i o n of t h e a b s o r p t i o n b a n d s , as is s h o w n i n t h e i r spectra i n F i g u r e 10. Shoulders at 26,500 a n d 33,000 c m the l o w e r temperatures.

- 1

are c l e a r l y r e s o l v e d at

S i n c e v i b r o n i c e x c i t a t i o n is r e d u c e d at l o w e r

temperatures, intensities of t h e s y m m e t r y - f o r b i d d e n b a n d s i n t h e r e g i o n of 20,000-30,000 c m '

1

are l o w e r at t h e l i q u i d n i t r o g e n temperatures. T h e

d i p o l e - a l l o w e d transitions, o n t h e other h a n d , possess a t e m p e r a t u r e i n d e p e n d e n t t o t a l i n t e n s i t y . T h e r e f o r e , as t h e b a n d s n a r r o w at l o w t e m ­

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

p e r a t u r e , e x t i n c t i o n coefficient peaks b e c o m e h i g h e r .

T h i s is e s p e c i a l l y

Ε ο vu >ι-

α ο (/)

ω

< < -J Ο

2

20000

25000 Z/cnrf

30000

35000

1

Figure 11. Absorption spectrum of Pt(en)Cl in an aqueous 0.3M Cl~ solution and in single crystals with polarized light at 300°Κ and at liquid helium tem­ peratures (nominally 15°K) 2

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

92

PLATINUM

GROUP

METALS

A N D COMPOUNDS

e v i d e n t i n t h e i r spectra f r o m 33,000-38,000 c m " , the r e g i o n o f the h i g h 1

i n t e n s i t y charge transfer b a n d s .

Spectrum of Diehlorο (ethylene diamine) platinum (II). Metal—Metal Interactions

Evidence for

W e h a v e r e c e n t l y o b t a i n e d some i n t e r e s t i n g spectra o f the n e u t r a l c o m p l e x P t ( e n ) C l . T h e s o l u t i o n s p e c t r u m of this c o m p l e x i n the r e g i o n 2

of the d-d b a n d s i s s h o w n i n F i g u r e 11. T h e charge transfer b a n d s are b e y o n d 48,000 c m " .

Its s o l u t i o n s p e c t r u m is v e r y s i m i l a r t o t h a t of

1

P t ( N H ) C l 2 , except t h a t the m o l a r a b s o r p t i v i t y i n the r e g i o n o f t h e 3

2

a b s o r p t i o n m a x i m u m is t w i c e as h i g h f o r the c i s - d i c h l o r o d i a m m i n e p l a t i -

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

num(II).

C h a t t , G a m l e n , a n d O r g e l ( 3 ) h a v e assigned the s p e c t r u m o f

t h e d i c h l o r o d i a m m i n e c o m p l e x o n t h e basis o f D

4 f e

symmetry, considering

the l i g a n d field d i s t o r t i o n t o b e a m i n o r effect. T h e p e a k at 33,000 c m " w a s assigned as the first s p i n - a l l o w e d d-d b a n d — i . e . , d

xy

b a n d for d , xz

yz

-> d* *. x

2

y

1

-» d* . . T h e 2

x

2

y

w a s c o n s i d e r e d the s h o u l d e r t o the h i g h energy

side o f this peak. T h e r e w e r e t h e n t w o f a i r l y w e l l r e s o l v a b l e s p i n - f o r b i d ­ d e n b a n d s at l o n g e r w a v e l e n g t h s . T h e c r y s t a l s t r u c t u r e o f P t ( e n ) C l

2

was

recently determined b y x-ray diffraction methods b y Jacobson a n d Benson i n our laboratory ( I I ) .

T h e y f o u n d that the crystals b e l o n g e d

to t h e

o r t h o r h o m b i c system w i t h the molecules stacked i n a n e a r l y l i n e a r a r r a y , as s h o w n i n F i g u r e 12, w i t h a u n i f o r m s p a c i n g o f 3.39A b e t w e e n t h e

A

Β

Figure 12. A. Stacking of Pt(en)Cl molecules in the orthorhombic cry stab. B. Anticipated order of 1-electron orbital energies with their symmetry designations for the à-orbitals under the D and the C groups. 2

ih

2y

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

7.

MARTIN

Ultraviolet

p l a t i n u m atoms.

Spectroscopic

93

Qualities

T h i s s p a c i n g is o n l y 0.14A greater t h a n b e t w e e n t h e

ions i n M G S . V e r y t h i n crystals, <

10μ t h i c k , w i t h the c a n d b axes

l y i n g i n the faces w e r e a v a i l a b l e so that l i g h t d i r e c t e d a l o n g the a axis p e r m i t t e d the o b s e r v a t i o n o f s p e c t r a p o l a r i z e d i n the b- a n d c-directions ( F i g u r e 12).

T h e s e p o l a r i z e d spectra are s h o w n i n F i g u r e 11. A t r o o m

t e m p e r a t u r e , t h e a b s o r p t i o n i n the c - d i r e c t i o n w a s m u c h h i g h e r t h a n for t h a t w i t h b - p o l a r i z a t i o n . A t 25,000 c m " , f o r e x a m p l e , the b - p o l a r i z a t i o n 1

is o f the o r d e r o f that i n s o l u t i o n , whereas i n the c - d i r e c t i o n i t has b e e n enhanced ten-fold.

I n its i n t e n s i t y features, these spectra strongly r e ­

semble those of M G S , a l t h o u g h there has not b e e n a shift of b a n d s t o longer w a v e l e n g t h s f r o m the s o l u t i o n spectra. A t l o w e r temperatures, t h e e x p e c t e d n a r r o w i n g o f b a n d s has b e e n o b s e r v e d , a n d f o r t h e c - p o l a r i z a -

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

t i o n three components are easily r e s o l v a b l e w i t h l o w e r intensities t h a n a t room temperature.

H o w e v e r , f o r the b - p o l a r i z a t i o n — i . e . , n o r m a l t o t h e

s t a c k i n g d i r e c t i o n — w i t h a n a r r o w i n g o f the a b s o r p t i o n b a n d , there has b e e n a n increase i n the h e i g h t o f the peak.

T h i s b e h a v i o r is that o f a

s y m m e t r y - a l l o w e d t r a n s i t i o n o f the sort w h i c h w e r e o b s e r v e d i n the l o w t e m p e r a t u r e spectra o f M a s o n a n d G r a y (21).

S i n c e the m o l e c u l e does

not possess a center o f s y m m e t r y , the possible effects o f the a s y m m e t r i c l i g a n d field w e r e e x a m i n e d . I f a p l a n a r c o n f i g u r a t i o n w a s a s s u m e d , w h i c h is not s t r i c t l y t r u e because o f p u c k e r i n g o f the chelate r i n g , b u t w h i c h is not a b a d a p p r o x i m a t i o n , a n a s y m m e t r i c

field

i n the direction of the

m o l e c u l a r d i p o l e w o u l d p r o v i d e some d i p o l e - a l l o w e d i n t e n s i t y f o r t h e d

xz

-> d * t r a n s i t i o n . H o w e v e r , this w o u l d b e for p o l a r i z a t i o n i n the z, o r xy

c - d i r e c t i o n . H e n c e , the presence of a n a l l o w e d t r a n s i t i o n n o r m a l t o the c h a i n d i r e c t i o n w o u l d not b e e x p e c t e d f r o m this source. N o t e that, as s h o w n i n F i g u r e 12, the χ a n d y axes h a v e b e e n d i r e c t e d b e t w e e n the l i g a n d s so that the a n t i b o n d i n g o r highest d - o r b i t a l is d e ­ s c r i b e d as the d

xy

rather than the d . 2

x

2

y

w h i c h w a s u s e d i n the section o n

the P t C l " i o n . T h e assignment o f the χ a n d y axes is a r b i t r a r y b e t w e e n 4

2

t w o e q u i v a l e n t choices i n D

s y m m e t r y , a n d i n t e r c h a n g e o f t h e choices

4h

interchanges the b a n d b representations. 1

2

F o r this c o m p o u n d the p r e s ­

ent c h o i c e was c o n v e n i e n t , since the χ a n d y axes w e r e t h e n d i r e c t e d i n the d i r e c t i o n o f the o r t h o r h o m b i c axes a n d the y axis w a s d i r e c t e d a l o n g the C

2

s y m m e t r y axis o f t h e m o l e c u l e .

T h e consequences o f energy b a n d f o r m a t i o n f r o m i n t e r a c t i o n s o f electrons i n the p l a t i n u m d-orbitals o n l y w e r e c o n s i d e r e d . the d - o r b i t a l s , say the d

2

z

F o r a set o f

o r b i t a l o n e a c h p l a t i n u m a t o m i n the c h a i n ,

w e r e f o r m e d a n L C A O w a v e f u n c t i o n o f the f o r m

Ψη(* ) =

Σ

2

i

C .y(<«y n

= l

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

(7)

94

PLATINUM

GROUP

METALS

AND

COMPOUNDS

where Ν Σ C ».y = 1 =ι

(8)

2

i

a n d (ai)j is t h e d

2

z

o r b i t a l o f t h e / a t o m i n a c h a i n o f η-platinum atoms.

F r o m application of the simple theory of a particle i n a one-dimensional box

jf + i

WTT)

s i n

( 9 )

w h e r e η c a n b e a n integer, 0 < η < Ν -f- 1. W i t h v e r y large N, w h e r e

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

o n l y i n t e r a c t i o n s b e t w e e n adjacent atoms are c o n s i d e r e d , E

# <M τ = H

=

n

j3

+ 2H

jtj

+

T h u s , a b a n d o f e n e r g y states b a s e d o n the d

2

z

l C

os

(10)

o r b i t a l s is p r e d i c t e d . A

c o r r e s p o n d i n g set o f w a v e functions, d e s c r i b i n g s i m i l a r b a n d s , c a n b e w r i t ­ t e n for e a c h o f the other f o u r d - o r b i t a l s . W i t h the a t o m i c d c o n f i g u r a t i o n 8

of P t , t h e f o u r l o w e s t b a n d s are filled; the h i g h e s t b a n d , b a s e d o n the 2 +

a n t i b o n d i n g o r b i t a l i n v o l v i n g d , is e m p t y . T h e expression for the t r a n s i ­ xy

t i o n m o m e n t i n v o l v i n g a transfer of a n e l e c t r o n f r o m ψ i n a filled b a n d t o η

ij/m i n the e m p t y b a n d r e q u i r e s a n e v a l u a t i o n o f t h e d i p o l e m o m e n t i n t e g r a l Ρ η — m = Jψη(ζ*>

ψ™ (xy) dz

(11)

F r o m the s y m m e t r y p r o p e r t i e s of the p r o d u c t s i n these integrals, i t c a n b e c o n c l u d e d t h a t transitions f r o m the d

2

z

d 2. 2 X

y

b a n d t o the d*

xy

f r o m the d

xz

b a n d t o the d*

xy

a n d f r o m the d

yz

tion.

b a n d t o the d*

b a n d are d i p o l e - f o r b i d d e n .

xy

a n d f r o m the

However, a transition

b a n d is d i p o l e - a l l o w e d i n t h e y p o l a r i z a t i o n

b a n d t o t h e d*

xy

b a n d is d i p o l e - a l l o w e d i n the χ d i r e c ­

Therefore, t h e b a n d theory predicts a dipole-allowed transition

n o r m a l to the c h a i n f r o m t h e b a n d s a r i s i n g f r o m the o r b i t a l s w h i c h are degenerate

(e ) g

in D

4h

symmetry.

S i n c e p r e s u m a b l y interactions o f the

electrons b e t w e e n the p l a t i n u m atoms are not l a r g e , the b a n d is n a r r o w a n d o f l o w i n t e n s i t y . H o w e v e r , the b a n d t h e o r y does a c c o u n t v e r y n i c e l y for the o b s e r v e d d i p o l e - a l l o w e d t r a n s i t i o n i n y p o l a r i z a t i o n .

Direction of Current Research I n the p r e c e d i n g sections, a n u m b e r o f specific instances h a v e b e e n r e v i e w e d i n w h i c h the a b s o r p t i o n s p e c t r a o f p l a t i n u m g r o u p complexes h a v e p r o v i d e d i n f o r m a t i o n c o n c e r n i n g t h e c h e m i c a l b e h a v i o r o f t h e sys­ tems a n d the e l e c t r o n i c s t r u c t u r e a n d b o n d i n g i n the c o m p o u n d s .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Some

7.

MARTIN

Ultraviolet

Spectroscopic

95

Qualities

d e v e l o p m e n t s , p u b l i s h e d v e r y r e c e n t l y , also deserve m e n t i o n , since t h e y illustrate t h e d i r e c t i o n i n w h i c h t h e research is m o v i n g . R e c e n t l y , Professor S c h a t z a n d c o w o r k e r s at t h e U n i v e r s i t y of V i r ­ g i n i a h a v e r e p o r t e d m a g n e t i c c i r c u l a r d i c h r o i s m spectra f o r t h e I r C l " 6

i o n i n b o t h s o l u t i o n a n d single crystals (10, 22).

3

I n addition, they have

refined t h e t h e o r y , i n c l u d i n g t h e d e s c r i p t i o n of t h e d - o r b i t a l s , sufficiently that t h e y c a n p r e d i c t t h e s i g n of t h e M C D t e r m . F o r these transitions the M C D arises f r o m t h e B - t e r m as d e f i n e d b y Stephens transitions of electrons f r o m t h e t

lu

p r e d i c t e d to h a v e different signs.

a n d the t

(26), a n d

orbitals ( F i g u r e 2 ) are

2u

T h e i r experiments therefore

permit

i d e n t i f i c a t i o n of t h e e x c i t e d states f o r t w o of t h e charge transfer b a n d s w h i c h a r e i n t e r c h a n g e d f r o m t h e o r i g i n a l suggestion b y Jorgensen Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

D o r a i n , J o r d a n , a n d t h e i r students

(14).

at B r a n d e i s U n i v e r s i t y h a v e

r e c e n t l y r e p o r t e d some e x c i t i n g c r y s t a l spectra.

T h e y dissolved small

amounts of t h e hexahalo complexes as, f o r e x a m p l e , O s C l " , i n host 6

crystals s u c h as the P t C l

4

( I V ) , the Z n C L i ( I V ) , a n d t h e H f C l

2

4

( I V ) salts

of a l k a l i m e t a l ions ( 7 ) . T h e s e crystals w e r e c o o l e d t o l i q u i d h e l i u m t e m p e r a t u r e a n d t h e i r spectra w e r e r e c o r d e d w i t h h i g h - r e s o l u t i o n e q u i p ­ ment.

N o w , i n s t e a d of b r o a d b a n d s , t h e y o b s e r v e d t r e m e n d o u s

detail

i n t h e i r spectra. I n t h e r e g i o n f r o m 17,000-35,000 c m , w e l l i n excess of - 1

100 lines w e r e r e c o r d e d .

P o r t i o n s of t h e i r spectra i n v e r y n a r r o w regions

are s h o w n i n F i g u r e 13. T h e p o r t i o n of t h e s p e c t r u m i n t h e v i c i n i t y of 17,000 c m " corresponds 1

to t h e w e a k b a n d s h o w n i n F i g u r e 1. T h e

z e r o - z e r o l i n e is i d e n t i f i e d ( Β ) a n d is a p p a r e n t l y e x c i t e d b y q u a d r u p o l e excitation. M u c h stronger lines arise f r o m t h e v i b r o n i c e x c i t a t i o n o f t h e lines i n d i c a t e d v a n d v . T h e v a n d v represent the t w o t 4

3

4

lu

3

normal vibra­

tions of t h e o c t a h e d r a l i o n . F o r m a n y o f t h e b a n d s , t h e v i b r a t i o n a l A

Β

17000 17200 17400 17600

28800 29400 30000 30600

cm"'

Figure 13.

cm"

Spectra of the a ion, OsCl ~ 4

2

6

1

dissolved in host crystals

A. Host is KtPtCU. B. Host is CszZrCU. The Ο.Ό. scales are not equal in part A and B. Initial lines are enlarged by a factor of 5 in part B.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

96

PLATINUM GROUP METALS AND COMPOUNDS

progressions permit an identification of the symmetry of the excited state. This quality of spectrum also affords an incentive for the theorist to tackle the difficult problem of the spectral intensities. In the vicinity of 29,00030,000 cm" illustrated by the Β portion in Figure 13, the molar absorp­ tivity in solution is approximately 8000 cm" M" . However, from a con­ sideration of intensities, the ligandfieldparameters, which include the strong spin-orbit coupling and the vibrational frequencies, Jordan et al. (13) conclude that all the bands in the region up to at least 35,000 cm" are ligandfield—i.e.,d-d transitions. This, of course, challenges the conclusion mentioned earlier that these bands arose from charge transfer 7Γ —» t . Hence, some of the systematics of the band assignments need réévaluation. 1

1

1

1

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

2g

Summary The past two decades have witnessed a remarkable development in the experimental and theoretical considerations of the electronic absorption spectra of coordination complexes, of which the platinum metal compounds comprise an important segment. Despite their limited number of features, these spectra have proved useful for analytical purposes. With the development of ligandfieldtheory and molecular orbital treatment, they have provided rather considerable information about the energy states of complexes, the energies which can be associated with particular orbitals, and the trends that occur in these energies between various elements, with various ligands and environments. The development of these theories has in turn stimulated experimental investigations, so that polarization of absorption bands, the magnetic circular dichroism, low temperatures, and the utilization of crystalline environments have greatly extended possibilities for identification of the transitions. Most certainly, the next few years will see a further application of these techniques, a refinement of the methods and instrumentation,' and improved theoretical means for dealing with the problem of the energy states and the intensities.

Literature Cited (1) Anex, B. G., Ross, M. E., Hedgecock, M. W., J. Chem. Phys. 1967, 46, 1090. (2) Basch, H., Gray, H. B., Inorg. Chem. 1967, 6, 365. (3) Chatt, J., Gamlen, G. Α., Orgel, L. E.,J.Chem. Soc. (London) 1958, 486 (4) Cotton, F. Α., Harris, C. B., Inorg. Chem. 1967, 6, 369. (5) Day, P., Orchard, A. F., Thompson, A. J., Williams, R. J. P., J. Chem. Phys. 1965, 42, 1973. (6) Dickinson, R. G.,J.Am. Chem. Soc. 1922, 44, 2402. (7) Dorain, P. B., Patterson, Η. H., Jordan, P.C.,J.Chem. Phys. 1958, 49, 3845.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch007

7. MARTIN

Ultraviolet Spectroscopic Qualities

97

(8) Griffiths, J. Η. Ε., Owen, J., Ward, I. M., Proc. Roy. Soc. (London) 1953 A219, 526. (9) Harris, C. M., Livingstone, S. E., Stephenson, N. C.,J.Chem. Soc. (Lon­ don) 1958, 3697. (10) Henning, G. N., McCaffery, A. J., Schatz, P. N., Stephens, P. J.,J.Chem. Phys. 1968, 48, 5656. (11) Jacobson, Robert Α., Benson, James E., private communication. (12) Johannesen, R. B., Candela, G. Α., Inorg. Chem. 1963, 2, 67. (13) Jordan, P. C., Patterson, H. H., Dorain, P. B., J. Chem. Phys. 1968, 49, 3858. (14) Jorgensen, C. K., Acta Chem. Scand. 1956, 10, 500. (15) Jorgensen, C. K., Ibid., 1956, 10, 518. (16) Jorgensen, C. K., Ibid., 1963, 17, 1043. (17) Jorgensen, C. K., Mol. Phys. 1959, 2, 309. (18) Jorgensen, C. K., "Absorption Spectra and Chemical Bonding in Com­ plexes," Ch. 9, Pergamon, London, 1961. (19) Ref. 17, p. 114. (20) Martin, D. S., Jr., Tucker, Μ. Α., Kassman, A. J., Inorg. Chem. 1965, 4, 1682. (21) Mason, W. R., Gray, Η. B.,J.Am. Chem. Soc. 1968, 90, 5721. (22) McCaffery, A. J., Schatz, P. N., Lester, T. E., J. Chem. Phys. 1969, 50, 379 (23) McCaffery, A. J., Schatz, P. N., Stephens, P. J., J. Am. Chem. Soc. 1968, 90, 5730. (24) Miller, J. R., J. Chem. Soc. (London) 1965, 713. (25) Owen, J., Stevens, K. W. H., Nature 1953, 171, 836. (26) Stephens, P. J., Inorg. Chem. 1966, 5, 491. (27) Teggins, J. E., Gano, D. R., Tucker, Μ. Α., Martin, D. S., Jr., Ibid., 1967, 6, 69. RECEIVED December 16, 1969. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission, Contribution No. 2648.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8

N M R Spectra of Compounds of the Platinum G r o u p Metals

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

R. STUART TOBIAS Purdue University, Lafayette, Ind. 47907

Although resonances of the nuclei of platinum group metals have been observed in some cases, the small magnetic mo ments of many of these lead to very low NMR intensities and the large spins of many of the nuclei cause very broa signals. Of much more use to the chemist have been studi on H, F, and P resonances of ligands coordinated to the metals. Very highfieldresonances characterize hydride ligands. Since many compounds of these elements are ster eochemically rigid, nuclear magnetic resonance spectro­ scopy is helpful in the elucidation of their structures. A number of the organometallic derivatives are nonrigid, and NMR has been used to study their reactions. 1

19

31

'Tphe application of nuclear magnetic resonance to the study of the compounds of the platinum group metals has been limited by the properties of these nuclei. Data are collected in Table I for all of the isotopes of these elements which have nonzero spins. The only nuclei which have spins of 1/2 and which consequently give relatively high resolution spectra are Rh, Os, and Pt. All of the other isotopes have spins of 3/2 or greater and give very broad reso­ nances because of the nuclear quadrupole moment. Thesefinitequadrupole moments lead to rapid relaxation of the nuclei in environments not described by one of the cubic groups—i.e., when the coordination sphere has symmetry lower than T or O . As a result, spin-spin coupling usually is not observed with these nuclei. Of the three isotopes with spins of 1/2, Os occurs with very low natural abundance, 1.64%. This, combined with the very poor sensitivity of the nucleus compared to the proton, 7.93 Χ 10" at constant field, virtually precludes its study with contemporary spectrometers. Of all of these nuclei, only Rh and Pt lend themselves to NMR experiments. 103

d

187

195

h

187

5

103

195

98 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Table I.

Spectra

Natural Abundance j

Isotope

NMR Frequency 10 Kgauss Field, MHz

"Ru Ru Rh Pd 0s 189 191 193J 195

1.9 2.1 1.340 1.74 1.8 3.307 0.813 0.86 9.153

12.81 16.98 100. 22.23 1.64 16.1 38.5 61.5 33.7

1 0 1 1 0 3

1 0 5

1 8 7

0s

Ir

r

Pt

a

99

Compounds

Nuclear Properties of the Platinum Group Metals"

y

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

of

Sensitivity (Constant Field) Relative to !! = 1

%

Quadrupole Moment, e · 10~ Cm

Spin,

24

1

1.07 1.41 3.12 7.94 7.93 2.34 3.5 4.2 9.94

?

5/2 5/2 1/2 5/2 1/2 3/2 3/2 3/2 1/2

X 10X 10X 10X 10-" X 10-* X 10X 10X 10X 103 3

5

3

s

5

3

?

-

-

2.0 1.5 1.5

-

Reprinted from Ref. 57 by permission of Varian Associates.

O f the t w o ,

1 9 5

P t is s o m e w h a t easier to s t u d y b e c a u s e of its r e l a t i v e l y g o o d

sensitivity a n d h i g h resonance

frequency.

E v e n w i t h these l i m i t a t i o n s , n u c l e a r m a g n e t i c resonance has

made

significant c o n t r i b u t i o n s to f o u r areas of the c h e m i s t r y of the p l a t i n u m g r o u p m e t a l s : b o n d i n g p r o b l e m s , m o l e c u l a r stereochemistry,

solvation

a n d solvent effects, a n d d y n a m i c s y s t e m s — r e a c t i o n rates. S e l e c t e d e x a m ples i n e a c h of these areas are discussed i n t u r n . l i m i t a t i o n s , this r e v i e w is not m e a n t to be Bonding

B e c a u s e of

space

comprehensive.

Problems

C o n c e p t u a l l y , the simplest N M R e x p e r i m e n t i n v o l v e s the s t u d y of the resonance of the m e t a l n u c l e u s itself, y i e l d i n g c h e m i c a l shift values a n d i n some cases s p i n - s p i n c o u p l i n g constant d a t a . R e c e n t l y , the i n t e r n u c l e a r d o u b l e resonance t e c h n i q u e (17)

also has b e e n u s e d to m e a s u r e

these c h e m i c a l shifts. F i g u r e 1 shows c h e m i c a l shift d a t a for a series of square p l a n a r p l a t i n u m ( I I ) complexes

o b t a i n e d b y the I N D O R t e c h n i q u e (36).

The

p r o t o n resonance spectra of the l i g a n d s w e r e m o n i t o r e d w h i l e s w e e p i n g t h r o u g h the ical

shifts,

1 9 5

almost

[(MeO) P] Pt 3

P t resonant f r e q u e n c y range.

4

2 +

1700

(high

ppm

field)

from

T h e l a r g e range of

(Me S) PtCl 2

2

2

(low

chem-

field)

to

suggests t h a t the shifts are d o m i n a t e d b y

the p a r a m a g n e t i c c o n t r i b u t i o n . Q u a l i t a t i v e l y , this is s u p p o r t e d b y

the

o b s e r v a t i o n that the complexes h a v i n g l o w field resonances a b s o r b i n the b l u e r e g i o n of the s p e c t r u m , w h i l e those w i t h the highest field resonances are colorless. P i d c o c k , R i c h a r d s , a n d V e n a n z i (47) investigations of

1 9 5

have conducted more detailed

P t c h e m i c a l shifts b y d i r e c t m e a s u r e m e n t of the p l a t i -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

100

PLATINUM

GROUP

METALS

AND

COMPOUNDS

High R e l d +2 {[(MeO) P] Pt) 3

1500

4

trans(Et P) PtHCI 3

2

^cis(Et P)^tCI 3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

1000

2

cis(Et2PhP) PtCI 2

^^ci<(EtO) P] PtCI 3

2

2

2

ppm

I

^trans(Et PhP) PtCl 2

2

2

500 ^Mrans(Et P) PtCI 3

^

2

. cis(Et S)pPtCI 2

\ *

2

cis(Me S^PtCI 2

2

cis(Et Se^PtCI 2

2

2

trans(Et Se)PtCI

OL

2

2

^ - -t r a n s ( E t S ) P t C I Low Field * N t r a n s ( M e S ) P t C I 2

2

2

2

2

2

Chemical Communications

Figure

1.

n u m resonances.

Chemical shifts in phtinum(II) redrawn from Ref. 36

complexes;

T h e c o m p o u n d trans- [ P t C l p e p y ] , p e p y = 2

4-pentyl-

2

p y r i d i n e , w a s u s e d as the reference. T h e g e n e r a l E x p r e s s i o n 1 for n u c l e a r s h i e l d i n g , σ, g i v e n b y R a m s e y (50)

was s i m p l i f i e d u s i n g a p r o c e d u r e first

e m p l o y e d b y G r i f f i t h a n d O r g e l (22) σ =

-

2 β Σ (E njé 0 2

+

n

-

[<ψ |Σ Ζ |ψ»><ψ»|Σ Z r - | ψ >

E )~ 0

to d e s c r i b e the shifts of c o b a l t ( I I I )

l

0

<β

fcz

i

<φ |Σ Ζ 0

k

λ 2

Γ - |φ Χψ |Σ λ

3

η

fc

3

0

k

η

Ζ -,|φ >] β

i

(1)

β

complexes. I n E q u a t i o n 1, ψ a n d ψ are the w a v e f u n c t i o n s of the g r o u n d a n d e x c i t e d states, E a n d E are the c o r r e s p o n d i n g energies, l is the ζ 0

0

n

η

ie

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR Spectra

of

101

Compounds

c o m p o n e n t of the a n g u l a r m o m e n t u m operator f o r t h e f t h e l e c t r o n , r is t

the distance of the i t h e l e c t r o n f r o m t h e n u c l e u s , a n d β is t h e B o h r m a g n e t o n . W i t h P t ( I I ) complexes, t h e g r o u n d state is a singlet. I f i t is a s s u m e d t h a t a l l of t h e complexes c a n b e d e s c r i b e d i n terms of m e t r y , o n l y singlet A

2g

and E

sym­

e x c i t e d states n e e d b e c o n s i d e r e d , since

g

these are the s y m m e t r y species of t h e a n g u l a r m o m e n t u m u n d e r t h e operations of the

components

p o i n t g r o u p . T h i s leads to t h e s i m p l i f i e d

E x p r e s s i o n 2 f o r t h e resonant f r e q u e n c y , v. H e r e , Η is the m a g n e t i c

field

strength, A is t h e d i a m a g n e t i c s h i e l d i n g c o n t r i b u t i o n , a n d Β contains ν = 2

ι

l

λβ

as w e l l as p h y s i c a l constants.

C (r~ ) M

- > iA,„ + BH\ A —>

AH + 2ΒΗ\ Α

3

%

lg

T h e term C

M

(2)

is t h e m o l e c u l a r

o r b i t a l m i x i n g coefficient f o r t h e p l a t i n u m 5d o r b i t a l , a n d t h e r " a v e r a g e Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

3

is t a k e n over the p l a t i n u m d r a d i a l f u n c t i o n . T h e differences i n e n e r g y of t h e g r o u n d a n d first e x c i t e d A

a n d E states are g i v e n i n terms of t h e

2g

g

t r a n s i t i o n w a v e l e n g t h s , λ. I f this s i m p l e m o d e l

is a d e q u a t e

to represent

the shielding i n

these p l a t i n u m ( I I ) complexes, a p l o t of (v — v f ) vs. (2k A 1

re

X*Ai0 -> E ) 1

g

lg

-» A 1

2g

+

s h o u l d b e linear. A l t h o u g h a v e r y r o u g h l i n e a r r e l a t i o n is

o b s e r v e d for complexes of t h e t y p e P t X L , X = 2

h a l i d e , w h e n X is c o n ­

2

stant a n d L is v a r i e d , different f a m i l i e s of curves w e r e o b t a i n e d as X w a s v a r i e d f r o m C I " to B r " to Γ .

I t seems l i k e l y t h a t m o r e

electronegative

ligands—e.g., C I " — l e a d to a c o n t r a c t i o n of the p l a t i n u m 5d orbitals a n d a n increase i n the Β p a r a m e t e r t h r o u g h its r " d e p e n d e n c e . 3

D e a n a n d G r e e n (14)

also h a v e o b t a i n e d

1 9 5

P t c h e m i c a l shifts f r o m

d o u b l e resonance studies of t h e s q u a r e p l a n a r h y d r i d e s L =

[Pt(PEt ) HL], 3

2

N O 3 - , N 0 " , C I " , B r " , Γ , S C N " , C N , a n d benzoate. T h e y f o u n d l i t t l e 2

c o r r e l a t i o n b e t w e e n t h e o p t i c a l properties—i.e., the s p e c t r o c h e m i c a l se­ r i e s — a n d t h e sequence of c h e m i c a l shifts a n d c o n c l u d e d that t h e e x c i t a ­ t i o n energies d i d n o t d o m i n a t e t h e p a r a m a g n e t i c s c r e e n i n g t e r m . T h e shifts i n c r e a s e d i n t h e o r d e r N 0 " < 3

CN~ <

N0 "< 2

CI" <

—S C N

< Br" <

Γ . T h i s o r d e r is s i m i l a r to t h e n e p h e l a u x e t i c series, a n d D e a n

a n d G r e e n suggested that changes i n the m o l e c u l a r o r b i t a l m i x i n g co­ efficients w e r e m a i n l y r e s p o n s i b l e f o r t h e shifts. I n p r a c t i c e , i t is n o t possible to separate the effect of changes i n the M O m i x i n g coefficients f r o m those of o r b i t a l e x p a n s i o n a n d c o n t r a c ­ t i o n , since t h e y c o n t r i b u t e to t h e same C (r~ ) 2

M

3

term. Pidcock, Richards,

a n d V e n a n z i chose to a t t r i b u t e t h e discrepancies to o r b i t a l c o n t r a c t i o n w h i l e D e a n a n d G r e e n c o n s i d e r e d o n l y changes i n the m i x i n g coefficient. It seems c e r t a i n that t h e large c h e m i c a l shifts o b s e r v e d f o r these d i v a l e n t p l a t i n u m complexes arise m a i n l y f r o m the p a r a m a g n e t i c terms, b u t t h e simplified models used have been inadequate for a quantitative descrip­ t i o n of the s h i e l d i n g .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

102

PLATINUM

GROUP

METALS

AND

COMPOUNDS

C o n s i d e r a b l y m o r e i n f o r m a t i o n o n the n a t u r e of the b o n d i n g i n these complexes has b e e n o b t a i n e d f r o m measurements of the s p i n - s p i n c o u ­ p l i n g of

1 0 3

R h and more frequently

A u s e f u l r e v i e w (40)

1 9 5

P t to

H and

1

3 1

P nuclei i n ligands.

of s p i n - s p i n c o u p l i n g b e t w e e n d i r e c t l y b o n d e d

atoms i n c l u d i n g these has a p p e a r e d r e c e n t l y . P h o s p h o r u s - 3 1 s p e c t r a h a v e y i e l d e d a w e a l t h o f d a t a o n cis ( I I ) num (II)

complexes w h e r e X =

M c F a r l a n e (24) 6

5

3

w

(46,

2

2

C H , C H , C H , and C H ; G r i m and 3

2

5

3

7

P(C H )3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

4

4

P(C H9)

9

4

X— P t - X I P(C H9)3

9

3

(C4H9LP-Pt-x I X

4

I F e r e n c e (23)

isomers of p l a t i ­ G r i m , Keiter, and

48).

h a v e o b t a i n e d s i m i l a r data for isomers of the complexes

(R (C H ) - P) PtCl , R = n

a n d trans ( I )

halide

Π

h a v e r e p o r t e d c o u p l i n g constants for cis a n d trans isomers

of R h ( I I I ) complexes. D a t a for a n u m b e r of p l a t i n u m ( I I ) p h o s p h i n e complexes are t a b u ­ l a t e d i n T a b l e I I . T h e c o u p l i n g constant for the cis i s o m e r is ca. 1.5 times that for the trans isomer. Table II.

Platinum-19 5—Phosphorus-31 Spin—Spin Coupling Constants in Platinum (II) Complexes j(i95

Compound

cis Isomer

0

PtCl (Bu P) PtBr (Bu P) PtI (Bu P) PtCl (Et P) PtCl (Pr P) PtCl (Bu P) PtCl (Et PhP) PtCl (Pr PhP) PtCl (Bu PhP) PtCl (BuPh P) 2

3

2

2

3

2

2

2

3

2

2

3

2

2

3

2

2

2

2

2

2

2

2

2

* Bu

2

2

=

2 2

W - C 4 H 9 , Pr

=

71-C3H7, E t

Hz.

trans Isomer 2380 ± 2334 ± 2200 ± 2400 2385 2392 2482 2463 2462 2531

3508 ± 6 3479 db 10 3372 ± 3520 3530 3500 3530 3561 3551 3641

2

3

pt-tip),

=

C 2 H 5 , Ph

=

J /Ji,

Ref.

1.47 1.49 1.53 1.47 1.48 1.46 1.42 1.45 1.44 1.44

U6) (46) U6)

cis

4 8 4

m)

m (Π) (Π)

m) (H)

C H . 6

5

C o n s e q u e n t l y , a d e t e r m i n a t i o n of / is sufficient for a s t r u c t u r e as­ s i g n m e n t . I n t h e i r o r i g i n a l note, P i d c o c k et al. suggested that J

cis

> /trans

w a s c a u s e d b y changes i n σ b o n d i n g r e s u l t i n g f r o m the s y n e r g i c effect of 7Γ b a c k b o n d i n g b e t w e e n p l a t i n u m a n d p h o s p h o r u s . I n 1966, t h e y u s e d t h e P o p l e - S a n t r y (49)

E q u a t i o n , 3, for t h e F e r m i c o n t a c t t e r m i n t h e ex-

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

103

Compounds

p r e s s i o n for s p i n - s p i n c o u p l i n g a n d c o n c l u d e d t h a t the difference

was

c a u s e d b y s e c o n d a r y σ o r b i t a l r e h y b r i d i z a t i o n effects r a t h e r t h a n as a c o n s e q u e n c e of π b o n d i n g J cc

effects. 2

2

Μ

(3)

ψ^(0) 1 1 ψχ(0)

ΑΕ-ΐα *χ 1

ΎΜΎχ

2

T h e F e r m i c o n t a c t t e r m seems to d o m i n a t e t h e d i r e c t c o u p l i n g b e ­ t w e e n the h e a v y metals a n d l i g a n d d o n o r atoms. I n E q u a t i o n 3, t h e y s a r e t h e n u c l e a r m a g n e t o g y r i c r a t i o s , Δ Ε is a n a v e r a g e s i n g l e t - t r i p l e t ex­ c i t a t i o n energy, «

M

and «

are the m i x i n g coefficients for the m e t a l v a l ­

x

ence s o r b i t a l a n d l i g a n d v a l e n c e s o r b i t a l i n t h e h y b r i d o r b i t a l s u s e d to d e s c r i b e the M - X b o n d , a n d ^ M ( O )

2

and ψ ( 0 ) χ

2

are the e l e c t r o n densities

at t h e M a n d X n u c l e i , r e s p e c t i v e l y . F o r c o u p l i n g b e t w e e n

3 1

P and

1 9 5

Pt

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

i n t h e cis a n d trans isomers, the γ s are u n c h a n g e d ; a n d to a first a p p r o x i ­ m a t i o n , i t m a y be a s s u m e d t h a t Δ Ε is constant. O r b i t a l c o n t r a c t i o n effects are n e g l e c t e d ; i.e., ψν(0)

a n d ψ χ ( 0 ) are a s s u m e d to b e the same i n the

t w o isomers. T h e c h a n g e f r o m cis to trans i s o m e r s h o u l d n o t h a v e a n y significant effect o n the p h o s p h o r u s o r b i t a l f o r the b o n d i n g p a i r . q u e n t l y , to a first a p p r o x i m a t i o n , /

oc

a M

2

;

Conse­

i-e., the c o u p l i n g constant is

p r o p o r t i o n a l to the s c h a r a c t e r of the p l a t i n u m h y b r i d u s e d to b i n d the phosphine. T h e s p i n - s p i n c o u p l i n g d a t a i n d i c a t e t h a t the p l a t i n u m s c h a r a c t e r tends to b e c o n c e n t r a t e d i n the b o n d s to the m o r e p o l a r i z a b l e p h o s p h i n e ligands.

P i d c o c k et al. (46)

a d o p t e d the t e r m "trans i n f l u e n c e " to

de­

s c r i b e the trans b o n d w e a k e n i n g effect o b s e r v e d w i t h l i g a n d s s u c h as p h o s p h i n e s . I n the cis c o m p l e x , the m e t a l d a n d s c h a r a c t e r c a n b e m a x i ­ m i z e d i n t h e b o n d s to t h e t w o p h o s p h i n e s , l e a v i n g the trans b o n d s w i t h p r e d o m i n a n t l y 6p c h a r a c t e r consistent w i t h t h e i r ease of s u b s t i t u t i o n a n d l o n g b o n d lengths

(56).

S i m i l a r m e a s u r e m e n t s of t h e plexes of p l a t i n u m a l k y l s (1)

1 9 5

Pt-

3 1

P coupling in phosphine

com­

a g a i n i n d i c a t e that the s c h a r a c t e r tends to

concentrate i n the b o n d s to t h e m o s t p o l a r i z a b l e l i g a n d s , the a l k y l g r o u p s . Structures I I I (24),

IV (I),

and V

(1)

s h o w the effect of i n c r e a s i n g

m e t h y l a t i o n of P t C l [ P ( C H ) ] . T h e b o n d to a l i g a n d trans to a m e t h y l 2

J = 3520 Hz.

2

5

3

2

J=4179 Hz.

J = 1 8 5 6 Hz.

J = 1719 Hz.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

104

PLATINUM

GROUP

METALS

AND

COMPOUNDS

g r o u p is w e a k e n e d , consistent w i t h a c o n c e n t r a t i o n of the p l a t i n u m 6p c h a r a c t e r i n these bonds. S i m i l a r effects h a v e b e e n r e p o r t e d for a r y l , s i l y l , a n d g e r m y l d e r i v a t i v e s of p l a t i n u m ( I I )

(25).

I n g e n e r a l , the /

1 9 5

Pt-

3 1

P

values are s m a l l w h e n p h o s p h o r u s is trans to a l i g a n d of h i g h trans i n ­ fluence—e.g.,

a p h o s p h i n e or a c a r b a n i o n — a n d l a r g e w h e n trans to a

relatively nonpolarizable ligand like chloride. S i m i l a r effects are o b s e r v e d w i t h o c t a h e d r a l complexes w h e r e J

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

1.5 /trans as i l l u s t r a t e d i n structures V I a n d V I I (46).

«

c i B

T h e r a t i o of the

-m

S I c o u p l i n g constants for P t ( I V ) : P t ( I I ) =

0.59 for the cis complexes

II

a n d V I I a n d 0.61 f o r the trans complexes I a n d V I . T h e fact t h a t these values are near t h a t of the r a t i o of s c h a r a c t e r for d sp 2

1/6:1/4 =

a n d dsp

s

hybrids,

1

0.67, suggests t h a t |^ (0)| is c o m p a r a b l e f o r b o t h o x i d a t i o n Pt

2

states. T h e s i m i l a r i t y of the b e h a v i o r of P t ( I I ) a n d P t ( I V ) complexes

was

u s e d b y P i d c o c k et al. as e v i d e n c e t h a t o n l y σ b o n d i n g effects w e r e r e ­ s p o n s i b l e for the cis—trans difference.

I t is g e n e r a l l y a s s u m e d t h a t (Ln—dv

b a c k b o n d i n g is n e g l i g i b l e w i t h P t ( I V ) , b u t this is b a s e d o n P t ( I V )

d

o r b i t a l s b e i n g c o n t r a c t e d w i t h respect to P t ( I I ) o r b i t a l s . T h e

evidence

also c i t e d f o r the i n v a r i a n c e of |^pt(0)|

suggests

2

w i t h o x i d a t i o n state

that άττ-άττ b a c k b o n d i n g s h o u l d b e c o m p a r a b l e i n P t ( I I )

and P t ( I V )

complexes. P a r s h a l l (44, s p e c t r a of the

45)

has u s e d

fluorophenyl

fluorine-19

nuclear magnetic

to s t u d y t h e trans influence of the X l i g a n d . T h e m e t a

F

P(C

resonance

d e r i v a t i v e s of p l a t i n u m ( I I ) , V I I I a n d I X ,

2

H

5

)3

PCC H ) 2

p a r a m e t e r varies w i t h the σ d o n o r c h a r a c t e r of the

5

1 9

F shielding

3

fluorophenyl

ring

substituent, w h i l e the p a r a s h i e l d i n g p a r a m e t e r is affected m a r k e d l y b y

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

105

Compounds

the 7Γ d o n o r character of the substituent. C o n s e q u e n t l y , the p a r a s h i e l d ­ i n g p a r a m e t e r reflects the a b i l i t y of the l i g a n d X b o u n d to p l a t i n u m to c o m p e t e w i t h the p - f l u o r o p h e n y l g r o u p f o r p l a t i n u m d* e l e c t r o n d e n s i t y . T o correct for s i m p l e i n d u c t i v e effects, the difference b e t w e e n the p a r a a n d the m e t a s h i e l d i n g parameters w a s c o n s i d e r e d .

I n this w a y ,

the

l i g a n d s X w e r e classified i n i n c r e a s i n g o r d e r of -π acceptor c h a r a c t e r as CI" ^ C H 6

Γ < —

5

Br" <

p-FC H 6

O C N - or N C O " ^ ^

4

m-FC H 6

<

4

CH

3

SnCl - ^

<

- S C N ' or - N C S "

<

C H — C ^ C < CN".

3

6

5

T h e r e h a v e b e e n some d e t e r m i n a t i o n s of the signs of t h e s p i n - s p i n c o u p l i n g constants for complexes of p l a t i n u m . A s m i g h t b e e x p e c t e d , the c o u p l i n g constants in [ ( C H ) P t C l ] 2

5

3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

respectively. trans

2

/(

4

1 9 5

P t - C H ) and / (

(32),

3

2

1 9 5

P t - C H ) h a v e o p p o s i t e signs 3

a n d the absolute values are 86 a n d 72.0 H z ,

H e t e r o n u c l e a r d o u b l e resonance measurements o n cis a n d

dichlorobis(triethylphosphine)platinum(II)

i7(i95 _3ip) Pt

positive. (PEt ) 3

2

p

i s

0 s i t i v

e

2jr(3ip_

5

C H 2

)

(39)

negative, and / ( 3

i s

S i m i l a r l y , h e t e r o n u c l e a r d o u b l e resonance (35)

sign, w h i l e / ( 2

show that 7 ( 3 1

1 9 5

Pt-

3 1

P)

and V (

1 9 B

indicate 1 9 5

that

P t - C H ) is 2

spectra of

PtHCl-

P M H ) are of t h e same

Ρ - Ή ) is of opposite sign.

Stereochemistry T h e p r i n c i p a l a p p l i c a t i o n of N M B w i t h c o m p o u n d s of the p l a t i n u m g r o u p metals has b e e n i n the s t u d y of t h e i r stereochemistry. trans isomers of the P t ( P B ) L 3

2

2

Cis and

a n d P t ( P B ) X 4 t y p e are i d e n t i f i e d easily 3

2

because of the difference i n the c o u p l i n g constants as d i s c u s s e d above. T h e tris ( t r i - n - b u t y l ) p h o s p h i n e c o m p l e x of r h o d i u m t r i c h l o r i d e has the trans ( m e r ) s t r u c t u r e X (23).

Two

3 1

P resonances are o b s e r v e d w i t h

CI

I

^ci

Ç(C Hg)3 4

X a n i n t e n s i t y ratio of 2 : 1 . B o t h signals are s p l i t i n t o doublets b y c o u p l i n g with

1 0 3

Bh, /(

1 0 3

Bh-

3 1

P ) a

—

114, / (

1 0 3

Bh-

3 1

P ) 6

— 84 H z .

A g a i n the

r a t i o of c o u p l i n g constants for p h o s p h o r u s trans to c h l o r i n e r e l a t i v e to p h o s p h o r u s trans to p h o s p h i n e is ca. 1.5 T h i s s p e c t r u m also exhibits s m a l l splittings of the m o r e intense p h o s p h o r u s resonance b y 21 H z c a u s e d b y c o u p l i n g t h r o u g h t w o b o n d s w i t h the u n i q u e p h o s p h o r u s - 3 1 n u c l e u s P . a

T h e s p l i t t i n g of the less intense resonance b y the t w o e q u i v a l e n t p h o s ­ phorus n u c l e i was not resolved.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

106

PLATINUM

GROUP

METALS

AND

COMPOUNDS

P h o s p h o r u s - 3 1 p r o t o n s p i n - s p i n c o u p l i n g constants d e t e r m i n e d w i t h p r o t o n resonance

spectra h a v e b e e n u s e d to d i s t i n g u i s h cis a n d trans

isomers of h y d r i d o complexes c o n t a i n i n g p h o s p h i n e l i g a n d s . F o r e x a m p l e , t h e complexes I r H a . Y 3 . J L 3 ( Y is a u n i n e g a t i v e a n i o n , L is a n e u t r a l p h o s ­ phine ligand) have / ( 2

3 1

P-H) =

trans H a n d L l i g a n d s ( 6 ) .

1 1 - 2 1 H z for cis a n d 1 3 0 - 1 6 3 H z for

A n a l o g o u s d a t a h a v e b e e n u s e d to assign

s t r u c t u r e X I to the p r o d u c t of the r e a c t i o n b e t w e e n R h C l ( P P h ) 3

H C 1 i n s o l u t i o n (2).

3

and

T h e h y d r i d e resonance gives a p a i r of o v e r l a p p i n g

triplets c e n t e r e d at τ =

26.1 p p m because of c o u p l i n g w i t h the r h o d i u m Η ( C

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

( C

4

H

H

9

)

)

4 9 3

3

P \

P

^ ( S )

I

C l

I CI

ZI n u c l e u s a n d t w o e q u i v a l e n t p h o s p h o r u s n u c l e i . T h e assignment of the h y d r i d e cis to the p h o s p h i n e s is b a s e d o n the s m a l l v a l u e of =

2

/(

3 1

Ρ-Ή)

17 H z . M o r g a n , R e n n i c k , a n d S o o n g (41)

used coupling between platinum-

195 a n d the h y d r o x y l i c protons of [ ( Ο Η ) Ρ ί Ο Η ] , 3

3

4

X I I , to s h o w that the

2 H h y d r o x i d e was i s o s t r u c t u r a l w i t h the c h l o r i d e , b r o m i d e , a n d i o d i d e . p l a t i n u m is 3 3 . 7 %

1 9 5

Since

P t , w h i l e a l l other n a t u r a l l y - o c c u r r i n g isotopes h a v e

zero s p i n , a g i v e n h y d r o x o g r o u p b r i d g e s b e t w e e n 3 p l a t i n u m s w h e r e 1, 2, or a l l 3 m a y h a v e spins of 1/2.

T h e p r e d i c t e d p r o t o n resonance spec­

t r u m f o r cage s t r u c t u r e X I I is i l l u s t r a t e d i n F i g u r e 2, a n d this agrees w i t h the o b s e r v e d s p e c t r u m w h e n / ( 2

1 9 5

Pt-OH) =

11.3 H z , τ == ca. 11.5 p p m .

T h e m a g n i t u d e of c o u p l i n g b e t w e e n the m e t h y l protons a n d p l a t i ­ n u m - 1 9 5 also is h e l p f u l i n a s s i g n i n g structures to t r i m e t h y l p l a t i n u m ( I V ) complexes.

The

2

/(

1 9 5

P t — C H ) c o u p l i n g constant appears to b e 3

influ­

e n c e d p r i m a r i l y b y the n a t u r e of the l i g a n d trans to t h e m e t h y l g r o u p , a n d the solvent u s e d makes little difference

(33,

54).

T h i s same effect

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra of

107

Compounds

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

H

1 x(0.662)

J

3x(0.662 x 2

ι

I

ι

0.337)

3x(0.662x0.337 ) 2

1X(0.337)

3

Inorganic Chemistry

Figure 2. resonance

Predicted spectrum for the hydroxylic proton of [(CH^sPtOH]^; observed spectrum re­ drawn from Ref. 41

has b e e n o b s e r v e d for s p e c t r a of the c o m p l e x cations PY3-w]

+

(py =

[(ΟΗ ) Ρί(ΟΗ ),ι3

3

2

p y r i d i n e ) d e t e r m i n e d w i t h aqueous solutions ( 7 ) .

Only

t w o c o u p l i n g constants w e r e o b s e r v e d f o r m i x t u r e s of these c o m p l e x e s w i t h values of 79.7 H z f o r m e t h y l s trans to w a t e r m o l e c u l e s a n d 67.7 H z f o r m e t h y l s trans to p y r i d i n e . values f o r t h e / ( 2

1 9 5

S t r u c t u r e s X I I I to X I X i l l u s t r a t e average

P t - C H ) c o u p l i n g constants as the l i g a n d trans t o t h e 3

m e t h y l g r o u p s are v a r i e d ( 3 3 ) .

Pt—CI ~ΧΊΤΤ

CI

J

l 9 5

P t - H = 81.7

•Pt

Br SET

Ο

80.1

79.1 H z .

Pt—ο !

j195 1 R

H =

Ζ2Ε

7 8 β 0

Ρί^—Ο

Br

/

•Pi—

sznr

c

Ν

75.9

74.9 Hz.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

108

PLATINUM

j195 ] P t

H

GROUP

METALS

AND

COMPOUNDS

= 74.1Hz.

O n e a p p l i c a t i o n of these d a t a is i l l u s t r a t e d i n X X . T r i m e t h y l p l a t i n u m ( I V ) oxinate is d i m e r i c . T h e m o l e c u l e has a t w o - f o l d axis i n s o l u ­ t i o n , a n d three m e t h y l p r o t o n resonances w i t h c o u p l i n g constants of 80.4,

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

76.0, a n d 70.3 H z are o b s e r v e d .

T h e s i g n a l w i t h the smallest J is assigned

X X to t h e m e t h y l protons trans to n i t r o g e n a n d the o t h e r t w o signals to m e t h y l s trans to oxygen.

T h e s p e c t r u m shows t h a t the b o n d s f r o m P t to

the t w o b r i d g i n g oxygens are not e q u i v a l e n t . T h e c r y s t a l l o g r a p h i c values w e r e 2.22 ± 0.03 a n d 2.29 ± 0.04 A , a n d the errors i n the l i g h t a t o m

(34)

positions w e r e sufficiently l a r g e to leave the n o n e q u i v a l e n c e of the b r i d g e bonds i n doubt. Structures c a n b e assigned to square p l a n a r complexes P d X ( P R ) 2 and P t X ( P R ) 2

2

3

3

2

(X =

of the t y p e

u n i n e g a t i v e a n i o n ) o n the basis of

p r o t o n r a t h e r t h a n p h o s p h o r u s - 3 1 resonance

by using dimethylphenyl-

p h o s p h i n e as the l i g a n d (27,29).

T h e free l i g a n d shows a d o u b l e t m e t h y l

p r o t o n resonance, τ =

2

8.61 p p m , / (

3 1

Ρ-Ή) =

1.7 H z , because of c o u ­

p l i n g w i t h the p h o s p h o r u s n u c l e u s . I n the cis complexes, a s h a r p d o u b l e t also is o b s e r v e d / ( 2

3 1

Ρ - Ή ) = 7 to 13 H z . I f the t w o d i m e t h y l p h e n y l p h o s -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

109

Compounds

p h i n e s are m u t u a l l y trans, the resonance is u s u a l l y a w e l l r e s o l v e d t r i p l e t b e c a u s e of c o u p l i n g of the m e t h y l protons w i t h b o t h of the p h o s p h o r u s n u c l e i . T h e s e complexes are best t r e a t e d as A A ' X X ' systems ( 3 9 ) 3

very small

3 1

P....

the trans i s o m e r J (

with

3

P c o u p l i n g constants i n the cis isomers, w h i l e for

3 1

3 1

P ...

3 1

P) > >

10 H z . C o n s e q u e n t l y , d e t e r m i n a t i o n

of the P M R s p e c t r u m suffices for the s t r u c t u r e assignment. c o u p l i n g s c h e m e has b e e n o b s e r v e d

A

similar

for o c t a h e d r a l i r i d i u m ( I I I )

com-

p o u n d s of the t y p e [ I r X Y ( P M e P h ) ] ( X a n d Y are u n i n e g a t i v e a n i o n s ) 2

2

3

(28). P r o t o n N M R has b e e n u s e d to s t u d y the g e o m e t r i c a l isomers of the 2,5-dithiahexane complexes [RhCl L ] 2

2

+

of R h C l

3

i n D 0 s o l u t i o n . C a t i o n i c species 2

are o b t a i n e d , a n d the trans a r r a n g e m e n t of c h l o r i d e s

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

assigned o n the basis of v i b r a t i o n a l spectra (58).

was

B e c a u s e of t h e possible

d i t h i a h e x a n e l i g a n d c o n f o r m a t i o n s , u p to five different isomers c a n exist w i t h trans c h l o r i d e s . doublets w i t h 1 0 3

3

/(

1 0 3

T h e p r o t o n resonance s p e c t r u m shows a series of

Rh- H) 1

=

1.05 H z .

B y i r r a d i a t i o n at t h e

proper

R h resonance f r e q u e n c y , the doublets c a n b e c o l l a p s e d one b y

g i v i n g the

1 0 3

R h c h e m i c a l shifts i n the different complexes

different species w e r e i d e n t i f i e d w i t h

1 0 3

(38).

one,

Seven

R h c h e m i c a l shifts over the r a n g e

0 - 2 9 6 p p m , i n d i c a t i n g t h a t some cis isomers also w e r e present. S t r u c t u r e X X I was assigned to the i s o m e r w i t h a shift of 38 p p m r e l a t i v e to t h e lowest

field

resonance,

m e t h y l resonances

because the s p e c t r u m

showed

three

different

w i t h one t w i c e the i n t e n s i t y of the other t w o , c o n -

sistent w i t h this geometry.

XXI

Solvation and Solvent Effects S o m e studies u s i n g oxygen-17 N M R spectroscopy w i t h aqueous ions.

solutions of p l a t i n u m ( I I )

have been

and organoplatinum ( I V )

M a n y years ago, it was r e p o r t e d t h a t treatment of

w i t h a n aqueous s o l u t i o n of A g N 0

3

or A g S 0 2

4

made cat-

PtCl (NH ) 2

2

2

gave c o n c e n t r a t e d s o l u -

tions of a species p r e s u m e d to b e the d i a q u o d i a m m i n e p l a t i n u m ( I I ) c a t i o n Solutions of the p e r c h l o r a t e salt s h o w a b o u n d w a t e r

oxygen-17

resonance s i g n a l 92.6 =t 1 p p m u p f i e l d f r o m the b u l k w a t e r

resonance

(30). (20).

T h i s l a r g e c h e m i c a l shift for the w a t e r b o u n d to p l a t i n u m m a y b e

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

110

PLATINUM

GROUP

METALS

AND

c o m p a r e d w i t h t h e v a l u e of ca. —11 p p m for A 1 ( C 1 0 ) 4

COMPOUNDS

solutions

3

(9).

T h e r e w a s n o c h a n g e i n the c h e m i c a l shift over the t e m p e r a t u r e r a n g e 29° to 8 5 ° , i n d i c a t i n g that the w a t e r is r e l a t i v e l y i n e r t to s u b s t i t u t i o n . I n t e g r a t i o n of the b o u n d a n d b u l k w a t e r resonances gave the h y d r a t i o n number

as 1.9

±

[(H N)2Pt(OH )2] 3

2

0.1, c o n f i r m i n g the f o r m u l a t i o n of 2 +

.

the

cation

as

U n d o u b t e d l y , this c a t i o n is sufficiently i n e r t t h a t

the s o l v a t i o n n u m b e r c o u l d be d e t e r m i n e d b y conventional—e.g.,

isotope

dilution—techniques. T h e h y d r a t i o n of the t r i m e t h y l p l a t i n u m c a t i o n also has b e e n s t u d i e d by

1 7

0 N M R of aqueous solutions of ( C H ) P t C 1 0 3

3

4

Although

(20, 21).

m a n y p l a t i n u m ( I V ) complexes are n u m b e r e d a m o n g the most i n e r t co­ o r d i n a t i o n c o m p o u n d s k n o w n , the w a t e r molepules b o u n d to ( C H ) P t 3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

exchange r a p i d l y w i t h the b u l k solvent at r o o m t e m p e r a t u r e . 0 ° C is i t possible to r e c o r d a b o u n d w a t e r resonance.

3

+

O n l y near

E m p l o y i n g the

m o l a l shift of the b u l k w a t e r solvent c a u s e d b y a d d e d D y ( C 1 0 ) , i t w a s 4

possible to d e t e r m i n e the h y d r a t i o n n u m b e r to b e 3.0 ±

is f o r m u l a t e d c o r r e c t l y as o c t a h e d r a l [ ( C H ) P t ( O H ) ] . 3

the l a r g e q u a d r u p o l e m o m e n t of the w i t h the

1 9 5

3

0 nucleus, 1 =

1 7

2

3

0.1. T h e c a t i o n 3

Because

+

of

5/2, no coupling

P t n u c l e u s w a s detected i n a n y of the spectra d e s c r i b e d above.

T h e s e experiments i l l u s t r a t e the v e r y great l a b i l i t y of some of the organo d e r i v a t i v e s of the p l a t i n u m g r o u p metals. C l e g g and H a l l (8)

n o t e d that the a d d i t i o n of s u l f u r i c a c i d to a n

aqueous s o l u t i o n of [ ( C H ) P t ( N H ) ] C l caused a shift of 0.5 p p m i n 3

3

3

3

the m e t h y l p r o t o n resonance a n d a n increase i n the v a l u e of / ( 2

1 9 5

Pt-CH ) 3

f r o m 71.0 to 79.7 H z because of r a p i d f o r m a t i o n of the t r i a q u o species. A d d i t i o n of a n excess of the l i g a n d s H C N H , p y r i d i n e , S C N " , N 0 " , a n d 3

2

C N " a l l gave rise to spectra c h a r a c t e r i s t i c of the c o m p l e x e d platinum ( I V ) cation

2

trimethyl­

(7).

S a w y e r a n d c o w o r k e r s have s t u d i e d the p r o t o n resonance s p e c t r a of aqueous solutions of the 1:1 a n d 1:2 complexes f o r m e d f r o m P t ( I I ) Pd(II)

(53),

and Rh(III)

(52)

(51),

w i t h nitrilotriacetic acid, N - m e t h y l -

i m i n o d i a c e t i c a c i d , a n d i m i n o d i a c e t i c a c i d as a f u n c t i o n b o t h of

tem­

p e r a t u r e a n d of p H . T h e acetate m e t h y l e n e protons e x h i b i t a n A B p a t ­ t e r n i n a l l of the complexes, i n d i c a t i n g that the lifetimes of m e t a l - o x y g e n a n d m e t a l - n i t r o g e n b o n d s are r e l a t i v e l y long—i.e., that the

complexes

are s t e r e o c h e m i c a l ^ r i g i d . B o t h the m o n o X X I I a n d bis X X I I I

complexes

of p l a t i n u m ( I I )

show

1 9 5

Ρ ί - Ή c o u p l i n g s t h r o u g h three b o n d s to

the

acetate m e t h y l e n e protons a n d to the N - s u b s t i t u t e d groups. N o analogous c o u p l i n g s w e r e f o u n d w i t h the R h ( I I I ) chelates. C o m p l e x changes as the p H is r a i s e d w i t h the c o n c o m i t a n t f o r m a t i o n of h y d r o x o a n d p r o b a b l y p o l y n u c l e a r species.

occur

complexes

T h e s e changes c a n b e f o l l o w e d

con­

v e n i e n t l y w i t h the p r o t o n resonance spectra, a l t h o u g h a d e t a i l e d i n t e r ­ p r e t a t i o n of the effects is v e r y difficult.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

111

Compounds

E M

2XHI

T h e i n t e r a c t i o n of cations f o r m e d f r o m the p l a t i n u m g r o u p metals Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

w i t h solvents l i k e a c e t o n i t r i l e , d i m e t h y l s u l f o x i d e , a n d other c o n t a i n i n g m e t h y l protons is s t u d i e d easily w i t h Ή complexes

are r a t h e r inert. O ' B r i e n , G l a s s , a n d R e y n o l d s

m i n e d the s o l v a t i o n n u m b e r of ( H N ) P t 3

2

2 +

molecules

N M R , since these deter­

(42)

i n acetonitrile solution from

the p r o t o n resonance spectra of solutions of a n h y d r o u s ( H N ) P t ( C 1 0 ) . 3

2

4

2

B o t h b o u n d a n d b u l k a c e t o n i t r i l e resonances w e r e o b s e r v e d w i t h n o e v i ­ d e n c e for a n y exchange b r o a d e n i n g to 8 1 ° , the b o i l i n g p o i n t of aceto­ n i t r i l e . C o u p l i n g of the l i g a n d protons w i t h the p l a t i n u m n u c l e u s leads to the u s u a l 1:4:1 t r i p l e t , / ( 4

1 9 5

Ρί-Ή)

=

12.1 H z . I n t e g r a t i o n of

c o m p o n e n t of the t r i p l e t for the b o u n d solvent r e l a t i v e to the b a n d of the b u l k solvent gave a s o l v a t i o n n u m b e r of 2.0 ±

1 3

one

C side

0.1. It also

was possible to d e t e r m i n e a p p r o x i m a t e l y the r e l a t i v e integrals of

the

amine and

are

a c e t o n i t r i l e protons,

v e r y b r o a d because of the

1 4

a l t h o u g h the

a m i n e resonances

N quadrupole moment.

a s o l v a t i o n n u m b e r of 2.0 =b 0.1, too.

T h i s m e t h o d gives

T h e r e was no shift i n the b u l k

solvent resonance as the c o n c e n t r a t i o n of [ ( H N ) P t ( N C C H ) ] ( C 1 0 ) 3

2

3

2

4

2

was v a r i e d , suggesting that there are no significant solvent interactions i n the a x i a l positions of p l a t i n u m . Anhydrous ( H N ) P t ( C 1 0 ) 3

3

4

2

also has b e e n s t u d i e d i n d i m e t h y l s u l f ­

oxide s o l u t i o n ( 5 5 ) , since M e S O is a n a m b i d e n t a t e l i g a n d a n d p r o b a b l y 2

coordinates via s u l f u r r a t h e r t h a n o x y g e n as is k n o w n to b e the case w i t h p a l l a d i u m . T h e m e t h y l p r o t o n resonance for the b o u n d D M S O is s h i f t e d 2.54 p p m u p f i e l d f r o m the b u l k solvent, a n d the l i g a n d exchange rate is n e g l i g i b l e at 3 5 ° . the b o u n d D M S O n u m b e r s of 2.0 ±

Integrations of the b u l k a n d b o u n d D M S O signals or a n d a m i n e p r o t o n resonances 0.1. T h e c o u p l i n g constant / (

1 9 5

b o t h gave s o l v a t i o n Ρΐ-Ή)

=

23.2 H z ,

a n d this l a r g e a v a l u e suggests that D M S O is b o u n d via s u l f u r a n d n o t oxygen—i.e., t h a t the c o u p l i n g is t h r o u g h o n l y three a n d n o t f o u r b o n d s . U n d o u b t e d l y , i s o l a t i o n of the c r y s t a l l i n e a d d u c t s ( H N ) P t ( C 1 0 ) 3

2

4

2

· 2B

f r o m s o l u t i o n w o u l d c o n f i r m these s t o i c h i o m e t r i c s ; h o w e v e r , these c o m ­ p o u n d s are v e r y explosive.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

112

PLATINUM

M c F a r l a n e and W h i t e (37)

GROUP

METALS

2

COMPOUNDS

h a v e n o t e d that d i m e t h y l s u l f o x i d e w i l l

replace M e S and M e S e w h e n [ ( M e L ) P t C l ] ( L = 2

AND

2

2

S, S e )

2

complexes

are d i s s o l v e d i n D M S O a c c o r d i n g to R e a c t i o n s 4 a n d 5. (Me L) PtCl 2

2

+

2

D M S O <± M e L +

(DMSO)(Me L)PtCl 2

Well-resolved

1 9 5

(DMSO)(Me L)PtCl

2

+

2

2

D M S O <=> M e L + 2

(DMSO) PtCl 2

(4)

2

(5)

2

Ρ ί - Ή c o u p l i n g ( D M S O p r o t o n s ) of 21 to 24 H z is o b ­

s e r v e d , i n d i c a t i n g t h a t the D M S O exchanges s l o w l y w i t h the b u l k solvent. P r o t o n m a g n e t i c resonance s p e c t r a h a v e b e e n u s e d to assign struc­ tures to the g e o m e t r i c a l isomers of R h C l ( N C C H ) , since t h e cis c o m ­ 3

3

3

p l e x gives a single resonance w h i l e the trans i s o m e r gives t w o

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

s e p a r a t e d b y 0.05 p p m ( 5 ) . the c o m p l e x

resonances

T h e s t o i c h i o m e t r y i n a c e t o n i t r i l e s o l u t i o n of

[ ( C H ) N ] [ R h C l 4 ( N C C H ) ] w a s established b y i n t e ­ 2

5

4

3

2

g r a t i o n of the b o u n d a c e t o n i t r i l e resonances w i t h respect to the t e t r a e t h y l a m m o n i u m m e t h y l or m e t h y l e n e signals. Since most of the complexes of the p l a t i n u m g r o u p metals are stereoc h e m i c a l l y r i g i d a n d l i g a n d s exchange v e r y s l o w l y , studies of stereochem­ i s t r y w i t h solutions are s t r a i g h t f o r w a r d . C a r e m u s t b e u s e d , h o w e v e r , i n i n t e r p r e t i n g s p e c t r a of o r g a n i c d e r i v a t i v e s of these metals, since m a n y of t h e m are n o t r i g i d .

Dynamic Systems T h e N M R m e t h o d for s t u d y i n g the rates of m o d e r a t e l y fast r e a c ­ tions has f o u n d l i t t l e use w i t h the s t r i c t l y i n o r g a n i c complexes

of

the

p l a t i n u m g r o u p metals, since t h e y i n c l u d e m a n y of the most i n e r t c o m ­ plexes k n o w n .

T h e r e are, h o w e v e r , t w o types of c o m p o u n d s

of

these

metals w h i c h often are r a t h e r l a b i l e — i . e . , the organo a n d h y d r i d o d e r i v a ­ tives. F o r s u c h c o m p o u n d s , the N M R m e t h o d , a l t h o u g h less u s e f u l for s t e r e o c h e m i c a l studies, is p r o v i n g v e r y v a l u a b l e for s t u d y i n g r e a c t i o n rates. T h e t r i m e t h y l p l a t i n u m ( I V ) species p r o v i d e a p a r t i c u l a r l y clear ex­ a m p l e of the effects d e s c r i b e d above.

Octahedral inorganic

complexes

of p l a t i n u m ( I V ) are v e r y i n e r t to l i g a n d s u b s t i t u t i o n , a n d the fact that s u c h reactions o c c u r num (II)

at a l l is often a t t r i b u t a b l e to catalysis b y

impurities (3).

T h e o r g a n o m e t a l l i c complexes

plati­

[(CH ) PtL ] 3

3

3

u n d e r g o s u b s t i t u t i o n reactions of the L l i g a n d s v e r y r a p i d l y as a r e s u l t of the c o o r d i n a t i o n of the three p o l a r i z a b l e " m e t h i d e " l i g a n d s . G l a s s a n d Tobias

(20)

Pt(OH ) ] 2

3

+

s t u d i e d the rate of w a t e r exchange

between

[(CH ) 3

3

a n d the b u l k solvent u s i n g oxygen-17 N M R a n d f o u n d the

average l i f e t i m e of a w a t e r m o l e c u l e b o u n d to ( C H ) P t to b e o n l y ca. 3

9 Χ

10"

5

sec at 2 5 ° .

3

+

A p p r o x i m a t e expressions w e r e u s e d to relate the

l i n e shapes to the p s e u d o first o r d e r rate constant.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

113

Compounds

T h e first a p p l i c a t i o n s of N M R to the s t u d y of d y n a m i c systems of the p l a t i n u m g r o u p metals a p p e a r to h a v e b e e n studies o n the r o t a t i o n a b o u t the m e t a l - o l e f i n b o n d of c o o r d i n a t e d olefins, a n d this process has b e e n i n v e s t i g a t e d b y m a n y w o r k e r s . T h e r e are t w o r e a s o n a b l e o r i e n t a ­ tions of a n olefin w i t h respect to t h e rest of a s q u a r e p l a n a r c o m p l e x ,

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

X X I V and X X V .

M o s t of the g r o u n d states of complexes seem to h a v e s t r u c t u r e X X I V , b u t X X V r e a s o n a b l y c o u l d p r o v i d e a m e c h a n i s m for r o t a t i o n a b o u t t h e metal—olefin b o n d axis w i t h a l o w e n e r g y b a r r i e r .

C r a m e r (11)

found

that 7 T - c y c l o p e n t a d i e n y l b i s ( e t h y l e n e ) r h o d i u m ( I ) , X X V I , gave t w o b r o a d signals (τ =

7.23, 8.88 p p m ) for the e t h y l e n e protons at —25° a n d t h a t

3X2L u p o n h e a t i n g these coalesced to a single resonance (τ = 57°.

8.07 p p m )

at

T h e most l i k e l y process w h i c h w o u l d l e a d to e q u i v a l e n c e of a l l of

the e t h y l e n e protons is r o t a t i o n of the e t h y l e n e m o l e c u l e s

about

the

r h o d i u m - o l e f i n b o n d , since the c o m p l e x e x h i b i t s no m e a s u r a b l e exchange w i t h free e t h y l e n e after h e a t i n g for five h o u r s at 100°. I n contrast to the results w i t h the c y c l o p e n t a d i e n y l d e r i v a t i v e , a c e t y l a c e t o n a t o b i s ( e t h y l e n e ) r h o d i u m ( I ) , X X V I I shows a s i n g l e c o a l e s c e d s i g ­ n a l for the e t h y l e n e protons at 2 5 ° , a n d o n l y u p o n c o o l i n g to —58° are t w o signals o b s e r v e d at τ =

6.42 a n d 7.49 p p m (11).

I f e t h y l e n e is a d d e d

to the c o l d s o l u t i o n , o n l y a s i n g l e resonance for b o u n d a n d free e t h y l e n e is o b s e r v e d at τ =

ca. 6.95 p p m .

T h u s , the e t h y l e n e exchanges r a t h e r

r a p i d l y e v e n at — 5 8 ° , a n d a b i m o l e c u l a r process is i n d i c a t e d . T h e a n i o n of Z e i s e s salt, [ ( C H 4 ) P t C l ] - , a n d free e t h y l e n e i n m e t h a n o l i c HC1 also 2

3

e x h i b i t o n l y one p r o t o n resonance at t e m p e r a t u r e s as l o w as —75°

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

(10),

114

PLATINUM

GROUP

METALS

AND

COMPOUNDS

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

H

a n d the τ v a l u e is a f u n c t i o n of the [ ( C H 4 ) P t C l 3 ] " : C H 4 m o l e r a t i o . 2

2

C o n s e q u e n t l y , e x c h a n g e is v e r y r a p i d w i t h this c o m p l e x , too.

O n e pos­

s i b l e e x p l a n a t i o n of the fact that ( 7 r - C 5 H ) R h ( C H ) 2 does not exchange 5

2

4

ethylene at a m e a s u r a b l e rate is that t h e π-cyclopentadienyl g r o u p f u n c ­ tions as a six-electron donor, m a k i n g the c o m p l e x m u c h less susceptible to n u c l e o p h i l i c attack (11, Reaction (C H )S0 . 2

4

of

12).

(7r-C H )Rh(C H ) 5

5

2

4

2

w i t h S0

2

yields

(7r-C H )Rh5

resonance at — 2 ° , τ =

6.68 p p m , b u t u p o n c o o l i n g to — 5 0 ° , t w o reso­

nances t y p i c a l of a n A B 2

Recently, Cramer,

reinvestigated ( 7 r - C H 5 ) R h ( C H ) , X X V I , a n d 5

(7r-C H5)Rh(C H4)S0 5

s p e c t r u m are o b s e r v e d (12).

2

K l i n e , a n d R o b e r t s (13) 2

2

2

4

2

u s i n g m o r e p r e c i s e equations for the v a r i a t i o n

of l i n e shape w i t h l i f e t i m e a n d o b t a i n e d 15.0 ±

0.2 a n d 12.2 ±

m o l e , r e s p e c t i v e l y , for t h e a c t i v a t i o n energies

for r o t a t i o n .

C H )Rh(C F )(C H ),

±

5

5

5

A g a i n , this c o m p o u n d shows o n l y a single ethylene p r o t o n

2

2

4

2

the b a r r i e r w a s

4

13.6

0.8 k c a l / With

0.6 k c a l / m o l e .

(πThe

r e d u c t i o n of the b a r r i e r to r o t a t i o n u p o n s u b s t i t u t i o n of e l e c t r o n - w i t h ­ d r a w i n g groups, e.g., C F , is consistent w i t h a r e d u c t i o n i n b a c k b o n d i n g . 2

4

B r a u s e , K a p l a n , a n d O r c h i n (4) styrene a n d f e r f - b u t y l e t h y l e n e

e x a m i n e d the b a r r i e r to r o t a t i o n of

i n 2 , 4 , 6 - t r i m e t h y l p y r i d i n e complexes

platinum (II), X X V I I I .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

of

8.

TOBIAS

NMR

Spectra

of

115

Compounds

T h e p r o t o n resonance of the o - m e t h y l protons of the 2 , 4 , 6 - t r i m e t h y l p y r i d i n e l i g a n d b o u n d trans to styrene is a s i n g l e t r i p l e t [ / (

1 9 5

Pt-CH ) 3

=

13 H z ] at r o o m t e m p e r a t u r e , b u t i t splits into t w o o v e r l a p p i n g t r i p l e t s at —60°.

S i m i l a r b e h a v i o r is f o u n d w i t h i e r f - b u t y l e t h y l e n e . S i n c e the c o u ­

p l i n g b e t w e e n p l a t i n u m a n d the olefin protons ( /

1 9 5

Ρί-Ή =

ca. 10 H z )

is m a i n t a i n e d for the coalesced s i g n a l , the process was a s s u m e d to i n v o l v e i n t e r n a l r o t a t i o n a b o u t the e t h y l e n e - p l a t i n u m b o n d ; h o w e v e r , i t n o w is k n o w n that the p y r i d i n e l i g a n d s are b o u n d q u i t e w e a k l y because of the large trans influence of

ethylene.

Kaplin, Schmidt, and Orchin

s t u d i e d the exchange of s u b s t i t u t e d p y r i d i n e s a n d olefin i n

(31)

complexes

analogous to X X V I I I . A t r o o m t e m p e r a t u r e , the p y r i d i n e bases exchange r a p i d l y o n the P M R t i m e scale, p r o b a b l y b y b o t h dissociative a n d b i m o Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

lecular mechanisms.

T h e olefins are s t i l l sufficiently s t r o n g l y b o u n d

to

give s p i n - s p i n c o u p l i n g w i t h p l a t i n u m - 1 9 5 . H o l l o w a y , H u l l e y , J o h n s o n , a n d L e w i s (26) of several olefins i n the p l a t i n u m ( I I )

have observed rotation

complexes of t y p e X X I X .

ethylene protons, t w o o v e r l a p p i n g t r i p l e t resonances o b s e r v e d at l o w temperatures, τ = curs at — 2 8 ° C .

The

1 9 5

(

1 9 5

5.48 a n d 5.53 p p m .

F o r the

P t c o u p l i n g ) are Coalescence

P t c o u p l i n g persists after coalescence.

oc­

Free en­

ergies of a c t i v a t i o n for the r o t a t i o n a l process r a n g e f r o m 10.9 k c a l / m o l e w i t h t e t r a m e t h y l e t h y l e n e to 15.8 k c a l / m o l e w i t h trans but-2-ene. A n u m b e r of studies h a v e b e e n m a d e of the exchange of c o o r d i n a t e d a n d free l i g a n d s . E a t o n a n d Suart (16)

used

3 1

P N M R to e x a m i n e the

extent of d i s s o c i a t i o n of c h l o r o t r i s ( t r i p h e n y l p h o s p h i n e ) r h o d i u m ( I ) CH C1 2

2

solution. A t r o o m t e m p e r a t u r e , the c o m p l e x shows t w o

3 1

in

P reso­

nances for the trans a n d the t w o cis p h o s p h i n e s , a n d these are s p l i t b y i n t e r a c t i o n w i t h the

1 0 3

R h and

3 1

P n u c l e i . A d d i t i o n of excess t r i p h e n y l -

p h o s p h i n e has no effect o n the c o m p l e x s p e c t r u m , a n d exchange is s l o w o n the N M R t i m e scale.

D i s s o c i a t i o n , 6, w h i c h w a s suggested o n the basis

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

116

PLATINUM

Rh(PPh ) Cl + CH C1 3

3

2

2

10" M.

METALS

AND

COMPOUNDS

<± R h ( P P h ) C l ( C H C l ) + P P H 3

of m o l e c u l a r w e i g h t d a t a (43), at concentrations >

GROUP

2

2

2

(6)

3

occurs o n l y to the extent of less t h a n 5 %

M i x t u r e s of tris ( p - t o l y l ) p h o s p h i n e a n d tris-

2

( t r i p h e n y l p h o s p h i n e ) r h o d i u m c h l o r i d e g i v e p - t o l y l m e t h y l resonances o w i n g to tris ( p - t o l y l ) p h o s p h i n e s b o u n d b o t h cis a n d trans at

—35°.

T h e s e are c o l l a p s e d at 0 ° , a n d at 35° i n the presence of excess t r i s ( p t o l y l ) p h o s p h i n e , the l i g a n d resonance is a v e r a g e d o v e r b o t h b o u n d a n d free p h o s p h i n e . T h e a c t i v a t i o n energy for the i n t r a m o l e c u l a r exchange of t h e cis a n d trans p h o s p h i n e s is ca. 6 k c a l / m o l e , a n d this process is a p p r e c i a b l y faster t h a n the exchange b e t w e e n free a n d b o u n d p h o s p h i n e .

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

D e e m i n g a n d S h a w (43)

h a v e s t u d i e d the exchange of d i m e t h y l -

p h e n y l p h o s p h i n e w i t h complexes of the t y p e =

tons

RhX(CO) (PR ) , X 3

2

h a l i d e , X X X . T h e l i g a n d m e t h y l resonance gives a t r i p l e t because of

c o u p l i n g w i t h b o t h p h o s p h o r u s n u c l e i , w h i c h is s p l i t f u r t h e r b y c o u p l i n g

XXX

w i t h the r h o d i u m n u c l e u s / ( 3

1 0 3

Rh- H) =

c o u p l i n g i n trans bis ( p h o s p h i n e ) chemistry.

A d d i t i o n of

1 H z . See the d i s c u s s i o n of

1

complexes

i n the section o n

stereo­

sufficient d i m e t h y l p h e n y l p h o s p h i n e to

give

a

1:10 l i g a n d : c o m p l e x m o l e r a t i o causes the t r i p l e t to collapse because of exchange of b o u n d a n d free p h o s p h i n e . O n l y a b r o a d singlet is o b s e r v e d . T h e v a n i s h i n g of the c o u p l i n g w i t h Ή ) bound a n d / ( 2

3 1

Ρ-Ή)

Ϊ Γ Θ β

3 1

P, I =

1/2, i n d i c a t e s t h a t / ( 2

3 1

P-

are of o p p o s i t e s i g n a n d t h a t t h e y average

to zero. T h i s is s u p p o r t e d b y t h e o b s e r v a t i o n t h a t the a d d i t i o n of m o r e p h o s p h i n e leads to the e x p e c t e d d o u b l e t a r i s i n g f r o m c o u p l i n g w i t h F a c k l e r a n d c o w o r k e r s (18, 19)

3 1

P.

h a v e u s e d the m e t h y l p r o t o n reso­

nances to d e t e r m i n e a c t i v a t i o n energies for the exchange of m e t h y l d i p h e n y l p h o s p h i n e c o o r d i n a t e d to the bis-complexes of p l a t i n u m ( I I ) ligands (18),

such

as

p-dithiocumate

X X X I , a n d o-benzylxanthate

(18),

with

3,4,5-trimethoxydithiobenzoate

(19).

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

8.

TOBIAS

NMR

Spectra

of

117

Compounds

XXXI The / (

1 9 5

Ρ ί - Ή ) c o u p l i n g , 3 9 - 4 0 H z , shows t h a t the p h o s p h i n e is

c o o r d i n a t e d to p l a t i n u m .

S i n c e i t o c c u p i e s a n a x i a l p o s i t i o n of the b a s ­

i c a l l y square p l a n a r c o m p l e x , the p h o s p h i n e is r a t h e r l a b i l e . A c t i v a t i o n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

energies for exchange of 4.2 a n d 19.7 k c a l / m o l e w e r e f o u n d w h e r e the l i g a n d was p - d i t h i o c u m a t e a n d 3,4,5-trimethoxydithiobenzoate,

respec­

tively. Y a g u p s k y a n d W i l k i n s o n ( 5 9 ) h a v e e x a m i n e d the h y d r i d e resonance of the 5-coordinate h y d r i d o d i c a r b o n y l b i s ( t r i p h e n y l p h o s p h i n e ) i r i d i u m ( I ) as a f u n c t i o n of t e m p e r a t u r e . T w o isomers a p p e a r to exist i n e q u i l i b r i u m , since the c o u p l i n g constant / ( P — Ή ) is c o n s i d e r a b l y s m a l l e r t h a n ex­ 2

3 1

p e c t e d for c o u p l i n g to a cis p h o s p h i n e

(1.5-8.5 H z , depending

solvent at 3 5 ° ) , a n d it is t e m p e r a t u r e - d e p e n d e n t .

upon

See the d i s c u s s i o n of

h y d r i d e - p h o s p h i n e c o u p l i n g i n cis a n d trans complexes

i n the section

o n stereochemistry. S i n c e the c o u p l i n g decreases to zero as the t e m p e r a ­ ture is l o w e r e d a n d t h e n increases a g a i n as the t e m p e r a t u r e d r o p s s t i l l further, i t appears t h a t the t w o isomers h a v e

3 1

Ρ - Ή c o u p l i n g constants of

opposite sign. A s the e q u i l i b r i u m b e t w e e n the isomers is shifted b y v a r y ­ i n g the t e m p e r a t u r e , there exists a t e m p e r a t u r e at w h i c h / averages to 0; i-e>,

XAJA

+

XBJB

=

0 where χ

Α

isomers a n d J a n d J are t h e i r A

B

and 3 1

X B

are the m o l e fractions of the t w o

Ρ - Ή c o u p l i n g constants.

S o m e c a u t i o n s h o u l d b e u s e d i n the i n t e r p r e t a t i o n of the a c t i v a t i o n parameters o b t a i n e d i n m a n y of these studies. P a r t i c u l a r l y i n the e a r l i e r w o r k , a p p r o x i m a t e equations r e l a t i n g l i n e shape to rate parameters often h a v e b e e n u s e d , so m a n y of the rates are b a s i c a l l y o r d e r of m a g n i t u d e values. T h e c u r r e n t use of c o m p u t e r s to d e t e r m i n e the best agreement b e t w e e n c a l c u l a t e d a n d o b s e r v e d spectra s h o u l d i m p r o v e the a c c u r a c y of these calculations. O t h e r factors s u c h as changes i n the c h e m i c a l shifts b e t w e e n t w o resonances w i t h t e m p e r a t u r e c a n cause l a r g e errors i n the a c t i v a t i o n energy.

Summary T h e p r i n c i p a l a p p l i c a t i o n of N M R i n the s t u d y of the

compounds

of the p l a t i n u m g r o u p metals is l i k e l y to c o n t i n u e to b e i n s t r u c t u r e d e -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

118

PLATINUM GROUP METALS AND COMPOUNDS

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

termination. As spectrometers suitable for heteronuclear double reso­ nance measurements become increasingly available, more information on the chemical shifts of the metal nuclei will be produced. NMR should prove extremely useful for the study of labile complexes of these elements, and it is precisely these systems which are of interest as catalytic inter­ mediates. This technique affords a convenient method for the study of intra- and intermolecular exchange processes. Literature Cited (1) Allen, F. H., Pidcock, Α., J. Chem. Soc. 1968, A, 2700. (2) Baird, M.C.,Mague, J. T., Osborn, T. Α., Wilkinson, G.,J.Chem. Soc. 1967, A, 1347. (3) Basolo, F., Pearson, R. G., "Mechanisms of Inorganic Reactions," 2nd ed., p. 238, Wiley, New York, 1966. (4) Brause, A. R., Kaplan, F., Orchin, M.,J.Am. Chem. Soc. 1967, 89, 2661. (5) Catsikis, B. D., Good, M. L., Inorg. Chem. 1969, 8, 1095. (6) Chatt, J., Coffey, R. S., Shaw, B. L.,J.Chem. Soc. 1965, 7391. (7) Clegg, D. E., Hall, J. R., Australian J. Chem. 1967, 20, 2025. (8) Clegg, D. E., Hall, J. R., Spectrochim. Acta 1967, 23A, 263. (9) Connick, R. E., Fiat, D. N.,J.Chem. Phys. 1963, 39, 1349. (10) Cramer, R., Inorg. Chem. 1965, 4, 445. (11) Cramer, R.,J.Am. Chem. Soc. 1964, 86, 217. (12) Ibid., 1967, 89, 5377. (13) Cramer, R., Kline, J. B., Roberts, J. D., J. Am. Chem. Soc. 1969, 91, 2519. (14) Dean, R. R., Green, J. C.,J.Chem. Soc. 1968, A, 3047. (15) Deeming, A. J., Shaw, B. L., J. Chem. Soc. 1969, A, 597. (16) Eaton, D. R., Suart, S. R.,J.Am. Chem. Soc. 1968, 90, 4170. (17) Emsley, J. W., Feeny, J., Sutcliffe, L. H., "High Resolution Nuclear Mag­ netic Resonance Spectroscopy," Vol. 2, p. 989, Pergamon, Oxford, 1966. (18) Fackler, J. P., Jr., Fetchin, J. Α., Seidel, W.C.,J.Am. Chem. Soc. 1969, 91, 1217. (19) Fackler, J. P., Jr., Seidel, W.C.,Fetchin, J. Α.,J.Am. Chem. Soc. 1968, 90, 2707. (20) Glass, G. E., Schwabacher, W. B., Tobias, R. S., Inorg. Chem. 1968, 7, 2471. (21) Glass, G. E., Tobias, R. S.,J.Am. Chem. Soc. 1967, 89, 6371. (22) Griffith, J. S., Orgel, L. E., Trans. Faraday Soc. 1957, 53, 601. (23) Grim, S. O., Ference, R. Α., Inorg. Nucl. Chem. Letters 1966, 2, 205. (24) Grim, S. O., Keiter, R. L., McFarlane, W., Inorg. Chem. 1967, 6, 1133. (25) Heaton, B. T., Pidcock, Α.,J.Organometal. Chem. 1968, 14, 235. (26) Holloway, C. E., Hulley, G., Johnson, B. F. G., Lewis, J.,J.Chem. Soc. 1969, A, 53. (27) Jenkins, J. M., Shaw, B. L.,J.Chem. Soc. 1966, A, 770. (28) Ibid., 1966, 1407. (29) Jenkins, J. M., Shaw, B. L., Proc. Chem. Soc. 1963, 279. (30) Jensen, Κ. Α., Ζ. Anorg. Allgem. Chem. 1936, 229, 252. (31) Kaplan, P. D., Schmidt, P., Orchin, M., J. Am. Chem. Soc. 1967, 89, 4537. (32) Kettle, S. F. Α.,J.Chem. Soc. 1965, 6664. (33) Kite, K., Smith, J. A. S., Wilkins, E. J., J. Chem. Soc. 1966, A, 1744. (34) Lydon, J. E., Truter, M. R.,J.Chem. Soc. 1965, 6899. (35) McFarlane, W., Chem. Commun. 1967, 772.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch008

8. TOBIAS

NMR Spectra of Compounds

119

(36) Ibid., 1968, 393. (37) Ibid., 1969, 439. (38) Ibid., 1969, 700. (39) McFarlane, W.,J.Chem. Soc. 1967, A, 1922. (40) McFarlane, W., Quart. Rev. 1969, 23, 187. (41) Morgan, G. L., Rennick, R. D., Soong, C. C., Inorg. Chem. 1966, 5, 372. (42) O'Brien, J. F., Glass, G. E., Reynolds, W. L., Inorg. Chem. 1968, 7, 1664. (43) Osborn, J. Α., Jardine, F. H., Young, J. F., Wilkinson, G., J. Chem. Soc. 1966, A, 1711. (44) Parshall, G. W.,J.Am. Chem. Soc. 1964, 86, 5367. (45) Ibid., 1966, 88, 704. (46) Pidcock, Α., Richards, R. E., Venanzi, L. M.,J.Chem. Soc. 1966, A, 1707. (47) Ibid., 1968, 1970. (48) Pidcock, Α., Richards, R. E., Venanzi, L. M., Proc. Chem. Soc. 1962, 184. (49) Pople, J. Α., Santry, D. P., Mol. Phys. 1964, 8, 1. (50) Ramsey, N. F., Phys. Rev. 1950, 78, 699. (51) Smith, Β. B., Sawyer, D. T., Inorg. Chem. 1969, 8, 379. (52) Ibid., 1968, 7, 922. (53) Ibid., 1968, 7, 1526. (54) Smith, J. A. S.,J.Chem. Soc. 1962, 4736. (55) Thomas, S., Reynolds, W. L., Inorg. Chem. 1969, 8, 1531. (56) Tobias, R. S., Inorg. Chem. 1970, 9, 1296. (57) Varian Associates, "NMR Table," 5thed.,1965. (58) Walton, R. Α.,J.Chem. Soc. 1967, A, 1852. (59) Yagupsky, G., Wilkinson, G.,J.Chem. Soc. 1969, A, 725. RECEIVED December 16, 1969.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

9

Crystal Structures of Complexes of the Platinum G r o u p Metals

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

E. L. AMMA University of South Carolina, Columbia, S. C. 29208

The crystal and molecular structure of selected groups of P metal complexes are reviewed and discussed. These stru tures are divided into three groups: molecular adducts, "squareplanar"Pt(II) complexes, and structures involving delocalizedπsystems. The molecular adducts of N , O , CO, and NO are classified (in general) into two types, either trigonal bipyramids or distorted tetragonal pyramids The geometry and bond lengths of thePt(II)complexes are discussed in terms of limitations imposed on discussions o bond lengths. The effect ofπelectrons on complex stereo chemistry is discussed in the remaining section. 2

+

'T^his summary of the x-ray structure determinations of Pt group metals is not to be construed as comprehensive. Rather, it should be viewed as recent structure determinations of Pt group metals of interest to the author; any omissions should be considered as limitations in the scope of interest of the author and not in the importance of the research omitted. The crystal structures of the Pt group metals to be examined fall readily into three categories : (1) New complexes where the stereochem­ istry about the metal atom is of interest, e.g., molecular adducts. These results are intrinsically of interest and importance to the nature of the chemical bonding in these molecules or ions. The inclusion of the struc­ tures of this class of compounds is particularly appropriate since their chemistry and kinetic properties are discussed elsewhere in this sym­ posium. (2) The "accurate" determination of bond lengths in order to investigate π bonding or the nature of metal-ligand bonds in general. (3) Pt metal structures containing, or potentially containing, delocalized 7Γ systems. A recent review containing a number of Pt structures is: Churchill, M. R., "Structural Studies on Transition Metal Complexes ConA

120 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

2

9.

AMMA

Crystal

Structure

of

121

Complexes

t a i n i n g σ-Bonded C a r b o n A t o m s " in "Perspectives i n S t r u c t u r a l C h e m ­ istry " J . D . D u n i t z a n d J . A . Ibers, E d s . , W i l e y , N e w Y o r k , 1970. It seems a p p r o p r i a t e at this t i m e to p u t f o r t h some c a u t i o n a r y state­ ments for the g e n e r a l reader c o n c e r n i n g these h e a v y m e t a l a t o m s t r u c ­ tures a n d t h e i r q u o t e d a c c u r a c y i n b o n d lengths. I n g e n e r a l , c r y s t a l l o g r a phers are w e l l a w a r e of the shortcomings of t h e i r d a t a . T h e q u o t e d errors i n b o n d lengths are the results of m a t h e m a t i c a l treatment of the d a t a a s s u m i n g n o u n c o r r e c t e d systematic errors.

A l l crystallographic data,

i n c l u d i n g m o d e r n counter d a t a c o l l e c t e d b y a u t o m a t e d diffractometers, c o n t a i n u n c o r r e c t e d systematic errors even after corrections for a b s o r p ­ t i o n , a n o m a l o u s d i s p e r s i o n , etc., h a v e b e e n m a d e . Some of the i n h e r e n t l y r e m a i n i n g errors are i n s t r u m e n t a l , i n v o l v i n g the m o n o c h r o m a t i c i t y of the Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

r a d i a t i o n , s t a b i l i t y a n d h o m o g e n e i t y of the source, as w e l l as the s t a b i l i t y of the detector a n d associated e l e c t r o n i c systems. ments are not to b e o v e r l o o k e d .

Mechanical misalign­

C r y s t a l s themselves m a y u n d e r g o r a d i a ­

t i o n d a m a g e d u r i n g the d a t a c o l l e c t i o n p e r i o d , a n d e v e n m o r e m u n d a n e occurrences s u c h as c r y s t a l m o v e m e n t c a n create serious difficulties for the u n w a r y . T h e t h e o r e t i c a l m o d e l s u s e d for the c a l c u l a t i o n of the x - r a y scattering b y electrons i n m o l e c u l e s h a v e t h e i r shortcomings

as w e l l .

T h e r m a l motions of atoms f r o m x-ray i n t e n s i t y d a t a of crystals are not w e l l understood.

( T h e r m a l e l l i p s o i d s of atoms are n o w c o m m o n i n m a n y

x-ray structure p u b l i c a t i o n s ; t h e y s h o u l d be i n t e r p r e t e d a n d , for that m a t ­ ter, a c c e p t e d

w i t h caution.)

We

suggest t h a t the p r a c t i c i n g c h e m i s t

m u l t i p l y the q u o t e d error b y t w o unless some q u a l i f y i n g statements h a v e b e e n m a d e , a n d w h e n m a k i n g comparisons b e t w e e n

bond

lengths i n

different structures, not consider differences significant unless t h e y are at least t w i c e this i n f l a t e d error. I n cases w h e r e d i s o r d e r or u n u s u a l l y l a r g e t h e r m a l m o t i o n is r e p o r t e d , one is w e l l a d v i s e d to be e v e n m o r e servative.

con­

P r i o r to a p p r o x i m a t e l y five to six years ago, almost a l l d a t a

were collected by photographic techniques, a n d photographic data have e v e n m o r e i n n a t e systematic errors. H e n c e , a n y d e t a i l e d d i s c u s s i o n a b o u t s m a l l differences i n b o n d lengths f r o m d a t a before a n d p h o t o g r a p h i c d a t a after that date s h o u l d be m a d e w i t h c a u t i o n . N e v e r t h e l e s s , there is n o other m e t h o d of structure d e t e r m i n a t i o n w i t h a c o m p a r a b l e m a g n i t u d e of r e l i a b i l i t y for the d e t e r m i n a t i o n of structures of m o d e r a t e to c o m p l i ­ c a t e d molecules.

Molecular 0 of 0 (37)

2

2

Adducts Adducts.

Ibers continues his excellent s t r u c t u r a l investigations

a d d u c t s w h i c h started w i t h [ ( C H ) P ] 2 l r C O Z i n w h i c h Ζ = 6

a n d I (44).

s o l v e d (71).

5

3

Cl

T h e s t r u c t u r e of the B r isomer has also b e e n r e c e n t l y

T h e s e studies b y Ibers et al. h a v e b e e n e x t e n d e d to i n c l u d e

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

122

PLATINUM

GROUP

METALS

AND

COMPOUNDS

Inorganic Chemistry

Figure 1. The local environment about the Ir atom in [(C H ) ?'\ Ir COCl · 0 6

5 3

B

2

Bond length errors: Ir-P ± 0.008A, Ir-I ± 0.005A, Ir-O ± 0.02A, O-O ± 0.026A. Angle errors are 0.7° or less. (Ref. 44)

the o x y g e n a d d u c t s of [ ( C H ) P ( C H 2 ) ] 2 l r ( P F - ) 6

P(CH )] Rh (PF -) 2

the 0

2

2

+

6

5

+

2

a d d u c t of [ ( C H 5 ) ( C 2 H ) P ] I r C O C l ( 7 7 ) . 6

pictorial purposes) 0

2

[(C H ) -

{45,46),

6

6

5

2

O t h e r w o r k e r s h a v e s o l v e d t h e structure of

(46). 2

5

Considering (for

2

as a u n i d e n t a t e l i g a n d , t h e structures of t h e first

three a n d t h e v e r y last c o m p l e x c a n b e d e s c r i b e d as t r i g o n a l b i p y r a m i d a l w i t h trans a p i c a l phosphines w h i l e C O a n d Ζ a c c o m p a n y the 0

molecule

2

i n the t r i g o n a l p l a n e ( F i g u r e 1 ) . T h e geometry of t h e c h e l a t e d d i p h o s , [ b i s ( l , 2 - d i p h e n y l p h o s p h i n o ) e t h a n e ] R h a n d I r complexes m a y b e d e ­ s c r i b e d i n a n analogous O f considerable

manner.

c h e m i c a l a n d p o t e n t i a l l y of b i o l o g i c a l

is t h e c h a n g e i n ease w i t h w h i c h t h e 0 parent complex

2

importance

m o l e c u l e c a n b e a d d e d to t h e

as a f u n c t i o n of l i g a n d s a n d c e n t r a l m e t a l i o n . T h e

changes i n b o n d lengths ( O - O a n d M - O ) have b e e n c o r r e l a t e d w i t h t h e r e v e r s i b i l i t y o f o x y g e n u p t a k e (46).

T h e m o r e electronegative t h e l i g a n d

Ρ < I < B r < C I , t h e less is t h e b a c k d o n a t i o n of electrons i n t o t h e 0 l i g a n d f r o m t h e m e t a l , a n d t h e O - O distance is m o r e l i k e free 0 .

2

Like­

2

w i s e , t h e p o o r e r t h e energy m a t c h b e t w e e n m e t a l a n d o x y g e n o r b i t a l s , the m o r e l i k e free 0 Rh0

2

+

2

is the c o o r d i n a t e d oxygen—i.e., i n [ ( C H ) P ( C H ) ] 6

5

2

2

, the O - O b o n d l e n g t h is shorter t h a n i n [ ( C H ) P ( C H ) ] I r 0 6

5

2

2

2

2

2

+

.

T h i s e x p l a n a t i o n is i n agreement w i t h t h e facts, b u t t h e n a t u r e o f t h e metal-oxygen

bond

is p r o b a b l y

more complex

a n d m o r e sensitive to

subtle changes at t h e m e t a l t h a n this s i m p l e p i c t u r e indicates.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

F o r ex-

9.

Crystal

A M M A

Structure

of

123

Complexes

a m p l e , there is the v a r i a t i o n i n I r - P d i s t a n c e of 0.17A i n the P(CH )] M) 2

2

2

(45,

+

[(C H ) 6

5

2

c o m p l e x , b u t n o significant difference i n R h - P

46)

b o n d lengths i n the analogous R h a d d u c t . F u r t h e r m o r e , the O - O d i s t a n c e of 1 . 6 3 ( 2 ) A i n this I r - 0 1.48(2)A i n H 0 2

2

a d d u c t is longer t h a n the 0

o n e considers m i x i n g of e x c i t e d states of 0 lation 0 " . 2

distance

2

of

H o w e v e r , this distance m a y b e u n d e r s t o o d i f

(76).

2

r a t h e r t h a n the i o n i c f o r m u ­

2

I n a d d i t i o n , the O - O distance is s u r p r i s i n g l y sensitive to

2

changes i n the p h o s p h i n e g o i n g f r o m 1 . 3 0 ( 3 ) A i n [ ( C H ) P ] I r C O C l · 6

0

to 1 . 5 4 ( 4 ) A i n [ ( C H ) ( C H ) P ] I r C O C l · 0

(37)

2

6

5

2

2

5

2

5

t i o n to these structures, the s t r u c t u r e of [ ( C H ) P ] P t 0 6

5

3

3

2

2

2

2

(77).

I n rela­

(34)

is i n t e r ­

esting. I n this case the m e t a l , t w o p h o s p h o r u s , a n d t w o o x y g e n atoms l i e i n t h e same p l a n e a c c o m p a n i e d b y P t - O distances of 2 . 0 1 ( 3 ) A a n d a n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

O - O distance of 1 . 4 5 ( 4 ) A .

T h i s P t - O distance is w i t h i n the r a n g e of

I r - O distances f o u n d b y Ibers, b u t the O - O d i s t a n c e is essentially that e x p e c t e d for 0 ~ . 2

S i n c e this c o m p l e x does not i n a n y sense of t h e t e r m

2

reversibly a d d 0

2

d e s c r i b e d as P t

with 0 ~.

2 +

a n d the g e o m e t r y 2

2

is " s q u a r e p l a n a r , " i t s h o u l d

be

S u p p o r t for this f o r m u l a t i o n is f o u n d i n the

structure of tris ( t r i p h e n y l p h o s p h i n e ) c a r b o n y l p l a t i n u m w h i c h m a y

be

d e s c r i b e d as t e t r a h e d r a l ( i ) — i . e . , P t ( O ) . N

T h e c r y s t a l structures of three n i t r o g e n adducts h a v e

Adducts.

2

b e e n s o l v e d a n d r e p o r t e d at this t i m e . Ibers a n d c o w o r k e r s h a v e d e t e r ­ m i n e d the structures of C o H ( N ) [ P ( C H ) ] 2

[ N H ( C H ) N H ] } P F " (15). 2

2

2

2

2

+

6

5

3

3

(16)

and

{Ru(N )(N )3

2

T h e e n v i r o n m e n t a b o u t the c o b a l t a t o m

6

is t r i g o n a l b i p y r a m i d a l w i t h the three p h o s p h o r u s atoms i n the t r i g o n a l p l a n e , whereas the N

2

m o l e c u l e a n d the h y d r i d e are i n the a p i c a l p o s i ­

tions. I n contrast, the R u is six-coordinate. T h e M - N - N angle i n b o t h cases is 180°, a n d the N

2

m o l e c u l e is b o u n d e n d - o n to the m e t a l , as is the

C O m o i e t y i n c a r b o n y l complexes.

T h e C o - N b o n d l e n g t h of 1 . 8 0 ( 1 ) A

av. also denotes some metal—nitrogen m u l t i p l e b o n d i n g . T h e structure of Ru(NH ) N Cl 3

5

2

was s o l v e d b y N y b u r g a n d B o t t o m l y (13),

2

a n d t h e y also

r e p o r t a six-coordinate R u w i t h a l i n e a r R u - N - N arrangement.

However,

this structure is c o m p l i c a t e d b y d i s o r d e r . S0 the S 0 (53).

2

2

and C S Adducts. Ibers et al. h a v e p u b l i s h e d the structures of 2

a d d u c t s of [ ( C H ) P ] M - C O C l i n w h i c h M = 6

5

3

2

I r (36)

or R h

T h e stereochemistry of the m e t a l atoms is that of a t e t r a g o n a l

p y r a m i d w i t h C O , C I , a n d trans Ρ atoms i n the b a s a l p l a n e a n d S of the S0

2

g r o u p at the apex.

T h e M—S vector i n these c o m p o u n d s makes a n

angle of — 3 0 ° w i t h the n o r m a l to the S 0

2

p l a n e . N o t e t h e difference

b e t w e e n this geometry a n d that of the analogous 0 a n d W i b e r l y (80)

2

adducts. Vogt, K a t z ,

r e p o r t e d the c r y s t a l structure of [ R u C l ( N H ) S 0 ] C l 3

4

2

w h e r e i n the R u is " o c t a h e d r a l l y " c o o r d i n a t e d w i t h C I trans to S. T h e S of the S 0

2

g r o u p is t i l t e d s i m i l a r l y to that f o u n d i n the a b o v e - m e n t i o n e d

I r a n d R h complexes.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

124

PLATINUM

GROUP

METALS

AND

COMPOUNDS

T h e c r y s t a l s t r u c t u r e o f the c a r b o n d i s u l f i d e a d d u c t of [ ( C H ) P ] P t 6

has b e e n s o l v e d (42). s u l f u r of the C S

group.

2

5

3

3

I n this case, the P t is b o u n d to a c a r b o n a n d o n e T h e P t a t o m a n d its f o u r d i r e c t l y - b o u n d n e i g h ­

bors are c o p l a n a r , b u t the u n b o u n d s u l f u r is t i p p e d out of t h i s p l a n e . F u r t h e r m o r e , the C S

m o l e c u l e is b e n t w i t h a S - C - S a n g l e of

2

136(4)°.

It is a n i n t e r e s t i n g q u e s t i o n i n this case as to the o x i d a t i o n state of the m e t a l r e l a t i v e to t h e g e o m e t r y of the c o m p l e x . Tetracyanoethylene Adducts ( T C N E ) . T h e structure of the t e t r a c y a n o e t h y l e n e a d d u c t ( 4 5 ) of [ ( C H ) P ] I r C O B r has b e e n d e t e r m i n e d , 6

a n d i n contrast to the 0

5

3

2

a d d u c t , a l t h o u g h the stereochemistry a b o u t I r

2

is also t r i g o n a l b i p y r a m i d a l w i t h the C = C

i n the e q u a t o r i a l p l a n e , the

p h o s p h i n e s are cis a n d i n t h e e q u a t o r i a l p l a n e .

The C = C

distance i n

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

t h e a d d u c t is 0.18A longer t h a n i n free t e t r a c y a n o e t h y l e n e a n d the T C N E e n t i t y is n o n p l a n a r .

T h e s e facts c a n b e r e a d i l y i n t e r p r e t e d as t h e I r

d o n a t i n g c h a r g e i n t o the π* o r b i t a l of T C N E . T h e s t r u c t u r e of I r ( C N H ) 6

CO(TCNE)[P(C H ) ]2 6

5

4

is v e r y s i m i l a r to t h e a b o v e except t h a t

(60)

3

t h e a x i a l I r - B r i n t e r a c t i o n is r e p l a c e d b y a n I r — N s i g m a b o n d f r o m a m o d i f i e d T C N E l i g a n d . I n contrast, the structure of the P t [ P ( C H ) ] 2 6

TCNE

complex yields an approximately planar P t P C

(12)

2

a g a i n , as i n the C S

2

2

5

3

unit and

a d d u c t of P t ( O ) , a n u n u s u a l stereochemistry.

Nitrosyl Adducts. T h r e e structures c a n be r e l a t e d to the I r C O C l [ P (C H ) ] 6

5

3

· S0

2

structure directly—i.e., they have a tetragonal p y r a m i d

2

structure w i t h a bent axial M - N - O grouping. These are: { I r l ( C O ) ( N O ) [P(C H ) ] }BF -C H 6

32),

5

3

2

4

6

{IrCl(CO) (NO) [ P ( C H ) ] } B F

(31),

6

6

and R u C l ( N O ) [ P ( C H ) ] P F (59). 2

6

5

3

2

6

5

3

2

4

(30,

I n the latter s t r u c t u r e , the

o n l y significant difference is that one of t h e N O groups is i n the b a s a l plane w i t h a linear R u - N - O complex.

g r o u p i n g s i m i l a r to t h e C O of t h e

S0

2

A l i n e a r M - N - O a r r a n g e m e n t w a s also f o u n d i n " o c t a h e d r a l "

OsCl (HgCl)NO[P(C H ) ]2 2

6

5

Ir(NO)2[P(C H ) ] C10 6

5

3

2

(7).

2

4

O n the other h a n d , the s t r u c t u r e of

consists of a d i s t o r t e d t e t r a h e d r o n of the

(52)

nearest n e i g h b o r atoms a b o u t I r w i t h almost l i n e a r I r - N - O g r o u p i n g s . C O Adducts. T h i s is s o m e w h a t u n u s u a l t e r m i n o l o g y , b u t w e restrict this b r i e f d i s c u s s i o n to m o l e c u l e s r e l a t e d to the a b o v e . T h e structures of IrCl(CO)2[P(C H5) ] 6

3

2

· C H 6

6

(58)

and O s ( C O ) [ P ( C H ) ] 3

6

5

3

2

have been

d e t e r m i n e d , a n d t h e y are t r i g o n a l b i p y r a m i d a l , as is

analogous 0

2

(73) the

a n a l o g of the f o r m e r of t h e t w o m e n t i o n e d h e r e i n e x c e p t

that C O is b o u n d e n d - o n i n b o t h cases.

Stereochemistry and Bond Lengths in Pt(II) Complexes B a s o l o a n d P e a r s o n (5b)

as p a r t of a d i s c u s s i o n of the k i n e t i c trans

effect ( f o r d e f i n i t i o n see R e f . 5a)

e s t a b l i s h e d a q u a l i t a t i v e trans i n f l u e n c e

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

9.

Crystal

A M M A

Structure

of

125

Complexes

series b y n o t i n g the P t - X b o n d l e n g t h as a f u n c t i o n of the trans p a r t n e r L in L - P t - X .

T h e r e s u l t i n g series is q u i t e s i m i l a r to the k i n e t i c trans

effect series. H o w e v e r , i t is n o w g e n e r a l l y a c c e p t e d t h a t the trans effect is a n o u t d a t e d c o n c e p t w h e n v i e w e d i n terms of the details of t h e elec­ t r o n i c structure of the c o m p l e x a n d a c t i v a t e d i n t e r m e d i a t e s (35,

85).

T h e d a t a o n b o n d lengths u s e d i n the series b y B a s o l o a n d P e a r s o n are i n t e r e s t i n g examples of o l d e r d a t a t h a t h a v e b e e n u s e d to d r a w c o n ­ clusions.

( T h i s is not to find f a u l t w i t h B a s o l o a n d P e a r s o n ; that's a l l

they h a d ! ) modern

A n u m b e r of these structures h a v e b e e n r e d e t e r m i n e d

methods

a n d the earlier w o r k w a s

found

to

be

by

unreliable.

F u r t h e r m o r e , the use of the t e r m trans-influence is s t i l l to b e f o u n d i n the l i t e r a t u r e as a b o n d l e n g t h feature. Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

T h e most s t r i k i n g e x a m p l e of the difference b e t w e e n earlier w o r k a n d the m o r e recent structure (9, 33)

(11, 47, 48)

Zeise's salt ( K P t C l

3

•C H 2

4

· H 0) 2

refinement is that of

( F i g u r e 2 ) . T h e o l d e r results s h o w e d

a P t - C l b o n d l e n g t h of 2.42A for C I trans to C H 2

4

a n d a 2.32A P t - C l b o n d

l e n g t h for C I trans to C I . A s c a n b e seen i n F i g u r e 2, t h e r e are n o s i g ­ nificant differences b e t w e e n the three P t - C l distances. A " n o r m a l " P t - C l single b o n d l e n g t h m a y be t a k e n as 2.30A (41,

This particular

49, 57).

c o m p o u n d w a s u s e d for some t i m e as the e x a m p l e for ττ-bonding a n d trans influence!

T h e P t - C l b o n d l e n g t h trans to ethylene i n d i p e n t e n e P t ( I I )

c h l o r i d e (4)

is 2 . 3 3 ( 1 ) A , b u t is r a r e l y referenced.

T h e t e r m trans i n f l u -

Cl(3)

Acta Crystallographica

Figure 2. The local environment Pt atom in Zieses salt [KPtCl C H 3

2

i

about the · H 0] 2

Bond length errors: Pt-Cl(l) ± 0.004A, Pt-Cl(2), Cl(3) ± 0.020A, Pt-C ± 0.020A. Angle errors are 0.6° or less. (Ref. 9) A more recent refinement (private communication from P. G. Owston) makes the distances as follows: Pt-CUl) 2,327(5) A Ptr-Cl(2) 2.314(7) A Pt-Cl(3) 2.296(7) A

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

126

PLATINUM

GROUP

METALS

AND

COMPOUNDS

ence r e l a t i v e to b o n d lengths continues i n use b u t one m u s t b e a r i n m i n d that for s m a l l changes i n b o n d lengths a m u l t i t u d e of factors c a n r e s p o n s i b l e , s u c h as i o n i c forces i f t h e c o m p l e x is i o n i c , h y d r o g e n i n g , a n d m o l e c u l a r p a c k i n g , to n a m e a f e w .

I n t e r m o l e c u l a r forces a n d

t h e i r effect o n b o n d lengths a n d angles are m i n i m i z e d f o r

uncharged

complexes, a n d t h e most r e l i a b l e distances for c o m p a r i s o n purposes be o b t a i n e d f r o m these systems.

be

bond­

can

H o w e v e r , e v e n i n these cases, c a u t i o n

m u s t b e exercised; for e x a m p l e , the structure of t r a n s - d i c h l o r o b i s t r i p r o pylphosphine-WjW'-dichloroplatinum

(JO)

i n w h i c h the

center

of

the

c h l o r i n e - b r i d g e d d i m e r lies o n a center of s y m m e t r y . T h e P t - C l distance of t h e b r i d g i n g c h l o r i n e trans to the p h o s p h i n e g r o u p is l o n g at 2 . 4 2 5 ( 8 ) A and

the P t - P d i s t a n c e is " s h o r t " at 2 . 2 3 9 ( 9 ) A .

2 . 2 4 7 ( 7 ) A is o b s e r v e d i n c i s - P t [ P ( C H ) ] C l

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

3

3

2

2

A

P t - P distance

of

T h e e l o n g a t i o n of

(50).

t h e P t - C l distance f r o m the n o r m a l 2.30A is a t t r i b u t a b l e to t w o factors: ( a ) I n e v i t a b l y , the P t - C l distance w i t h the b r i d g i n g c h l o r i n e w i l l b e l o n g because of the h a l o g e n f o r m i n g t w o b o n d s a n d c o n s e q u e n t l y , b e a r i n g a n effective f o r m a l p o s i t i v e c h a r g e a n d ( b ) phosphine ( P t - C l i n c « - P t [ P ( C H ) ] C l 3

2

2

the fact that i t is trans to t h e 2

is 2 . 3 8 A ) .

The terminal P t - C l

distance is n o r m a l at 2 . 2 7 9 ( 9 ) A w i t h i n t w o s t a n d a r d d e v i a t i o n s .

There­

fore, care m u s t b e exercised i n terms of h o w m u c h b o n d l e n g t h e n i n g of the P t - C l b o n d is a t t r i b u t a b l e to the p h o s p h i n e alone. T h e structures of cis- a n d i m n 5 - d i c h l o r o d i a m m i n o p l a t i n u m ( I I ) d e t e r m i n e d b y M i l b u r n a n d Truter (51) simple

are the most r e l i a b l e structure d e t e r m i n a t i o n s a v a i l a b l e of

Pt(II)

chloroammines.

The

P t - N distances

are

2.03(4)Av.,

whereas the P t - C l distances are 2 . 3 2 ( 1 ) A v . a n d are not s i g n i f i c a n t l y d i f ­ ferent i n the t w o isomers. E s s e n t i a l l y the same results for Pt—Ν distances were found i n fram-bis (dimethylamine) diamine platinum (II) Recent

(3).

structures c o n t a i n i n g P t - N distances

methyl-3-butanone-oximato) platinum (II) and bis(glyoximato)platinum(II)

chloride

are

chloride

bis(2-amino-2-

monohydrate

(64)

T h e r e is l i t t l e d o u b t a b o u t the

(23).

b o n d l e n g t h e n i n g that occurs for P t - X trans to h y d r i d e , as has b e e n s h o w n i n P t [ P ( C H ) ] H B r (56) 6

5

3

2

a n d P t [ P ( C H 5 ) C H ] ( H ) C l (20), 6

2

2

5

where

2

the l e n g t h e n i n g is a p p r o x i m a t e l y 0.1A i n b o t h cases. T u r n i n g to other l i g a n d s that h a v e strong trans influence, the struc­ t u r e of

dichlorodi(o-phenylenebisdimethylarsine)platinum(II)

(74)

w h i c h is " s q u a r e p l a n a r " w i t h P t - A s b o n d s of 2 . 3 7 ( 1 ) A is c o n s i d e r a b l y shorter t h a n t h e 2.49A ( 5 7 )

e x p e c t e d f r o m the s u m of s i n g l e - b o n d r a d i i .

U n f o r t u n a t e l y , there are no structure d a t a o n c i s - P t C l ( A s R ) 2

3

for

2

p a r i s o n purposes, b u t the b r i d g i n g c h l o r i n e trans to A s ( C H ) 3

3

com­ has a

P t - C l distance i n d i - M - c h l o r o - [ d i c h l o r o - b i s ( t r i m e t h y l a r s i n e ) ] p l a t i n u m ( I I ) l o n g e r at 2.39A t h a n the b r i d g i n g c h l o r i n e P t - C l d i s t a n c e trans to C I at 2.31A.

T h e P t - A s d i s t a n c e is c o n c o m m i t a n t l y 2.31A ( s o m e w h a t shorter

t h a n for the A s - P t - A s i n t e r a c t i o n ) .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

9.

Crystal

A M M A

Figure

3.

Structure

The

of

127

Complexes

local environment

cis-[(p-C/-C HJ 6

2

·

about the Pt atom in

S] PtCl 2

2

Bond length errors are: Pt-S — Pt-Cl ± 0.007A, S - C = C-C = ±0.02A. Angle errors are ±0.6° or less. S-C distances are not significantly different from 1.80A.

S u l f u r is g e n e r a l l y c o n s i d e r e d as h a v i n g w e a k e r trans influence t h a n p h o s p h i n e s ; h o w e v e r , t h i o u r e a has a greater trans influence t h a n t h i o ether. V e r y f e w structures of P t or P d t h i o e t h e r complexes h a v e b e e n solved. W o o d w a r d et al. (28, 62) h a v e s h o w n that i n ( R S ) M B r w h e n 2

2

2

4

M is P t , the c o m p l e x is a s u l f u r - b r i d g e d d i m e r w i t h r e l a t i v e l y short P t - S b r i d g i n g distances at 2 . 2 0 9 ( 7 ) a n d 2 . 2 4 2 ( 1 4 ) A , a n d P t - B r t e r m i n a l d i s tances of 2 . 3 8 4 ( 4 ) A a n d 2 . 4 0 0 ( 7 ) A . W h e n M is P d , X =

B r , the c o m p l e x

is a trans B r - b r i d g e d d i m e r w i t h P d - B r b r i d g i n g distances of and 2.447(11)A,

2.429(4)A

P d - B r t e r m i n a l distances of 2 . 4 0 4 ( 4 ) A , a n d P d - S d i s -

tances of 2 . 3 0 ( 2 ) A .

I n t e r e s t i n g as the contrast i n these t w o structures

m a y be, t h e y say little a b o u t the trans influence of the P t - S b o n d o n the P t - X b o n d l e n g t h . I n p a r t to e x a m i n e this q u e s t i o n , w e h a v e s o l v e d the structure of d i c h l o r o b i s ( 4 , 4 ' - d i c h l o r o d i p h e n y l s u l f i d e ) p l a t i n u m ( I I )

(70)

( F i g u r e 3 ) . T h e 2S, 2C1, a n d P t atoms are essentially i n the same p l a n e , a n d the P t S C l 2

2

u n i t m a y b e d e s c r i b e d as "square p l a n a r . " T h e P t - C l

distances are n o r m a l single b o n d s , as are the P t - S distances. T h e r e is n o e l o n g a t i o n of the P t - C l distances o w i n g to a trans thioether. T h e P t - S l e n g t h is o n l y s l i g h t l y shorter t h a n the 2.35A expected f r o m the s u m of the c o v a l e n t r a d i i . T h e C - S - P t angles are s u c h that it is clear that S

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

sp

s

128

PLATINUM

orbitals a r e u s e d to f o r m t h e P t - S b o n d .

GROUP

METALS

AND

COMPOUNDS

F u r t h e r , t h e o r i e n t a t i o n of t h e

p - c h l o r o p h e n y l r i n g s is s u c h t h a t n o significant ir i n t e r a c t i o n exists b e ­ t w e e n t h e rings a n d the s u l f u r or P t atoms.

H e n c e , t h e trans influence

of a thioether is n o t reflected i n a n y P t - C l b o n d e l o n g a t i o n . A means o f testing f o r t h e influence of ττ-type interactions i n P t - S b o n d s w o u l d b e t o use a l i g a n d w i t h a geometry that c a n b e p r e c i s e l y l o c a t e d r e l a t i v e t o t h e m e t a l , a n d t h e l o c a t i o n of t h e π orbitals i n this l i g a n d is u n a m b i g u o u s . A l i g a n d that fulfills these c r i t e r i a is t h i o u r e a ( t u ) ; t h e m o l e c u l e is p l a n a r i n a l l k n o w n complexes w i t h metals, a n d t h e π o r b i t a l s a r e n o r m a l to t h e molecular plane.

F u r t h e r , t h e r e l a t i v e energies of t h e ir levels i n this

m o l e c u l e h a v e b e e n c a l c u l a t e d . A s i m p l e M O c a l c u l a t i o n of t h e energy levels

gives

a strongly b o n d i n g

α ι ( — 2.23/3), m o d e r a t e l y

bonding &i

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

(—1.50)8), w e a k l y b o n d i n g d i ( — 0.81/3), a n d s t r o n g l y a n t i b o n d i n g α / ' ( + 1.03/3) ( 2 ) . W i t h six electrons ( o n e electron f r o m S, C., a n d t w o f r o m

Figure 4. (NH ) ^ Cl 2 2

Jt

2

The molecular structure of Pd[SCshowing the principal interatomic dis­ tances

Bond length errors are: Pd-S = Pd-Cl ± 0.003A, S-C ± 0.011 A, C-N ± 0.014A. For clarity the angles are omitted. The angles are: S-Pd-S approximately 90° with errors of 0.Γ, Pd-S-C <-< 110° with errors of 0.4°, S-C-N ~ 120° with errors of Γ or less. N-C-N ~> 120° with errors of 1° or less.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

9.

Crystal

A M M A

Structure

of

129

Complexes

e a c h N ) , these levels are filled t h r o u g h a J . A l t h o u g h this m o l e c u l e c a n b e h a v e as a π d o n o r (69, 72, 78, 79, 81) w i t h o u t s i g m a b o n d i n g , i t has b e e n s h o w n b y others (14, 25, 26, 38, 40, 61) as w e l l as ourselves (8, 54, 55, 84) that, i n g e n e r a l , i t forms b o n d s w i t h t r a n s i t i o n metals via t h e sp

2

orbitals of sulfur. S t e r i c a l l y , i t is possible t o construct a m o d e l s u c h t h a t a l l f o u r t h i o u r e a groups are c o p l a n a r w i t h t h e m e t a l — i . e . , w i t h C

sym­

4h

metry.

A l t h o u g h w e h a v e d e t a i l e d x-ray s t r u c t u r e d a t a o n P t t u C l , 4

Pdtu Cl 4

(8), N i t u C l

2

4

2

(38), C o t u C l 4

(54, 55), a n d N i t u B r

2

6

g e n e r a l i m p o r t a n t features c a n b e seen f r o m P d t u C l 4

Pdtu

4

2

2

2

(84), t h e

( F i g u r e 4). T h e

u n i t is n o t p l a n a r , b u t r a t h e r t h e m e t a l ( n e g l e c t i n g t h e C I a t o m s )

2 +

defines a n a p p r o x i m a t e m o l e c u l a r center of s y m m e t r y a n d t h e t h i o u r e a groups are t i p p e d r e l a t i v e to t h e a p p r o x i m a t e P d S

4

plane b y 43°-60°

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

a n d t w i s t e d r e l a t i v e to t h e P d - S - C fines b y 1 7 ° - 2 6 ° . T h e tilt is d e f i n e d as t h e d i h e d r a l a n g l e b e t w e e n planes—e.g., P d S ( l ) , S ( 3 ) a n d S ( l ) , S(3), C ( l ) . T h e t w i s t is defined as t h e d i h e d r a l angle b e t w e e n p l a n e s — e.g., P d S ( l ) , C ( l ) a n d S ( l ) , C ( l ) , N ( l ) , N ( 2 ) . I t is t e m p t i n g to say that these orientations are g o v e r n e d b y h y d r o g e n b o n d i n g a n d p a c k i n g considerations. H o w e v e r , a p p r o x i m a t e l y t h e same orientations are f o u n d for t h e t h i o u r e a groups i n d e p e n d e n t of m e t a l c o o r d i n a t i o n n u m b e r a n d a n i o n . I n l i e u of a c o m p l e t e d e s c r i p t i o n of t h e electronic structure of t h e c o m p l e x , a possible b u t n o t u n i q u e i n t e r p r e t a t i o n of these results is t h a t i t is e n e r g e t i c a l l y too expensive to r e m o v e electrons f r o m t h e m e t a l dir orbitals to t h e t u π α / ' M O . T h e system distorts ( t i l t s a n d t w i s t s ) i n o r d e r to m a k e use of e m p t y n o n b o n d i n g 3d orbitals o n t h e s u l f u r a t o m . A

f u r t h e r test of this h y p o t h e s i s c a n b e m a d e b y c h a n g i n g t h e

e n e r g y levels of t h e l i g a n d b y , e.g., g o i n g to t h i o a c e t a m i d e ( t a c ) w i t h three π levels at energies (—1.96/3), (—0.91/?), a n d (+0.86/3). I n a s i m i ­ lar m a n n e r , t h e ττ* l e v e l of t h i o u r e a m a y b e m a d e m o r e accessible b y replacing hydrogen dimethylthiourea Ni(DMT) Br 4

Pd(tu)

4

2 +

2

atoms

(DMT).

b y electron donor

substituents, e.g.,

T h e c r y s t a l structures of

Nitac Br 4

sym2

and

h a v e i n d e e d s i g n i f i c a n t l y different s t r u c t u r a l features f r o m

, a n d these differences c a n b e r e l a t e d t o the d i s c u s s i o n above.

Structures

of Delocalized

π-Systems

Involving

Pt

Metals

M u c h interest has b e e n generated i n v a r i o u s properties of m e t a l d e r i v a t i v e s of d i t h i o k e t o n e s , e t h y l e n e (1,2) p o u n d s i n recent years (17,18,29,

facets of these f a s c i n a t i n g c o m p o u n d s , references

dithiolates, a n d related com­

43, 65, 66).

cover t h e m i n some d e t a i l .

T h e r e are m a n y i n t e r e s t i n g

a n d the previously mentioned W e l i m i t ourselves here to t h e

structures of t h e P t g r o u p metajs of these engrossing l i g a n d s .

Unfortu­

n a t e l y , some of t h e m o r e i n t e r e s t i n g p r o p e r t i e s of t h e t r a n s i t i o n metals

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

130

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PLATINUM

Table I.

GROUP

Pd(dtb)

2

L i g a n d charge C h a i r angle M a x i m u m deviation from planarity Distances a. I n t e r l i g a n d S - S b. I n t r a l i g a n d S - S c. M e t a l - S 6

d

e. C - N

AND

COMPOUNDS

Comparison of the Structural

Function

d. S - C

METALS

Ni(dtb)

2

-1 38°

-1 11°

0.51A

0.26A

3.169(2) 3.319(2) 2.301(1) 2.288(1) 1.712(7) 1.743(7) 1.32(1) 1.34(1) 1.35(1)

2.895(6) 3.220(6) 2.160(2) 2.171(2) 1.720(8) 1.728(8) 1.32(1) 1.34(1) 1.34(1)

° T i l t : Angle between planes defined by: M , S(l), S(2) and S(l), C ( l ) , C ( l ) or M , (S(2),C(2). Chair Angle: Angle between planes defined by M , S(l), S(2) and S(l), S(2), N(3). b

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

9.

A M M A

Crystal

Structure

of

131

Complexes

w i t h these l i g a n d s are not m a n i f e s t e d w i t h t h e P t metals. It has b e e n s h o w n t h a t the structures:

η

are c o m p l e t e l y p l a n a r f o r R = M =

N i ,η =

C H , M = 6

6

Ni, η =

0 (63); R =

- 2 ( 1 9 ) ; R — C N , M — N i , η — - 1 (24).

a c c e p t e d that for M =

CN,

It is generaUy

P t , P d , they are i s o s t r u c t u r a l w i t h the N i a n a l o g .

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

F u r t h e r , i t has b e e n s h o w n that e x p a n s i o n of the chelate r i n g also y i e l d s planar

structures,

Co(II)

(6).

for

example,

bis(dithioacetylacetone)Ni(II)

W e d e c i d e d to e x a m i n e w h a t h a p p e n s s t r u c t u r a l l y to the

and

complex

u p o n g o i n g to a s i x - m e m b e r e d r i n g a n d i n a d d i t i o n , a d d i n g a n excess of n o n b o n d i n g π electrons f r o m a p l a n a r l i g a n d . P r e s u m a b l y , the e x p a n s i o n to a s i x - m e m b e r e d r i n g does not effect the p l a n a r i t y , b u t t h e a d d i t i o n of π electrons m i g h t . W e chose the l i g a n d d i t h i o b i u r e t ( H N C S N H C S N H ) . 2

2

W e f o u n d that this l i g a n d reacts as a negative a n i o n w i t h loss of the p r o t o n f r o m the c e n t r a l n i t r o g e n , f o r m i n g n e u t r a l complexes

M(dtb)

2

w i t h P d , P t , a n d N i . T h i s l i g a n d has four m o r e π electrons t h a n does

Parameters of N i ( d t b ) Functions Tilt" Twist

c

Angles a. M - S - C b. S - M - S (Interligand) c. S - C - N (Interior) d. C - N - C

2

and

Pd(dtb)

Pd(dtb)

2

41.1° 30.1° 32.2° 4.4°

2

Ni(dtb)

2

3.23° 18.6° 23.4° 12.4°

108.8(2) 111.6(2) 87.4(1)

116.4(2) 115.3(2) 83.9(1)

131.1(5) 131.3(5) 126.0(6)

130.8(7) 130.2(7) 125.0(8)

Twist: Angle between planes defined by: M , S(l), C ( l ) and S(l), C ( l ) N ( l ) , Ν ( 3 ) ; M , S(2), C(2) and S(2), C(2) Ν(2) N(3). The S(l), C ( l ) , N ( l ) , Ν(3) and S(2), C(2), Ν(2), Ν(3) units are rigorously planar. c

d

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

132

PLATINUM GROUP METALS AND COMPOUNDS

dithioacetylacetone. We have determined the crystal structures of these three complexes (27, 39). The structure of the Pd(dtb) is shown in Figure 5. Although the Ni, Pt, and Pd structures are similar, there are nevertheless some important differences; these are summarized in Table I. In each case, the metal and its four sulfur atoms are planar, but the entire molecule is distinctly not planar; in fact, it is in a chair form. In changing the metal from Pd to Ni, the molecule becomes more planar. If nonbonded repulsions between the sulfur atoms on opposite ligands were responsible for the nonplanarity, it would be expected that the Ni complex would be less planar because the shorter Ni-S distance pulls the nonbonded sulfur atoms closer together. This is clearly not the case. The Pd, Pt complexes could be more distorted from planarity because of steric strain introduced into the six-membered ring by the longer (Pd)Pt-S distances. Alternatively, the distortion could arise from the fact that the extra π electrons on the nitrogen would go into antibonding MO's if the entire molecule were planar and since, in general, there is more metal-ligand π interaction with Pd or Pt than Ni, it would be expfected that these two complexes would be less planar. Another ex­ planation that might be advanced for this change in geometry is that the action of pulling the sulfur atoms closer together brings about some bonded S-S interaction. However, this type of interaction has not been proven as a stabilization factor. This S-S interaction has been suggested (67, 75) as the reason for trigonal prismatic coordination in M(S C R )a (21, 22, 68). Even though there seems to be a S-S ir—π interaction between the individual S C R groups, this interaction alone would not stabilize trigonal prismatic coordination so long as the ligands are neutral or dianions.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

2

2

2

2

2

2

2

Acknowledgment The authors receivedfinancialsupport from National Institutes of Health, Grants GM-13985 and HE-12523. Literature Cited (1) Albano, V. G., Ricci, G. M. B., Bellon, P. L., Inorg. Chem. 1969, 8, 2109. (2) Amma, E. L., unpublished calculations. (3) Anderson, J. S., Carmichael, J. W., Cordes, A. W., Inorg. Chem. 1970, 9, 143. (4) Baenziger, N.C.,Medrud, R.C.,Doyle, J. R., Acta Cryst. 1965, 18, 237. (5) Basolo, F., Pearson, R. G., "Mechanisms of Inorganic Reactions," 2nd ed., a) p. 355, b) p. 360, Wiley, New York, 1967. (6) Beckett, R., Hoskins, B. F., Chem. Commun. 1967, 909. (7) Bentley, G. Α., Laing, Κ. R., Roper, W. R., Waters, J. M., Chem. Com­ mun. 1970, 998.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

9. AMMA

Crystal Structure of Complexes

133

(8) Berta, D. Α., Spofford, W. Α.,III,Boldrini, P., Amma, E. L., Inorg. Chem. 1970, 9, 136. (9) Black, M., Mais, R. H. B., Owston, P. G., Acta Cryst. 1969, B25, 1753. (10) Ibid., 1969, B25, 1760. (11) Bokii, G. B., Kukina, G. Α., Zh. Strukt. Khim. 1965, 5, 706. (12) Bombieri, G., Forsellini, E., Panattoni, G., Graziani, R., Bandoli, G., J. Chem. Soc. 1970, A 1313. (13) Bottomley, F., Nyburg, S. C., Chem. Commun. 1966, 897. (14) Capacchi, L., Gasparri, G. F., Nardelli, M., Pelizzi, G., Acta Cryst. 1968, B24, 1199. (15) Davis, B. R., Ibers, J. Α., Am. Cryst. Assoc. Meeting, New Orleans, La March 1970, Abstr. No. C-9; Inorg. Chem. 1970, 9, 2768. (16) Davis, B. R., Payne, N. C., Ibers, J. Α., Inorg. Chem. 1969, 8, 2719. (17) Davison, Α., Edelstein, N., Holm, R. H., Maki, A. H., J. Am. Chem. Soc. 1963, 85, 2029. (18) Ibid., 1964, 86, 2799. (19) Eisenberg, R., Ibers, J. Α., Inorg. Chem. 1965, 4, 605. (20) Ibid., 1965, 4, 773. (21) Eisenberg, R., Ibers, J. Α.,J.Am. Chem. Soc. 1965, 87, 3776. (22) Eisenberg, R., Stiefel, Ε. I., Rosenberg, R. C., Gray, Η. B., J. Am. Chem. Soc. 1966, 88, 2874. (23) Ferraris, G., Viterbo, D., Acta Cryst. 1969, B25, 2066. (24) Fritchie, C. J., Jr., Acta Cryst. 1966, 20, 107. (25) Gasparri, G. F., Mangia, Α., Musatti, Α., Nardelli, M., Acta Cryst. 1969, B25, 203. (26) Gasparri, G. F., Musatti, Α., Nardelli, M., Chem. Commun. 1966, 602. (27) Girling, R. L., Amma, E. L., Chem. Commun. 1968, 1487. (28) Goggin, P. L., Goodfellow, R. J., Sales, D. L., Stokes, J., Woodward, P., Chem. Commun. 1968, 31. (29) Gray, H. B., Trans. Metal Chem. 1965, 1, 239. (30) Hodgson, D. J., Ibers, J. Α., Inorg. Chem. 1968, 7, 2345. (31) Ibid., 1969, 8, 1282. (32) Hodgson, D. J., Payne, N. C., McGinnety, J. Α., Pearson, R. G., Ibers, J. Α., J. Am. Chem. Soc. 1968, 90, 4486. (33) Jarvis, J. A. J., Kilbourn, B. T., Owston, P. G., Acta Cryst. 1970, B26, 876. (34) Kashiwagi, T., Yasuoka, N., Kasai, N., Kakudo, M., Takahashi, S., Hagi­ hara, N., Chem. Commun. 1969, 743. (35) Langford, C. H., Gray, H. B., "Ligand Substitution Processes," Benjamin, New York, 1966. (36) La Placa, S. J., Ibers, J. Α., Inorg. Chem. 1966, 5, 405. (37) La Placa, S. J., Ibers, J. Α., J. Am. Chem. Soc. 1965, 87, 2581. (38) Lopez-Castro, Α., Truter, M. R., J. Chem. Soc. 1963, 1309. (39) Luth, H., Hall, Ε. Α., Spofford, W. Α., III, Amma, E. L., Chem. Com­ mun. 1969, 520. (40) Luth, H., Truter, M. R., J. Chem. Soc. 1968, A, 1879. (41) Mais, R. H. B., Owston, P. G., Wood, A. M., unpublished results, 1968. (42) Mason, R., Rae, Α. I. M., J. Chem. Soc. 1970, 1767. (43) McCleverty, J. Α., Progr. Inorg. Chem. 1968, 10, 49. (44) McGinnety, J. Α., Doedens, R. J., Ibers, J. Α., Inorg. Chem. 1967, 6, 2243. (45) McGinnety, J. Α., Ibers, J. Α., Chem. Commun. 1968, 235. (46) McGinnety, J. Α., Payne, N. C., Ibers, J. Α.,J.Am. Chem. Soc. 1969, 91, 6301. (47) Mellor, D. P., Wunderlich, J. Α., Acta Cryst. 1954, 7, 130. (48) Ibid., 1955, 8, 57. (49) Messmer, G. G., Amma, E. L., Inorg. Chem. 1966, 5, 1775. (50) Messmer, G. G., Amma, E. L., Ibers, J. Α., Inorg. Chem. 1967, 6, 725. (51) Milburn, G. H. W., Truter, M. R., J. Chem. Soc. 1966, A, 1609.

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Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

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(52) (53) (54) (55) (56) (57) (58) (59) (60) (61) (62) (63) (64) (65) (66) (67) (68) (69) (70) (71) (72) (73) (74) (75) (76)

Mingos, D. M. P., Ibers, J. Α., Inorg. Chem. 1970, 9, 1105. Muir, K. W., Ibers, J. Α., Inorg. Chem. 1969, 8, 1921. O'Connor, J. E., Amma, E. L., Chem. Commun. 1968, 892. O'Connor, J. E., Amma, E. L., Inorg. Chem. 1969, 8, 2367. Owston, P. G., Partridge, J. M., Rowe, J. M., Acta Cryst. 1960, 13, 246. Pauling, L., "Nature of the Chemical Bond," 3rded.,p. 249, Cornell Uni­ versity Press, 1960. Payne, N.C.,Ibers, J. Α., Inorg. Chem. 1969, 8, 2714. Pierpont, C. G., Van Derveer, D. G., Durlard, W., Eisenberg, R., J. Am. Chem. Soc. 1970, 92, 4760. Ricci, J. S., Ibers, J. Α., Fraser, M. S., Baddley, W. H., J. Am. Chem. Soc. 1970, 92, 3489. Robinson, W. T., Holt, S. L., Jr., Carpenter, G. B., Inorg. Chem. 1967, 6, 605. Sales, D. L., Stokes, J., Woodward, P.,J.Chem. Soc. 1968, A, 1852. Sartain, D., Truter, M. R., Chem. Commun. 1966, 382;J.Chem. Soc. A 1967, 1264. Schlemper, E. O., Inorg. Chem. 1969, 8, 2740. Schrauzer, G. N., Acct. Chem. Res. 1969, 2, 72. Schrauzer, G. N., Trans. Metal Chem. 1968, 4, 299. Schrauzer, G. N., Mayweg, V. P.,J.Am. Chem. Soc. 1966, 88, 3235. Smith, A. E., Schrauzer, G. N., Mayweg, B. P., Heinrich, W.,J.Am. Chem. Soc. 1965, 87, 5798. Spofford, W. Α.,III,Amma, E. L., Chem. Commun. 1968, 405. Spofford, W. Α.,III,Amma, E. L., Natl. Mtg. ACS, 157th, Minneapoli Minnesota, April 1969, Abstr. INOR 133; Inorg. Chem., in press. Spofford, W. Α.,III,Amma, E. L., to be published. Spofford, W. Α.,III,Boldrini, P., Amma, E. L., Carfagno, P., Gentile, P. S., Chem. Commun. 1970, 40. Stalick, J. K., Ibers, J. Α., Inorg. Chem. 1969, 8, 419. Stephenson, N.C.,Acta Cryst. 1964, 17, 1517. Stiefel, E.I.,Eisenberg, R., Rosenberg, R.C.,Gray, H. B.,J.Am. Chem. Soc. 1966, 88, 2956. Sutton, L. E., Ed., "Tables of Inter-Atomic Distances and Configuration in Molecules and Ions," Supplement, 1956-59, Special Publication No. 18, p. S-9-s, The Chemical Society, London, 1965. (77) Taylor, I. F., Jr., Weininger, M. S., Amma, E. L., to be published. (78) Vizzini, Ε. Α., Amma, E. L., J. Am. Chem. Soc. 1966, 88, 2872. (79) Vizzini, Ε. Α., Taylor, I. F., Jr., Amma, E. L., Inorg. Chem. 1968, 7, 1351. (80) Vogt, L. H., Jr., Katz, J. L., Wiberly, S. E., Inorg. Chem. 1965, 4, 1157. (81) Vranka, R. G., Amma, E. L., J. Am. Chem. Soc. 1966, 88, 4270. (82) Watkins, S. F., Chem. Commun. 1968, 504. (83) Watkins, S. F., J. Chem. Soc. 1970, A, 168. (84) Weininger, M. S., O'Connor, J. E., Amma, E. L., Inorg. Chem. 1969, 8, 424. (85) Zumdahl, S. S., Drago, R. S.,J.Am. Chem. Soc. 1968, 90, 6669. RECEIVED February 18, 1970.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10

195

Pt—A

Survey of Mossbauer Spectroscopy

N. BENCZER-KOLLER Department of Physics, Rutgers University, New Brunswick, N. J. 08903

The recoilless resonance absorption and scattering of the 99 keV transition in Pthas been studied to determine the lifetime [τ = (1.7 ± 0.2) χ 10 sec], conversion coeffi­ cient (α= 7.0 ± 0.3), magnetic moment (μ = —0.615 ± 0.041 nm), and radius relative to the ground state radiu ( δ R / R <0)of thefirstexcited state of Pt.The magnetic hyperfine structure of iron, cobalt, and nickel alloys was investigated. The internalfieldat the platinum nucleus in all these alloys was negative, and its magnitude suggest that its main contribution comes from polarization of con­ duction electrons. The temperature dependence of the Debye-Waller factor is in excellent agreement with predic­ tions based on the quasiharmonic model.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

195

-10

195

An interesting candidate for Mossbauer effect studies from the point of view of both nuclear structure and solid state investigations is Pt. Au decays to Pt (10) (Figure 1) with a half-life of 192 days, and feeds two states at 99 and 130 keV, respectively, both of which in prin­ ciple may be used for recoilless resonance experiments. However, both states have short mean lives and therefore relatively broad resonance lines. In addition, because of the high energy of the transitions, the recoilless fraction is small. Most of the results described below have been obtained from the study of the Mossbauer effect of the 99 keV transition alone. The mean life of the 99 keVfirstexcited state, its magnetic moment, and the internal conversion coefficient α of the radiative transition are the nuclear properties of the state that were determined by Mossbauer spec­ troscopy. The interest in the solid state properties of platinum metal lies in the fact that magnetic properties of platinum alloys are nearly un­ known compared with those of the iron group metals and alloys. Fur­ thermore, the study of platinum metal lattice dynamics is amenable to straightforward theoretical analysis because of the simple crystal struc195

195

195

135 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

136

PLATINUM

METALS

AND

COMPOUNDS

195m Ptni =4.ld)

keV

re

/2

259.3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

GROUP

13/2+

Physical Review

Figure 1. Decay scheme of Au and energy level diagram of Pt ( 1 0 ) . P i represents the relative transition probability for electron cap­ ture decay to the state i in Pt and P i / P j is the ratio of Κ to total capture for decay to the state i . 195

195

K

195

1

1

1

1

1

1

1

1

b>

r

ι

Ta=Ts=20°K ta=0.0063 in.

1.00 J99 .98

\\ J f

J97 36 .95 .94

€= «052*.002 -5

-4

-3

-2

- 1 0 1 2

3

4

5

RELATIVE VELOCITY CM/SEC)

Physical Review

Figure 2. Typical Mossbauer absorption spec­ trum obtained with a Au in a Pt matrix source and a 0.0063-inch thick Pt absorber; both source and absorber were at 20°Κ (9) 195

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10.

BENCZER-KOLLER:

Survey of Mossbauer

137

Spectroscopy

ture a n d vast a v a i l a b l e d a t a o n heat capacity, lattice constants, a n d elastic constants.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

I n a b a s i c M o s s b a u e r e x p e r i m e n t , the r e d u c t i o n i n t r a n s m i s s i o n ( 9 ) ( F i g u r e 2 ) or the increase i n scattered i n t e n s i t y of r a d i a t i o n ( 2 ) ( F i g u r e 3 ) is o b s e r v e d as a f u n c t i o n of the r e l a t i v e v e l o c i t y b e t w e e n a source a n d an absorber. T h e f u l l w i d t h at h a l f m a x i m u m of the resonance c u r v e Γ is r e l a t e d to the m e a n l i f e of the r a d i a t i n g state b y the u n c e r t a i n t y r e l a ­ tion Γ 2fr/r. T h e d e p t h of the c u r v e , C., is r e l a t e d to / , t h e m a g n i t u d e of the recoilless f r a c t i o n of g a m m a rays e m i t t e d , a n d h e n c e to the c r y s ­ t a l l i n e properties of the s o l i d . F i n a l l y , the d i s p l a c e m e n t of the c u r v e f r o m zero r e l a t i v e v e l o c i t y indicates the e n e r g y difference b e t w e e n e m i t t e d a n d a b s o r b e d r a d i a t i o n a n d is p r o p o r t i o n a l to the s-electron

τ

I

I

I

I

Γ

Physics Letters

Figure 3. Typical Mossbauer scattering spectrum obtained with 32 mg/cm Pt scatterer at 29°Κ and 560 mg/cm Pt scatterer at 92°Κ (2)

2

2

d e n s i t y difference at the nucleus i n the source a n d absorber, a n d to the difference i n the m e a n square r a d i u s of the nucleus i n its e x c i t e d state and its g r o u n d state.

Resonance Effect and Line Width of the 99 and 130 keV Transitions T h e 99 k e V S t a t e . T y p i c a l l y , a source of 1-3 m C i of p l a t e d o n a p l a t i n u m f o i l m a y be used.

1 9 5

A u electro­

T h e resonance effect for the

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

138

PLATINUM

GROUP

METALS

AND

COMPOUNDS

99 k e V t r a n s i t i o n f o r s u c h a source a n d a 0.006-inch n a t u r a l p l a t i n u m f o i l absorber, b o t h at 20 °K, is c Ξ== 5% a n d the l i n e w i d t h Γ = 2.1 c m / s e c . T h e w i d t h of the resonant l i n e depends o n the absorber thickness, t . T h e a

e x t r a p o l a t e d l i n e w i d t h at t = 0, Γ = a

h a l f l i f e of t h e state, τ

1 / 2

=

(1.7 ±

(1.75 ± 0.18) c m / s e c , y i e l d s t h e

0.2) Χ 10"

10

sec, i f one assumes n o

b r o a d e n i n g of t h e l i n e o w i n g to hyperfine interactions. T h i s v a l u e agrees w i t h the electronically measured value r

1/2

«

1.4 Χ 10"

10

sec (4). A s

p l a t i n u m m e t a l is a c u b i c c r y s t a l , n o l i n e b r o a d e n i n g interactions are e x p e c t e d (9). T h e 130 k e V S t a t e . T h e d e c a y of the 130 k e V state has b e e n s t u d i e d extensively, a n d several inconsistencies a r e b e i n g r e s o l v e d .

T h e results

of different measurements of t h e m e a n l i f e a n d d e c a y m o d e of t h e 130 Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

k e V state a r e discussed b y F i n k a n d B e n c z e r - K o l l e r (8).

T h e half-life

of t h e state has b e e n m e a s u r e d e l e c t r o n i c a l l y , a n d t h e t r a n s i t i o n m a t r i x e l e m e n t for excitation has b e e n d e r i v e d f r o m C o u l o m b e x c i t a t i o n d a t a T h e c o m b i n a t i o n of t h e C o u l o m b e x c i t a t i o n y i e l d , t h e i n t e r n a l

(12).

c o n v e r s i o n coefficient (8) a =

1.76 ± 0.19, a n d t h e b r a n c h i n g r a t i o

(8)

P o = 0.060 ± 0.008 f o r t h e crossover d e c a y to g r o u n d , y i e l d s a h a l f - l i f e C

τι/2 =

0.014) ns i n excellent agreement w i t h a recent

(0.414 ±

M o s s b a u e r d e t e r m i n a t i o n of t h e l i n e w i d t h , Γ = e q u i v a l e n t to π /

2

=

(4.4 ±

(0.49 ± 0.05) ns. W i l e n z i c k et al. (15)

(15)

mm/sec,

0.4)

do not i n ­

d i c a t e t h e thickness of t h e P t absorber u s e d . T h e resonance l i n e f r o m t h e 130 k e V state is a factor of 5 n a r r o w e r t h a n that f r o m t h e 99 k e V t r a n s i t i o n a n d therefore m o r e a m e n a b l e to i s o m e r shift studies. recoilfree f r a c t i o n , / =

H o w e v e r , e v e n at 20°K, t h e 130 k e V t r a n s i t i o n 2.8%, is m u c h s m a l l e r t h a n that of t h e 99 k e V

t r a n s i t i o n , a n d t h e effect o b s e r v e d 0.26%

w i t h a 0.011-inch absorber is o n l y

(10).

Lattice Dynamics T w o of t h e m o r e d i r e c t t e c h n i q u e s u s e d i n t h e s t u d y o f l a t t i c e d y ­ n a m i c s of crystals h a v e b e e n t h e s c a t t e r i n g of neutrons a n d of x-rays f r o m crystals. I n a d d i t i o n , t h e p h o n o n v i b r a t i o n a l s p e c t r u m c a n b e i n ­ f e r r e d f r o m c a r e f u l analysis of measurements of specific heat a n d elastic constants.

I n studies of B r a g g reflection of x-rays ( w h i c h i n v o l v e s n o

loss of energy t o t h e l a t t i c e ) , i t w a s f o u n d that t e m p e r a t u r e has a strong influence o n t h e i n t e n s i t y of t h e reflected lines.

T h e i n t e n s i t y of the

scattered x-rays as a f u n c t i o n of t e m p e r a t u r e c a n b e expressed b y =

I e~ 0

2wm

w h e r e 2W(T)

is c a l l e d t h e D e b y e - W a l l e r factor.

I(T)

Similarly;

i n t h e M o s s b a u e r effect, g a m m a rays are e m i t t e d or a b s o r b e d

without

loss o f energy a n d w i t h o u t change i n t h e q u a n t u m state of t h e lattice b y

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10.

BENCZER-KOLLER

Survey

of Mossbauer

139

Spectroscopy

a n u c l e u s b o u n d i n a c r y s t a l . T h e f r a c t i o n / of recoilless g a m m a rays e m i t t e d or a b s o r b e d b y a n u c l e u s i n a c r y s t a l l a t t i c e is e~

2W

w h e r e R = r e c o i l e n e r g y of n u c l e u s a n d G (ω) =

where

frequency distribution,

n o r m a l i z e d so that

J

G(G>)

άω =

1

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

ο If t h e lattice is a s s u m e d to h a v e a D e b y e f r e q u e n c y s p e c t r u m w i t h c o = k6 /h, then DW

m

where 6

DW

is t h e effective D e b y e t e m p e r a t u r e .

s p e c t r u m , G (ω),

Since t h e r e a l f r e q u e n c y

m a y b e c o n s i d e r a b l y different f r o m a h a r m o n i c

Debye

s p e c t r u m , t h e effective D e b y e t e m p e r a t u r e a p p r o p r i a t e to a n y other q u a n ­ t i t y i n v o l v i n g a different average over t h e s p e c t r u m m a y b e a p p r e c i a b l y different f r o m 6 DW

T h u s , for example, the D e b y e temperature 0 perti­ C

nent to the heat c a p a c i t y w i l l v a r y m u c h m o r e r a p i d l y w i t h t e m p e r a t u r e than 0 . DW

I n p r i n c i p l e , h o w e v e r , f r o m k n o w l e d g e of t h e heat c a p a c i t y ,

lattice constants, a n d elastic constants as a f u n c t i o n of t e m p e r a t u r e , one c a n l e a r n e n o u g h a b o u t the f r e q u e n c y s p e c t r u m to p r e d i c t t h e D e b y e W a l l e r factor.

F e l d m a n a n d H o r t o n ( 7 ) have m a d e s u c h a c a l c u l a t i o n

in the quasiharmonic approximation i n w h i c h the lattice potential i n P t m e t a l is a s s u m e d to b e h a r m o n i c , a n d of a l l a n h a r m o n i c effects, o n l y the

_ 240

^23I°K

229 K>^ e

Ξ 230 ο ®

225 K^^ e

220 210 0

100

50

150

200

250

300 Physical Review

Figure 4. Flot of ^ ( T ) vs. T . The solid line gives the value of ^ D W ( T ) referred to the 0°K volume. The broken line shows the effect of thermal expansion ( 7 ) . D

W

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

140

PLATINUM

t h e r m a l expansion is t a k e n i n t o account. D e b y e temperature should b e 0

DW

=

GROUP

METALS

A N D COMPOUNDS

T h e i r conclusions are that the

(231 ± 3 ) ° K at 0 ° K a n d s h o u l d

have a very slight temperature dependence ( F i g u r e 4 ) . Experimentally, f r o m the analysis of the t e m p e r a t u r e d e p e n d e n c e of the a b s o r p t i o n s p e c t r a o b t a i n e d w i t h a source o f

1 9 5

A u embedded in a natural platinum matrix

a n d a n a t u r a l p l a t i n u m absorber, H a r r i s , R o t h b e r g , a n d B e n c z e r - K o l l e r (JO) obtained an extrapolated 0

DW

=

(234 ± 6 ) ° K at 0 ° K i n excellent

a g r e e m e n t w i t h t h e o r e t i c a l p r e d i c t i o n s f o r the p l a t i n u m c u b i c l a t t i c e . A c t u a l l y , the q u a n t i t y t h a t is m e a s u r e d is f/(l

+ a), n a m e l y a c o m b i n a ­

t i o n o f the recoilless f r a c t i o n / a n d o f the c o n v e r s i o n coefficient « . T h e determination of 6

DW

is t h e n v e r y sensitive to the c h o i c e o f a ( F i g u r e 5 ) .

If the e x p e r i m e n t a l 2 W is fitted to the t h e o r e t i c a l p r e d i c t i o n s o f F e l d m a n Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

a n d H o r t o n , t h e n a v a l u e for the c o n v e r s i o n coefficient a c a n b e o b t a i n e d , a = 7.0 ± 0.3. T h i s v a l u e o f the i n t e r n a l c o n v e r s i o n coefficient is m o r e

β no

K)

2030405060708090100 TfK) Physical Review

Figure 5. Experimental values ( 9 ) of 0 for various values of the internal conversion coefficient vs. temperature. The solid line was obtained from the analysis of specific heat measurements and other thermody­ namic data ( 7 ) . D W

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

B E N C Z E R - K O L L E R

Survey of Mossbauer

141

Spectroscopy

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

10.

Physics Letters

Figure 6.

Mossbauer spectra with Pt in ferromagnetic

alloys

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

(2)

142

GROUP

METALS

AND

COMPOUNDS

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

PLATINUM

Physical Review

Figure

7. Mossbauer spectra for Pt-Fe absorbers in different field configurations (1)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

10.

BENCZER-KOLLER

Survey of Mossbauer

143

Spectroscopy

Physical Review

Figure 8. Mossbauer spectra for absorbers of Pt-Co, Pt-Ni, and Pt (1) precise t h a n t h a t w h i c h c a n b e o b t a i n e d b y a n y of the n u c l e a r spectroscopy m e t h o d s a v a i l a b l e to date.

Hyperfine Interaction T h e M o s s b a u e r a b s o r p t i o n of scattering experiments w e r e c a r r i e d out b y B e n c z e r - K o l l e r , H a r r i s , a n d R o t h b e r g ( 3 ) , A t a c , D e b r u n n e r , a n d F r a u e n f e l d e r (2),

Agresti, Kankeleit, a n d Persson ( J ) , a n d B u y r n , G r o d -

zins, B l u m , a n d W u l f f (6) Pt-Fe

w i t h a single l i n e source a n d absorbers

alloys r a n g i n g i n c o m p o s i t i o n

from

P t - C o , a n d P t - N i alloys as w e l l as P t F e . 3

Pto.03Feo.97 to

of

Pt .5oFe .5o, 0

0

A t y p i c a l s p e c t r u m is s h o w n

i n F i g u r e 6. T h e e x p e c t e d 6-line p a t t e r n c o r r e s p o n d i n g to a 3 / 2 - »

1/2

m a g n e t i c d i p o l e t r a n s i t i o n is not r e s o l v e d , a n d o n l y t w o peaks c a n b e o b served. F r o m a 6-line fit to the o b s e r v e d p a t t e r n , H a r r i s et al. ( 3 )

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

were

144

PLATINUM

Table I.

GROUP

AND

COMPOUNDS

Magnetic Moment of the 99 k e V Excited State in T.,

Absorber

°K

T.,

°K

Pto.iFeo.9 Pt Fe

229 418

20 20

20 20

Pto.sFeo.7 Pto.07Coo.93 Pto.07Nio.93

166 71.5 140

29 29 29

29 29 29

Pto.03Feo.97 Pto.03Coo.97 Pto.03Nio.97

30-60 50 50

4.2 4.2 4.2

4.2 4.2 4.2

Pto.03Feo.97 •

52

4.2

4.2

3

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

METALS

• 521

Pto.50Feo.50

Calorimetric determination P o l a r i z e d n e u t r o n - s p i n resonance

Pto.03Feo.97 Pto.iFeo.9 Average

Table II.

W i d t h , Isomer Shift, Magnitude of the A u in Various Matrices and 1 9 5

(Mv\

t Source Matrix

\Cm2J

Pt

Cu Be Ir Pt 195mp

t

p

m

t

T.,

°K

Foil

326 326 610 104

4.2 4.2 4.2 20.0

4.2 4.2 4.2 20.0

326

4.2

4.2

o n l y a b l e to o b t a i n a r e l a t i o n s h i p b e t w e e n H n u c l e u s , a n d the r a t i o μ*/μ

ΰ

i n t

2.04 ± 0.10 ~2.5 3.05 ± 0.15 2.1 =fc 0.2

, t h e effective field at the

of m a g n e t i c m o m e n t s

of the e x c i t e d

and

g r o u n d states. T h e three o t h e r groups a l t e r e d t h e a b s o r p t i o n or s c a t t e r i n g patterns b y p o l a r i z i n g t h e absorbers w i t h a n e x t e r n a l field a p p l i e d e i t h e r p a r a l l e l or p e r p e n d i c u l a r to the g a m m a r a y e m i s s i o n ( F i g u r e s 7 a n d 8 ) . T h e y thus w e r e able to o b t a i n u n i q u e v a l u e s for the s i g n a n d m a g n i t u d e of μβ a n d H

i n t

.

T h e s e results, as w e l l as i n t e r n a l fields o b t a i n e d f r o m a

c a l o r i m e t r i c d e t e r m i n a t i o n (11)

a n d a p o l a r i z e d n e u t r o n s p i n resonance

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10. 1 9 5

Spectroscopy

145

P t and Internal Magnetic Field for Various P t - F e Alloys

μ

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

Survey of Mossbauer

B E N C Z E R - K O L L E R

Hint MG

β

Ref.

-0.9<μ<0.18

-1.2<#<-2.9 0

3

- 0 . 6 4 5 =fc 0.150

-1.24 -0.77 -0.34

±0.15 ± 0.07 ± 0.08

2

- 0 . 6 1 5 ± 0.045

-1.119 ± 0 . 0 4 - 0 . 8 6 ± 0.03 - 0 . 3 6 ± 0.04

1

- 0 . 5 8 5 ± 0.120

-1.29

6

Hint Hint

±0.09

= 1.39 = 1.08

11 13 1,2 β

- 0 . 6 1 5 ± 0.041

Effect, and Effective Debye Temperature for Sources of N a t u r a l Platinum Absorber ( 6 ) Effect,

%

·(&) 6.2 6.0 11.9 5.2

<0.05 <0.05

θβ, °K 0.3 0.8 1.0 0.2

220 220 315 234

Ref. 5

± 20 ± 30 ± 35 ± 6

-6

e x p e r i m e n t (13) values of H if

i n t

i n t

o n similar alloys, are shown i n T a b l e I. These latter

d o n o t agree too w e l l w i t h t h e M o s s b a u e r effect results.

is s m a l l e r f o r t h e P t - C o a n d P t - N i alloys t h a n f o r t h e P t - F e case. H o w e v e r , the r a t i o of H

i n t

t o t h e effective m a g n e t i c m o m e n t of t h e

host a t o m is a l m o s t constant f o r t h e three a l l o y s , as is to b e e x p e c t e d i f c o n ­ d u c t i o n e l e c t r o n p o l a r i z a t i o n is t h e cause of t h e i n t e r n a l fields. A c c u r a t e t h e o r e t i c a l estimates of t h e c o n t r i b u t i o n s to H

lut

f r o m c o n d u c t i o n elec­

t r o n p o l a r i z a t i o n a n d f r o m core p o l a r i z a t i o n h a v e n o t b e e n m a d e yet.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

146

PLATINUM

GROUP

METALS

AND

COMPOUNDS

Debye Temperatures for Platinum in Pt, Be, Cu, and Ir In most experiments reported, matrices were used.

1 9 5

A u sources e m b e d d e d i n p l a t i n u m

F o r these sources, the recoilless f r a c t i o n , e v e n a t

l i q u i d h e l i u m t e m p e r a t u r e s , is s m a l l , a n d the resonance effects are of t h e o r d e r of a f e w p e r cent at best.

Table III.

T.,

T.,

°K

°K

Pt Pto.iFeo.9 Pto.sFeo.7 Pto.sFeo.ô Pt Fe

217 229 147 216 418

20 20 20 20 20

20 20 20 20

Pt

32 122 580 580

29 29 29 92

29 29 29 92

Pto.03Feo.97 Pto.07Coo.93 Pto.07Nio.93

166 71.5 140

29 29 29

29 29 29

Pt Pto.03Feo.97 Pto.03Coo.97 Pto.03Nio.97 PtO Pt0 PtCl PtCl

50 30-60 50 50

3

s e a r c h e d for

Widths, Isomer Shift, and Mossbauer Fractions

Absorber

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

B u y r n and Grodzins (5)

\SecJ

1.91 1.98 2.14 2.46

0.08 0.07 0.06 0.07

2.05 2.03 2.01

4.2 4.2 4.2 4.2

4.2 4.2 4.2 4.2

± ± ± ±

1.80 1.74 1.86 1.78

db ± ± ±

0.04 0.003 0.004 0.006

2

2

4

Pto.2oAUo.80

e n v i r o n m e n t s for w h i c h a h i g h e r D e b y e t e m p e r a t u r e a n d h e n c e a l a r g e r effect c o u l d be o b t a i n e d .

T h e y u s e d sources of

Be, a n d Ir matrices ( T a b l e I I ) . 6

DW

=

(315 ±

1 9 5

A u and

1 9 5 w i

Pt in Cu,

I r is b y f a r the best host m a t e r i a l , w i t h

3 5 ) ° K , as c o m p a r e d w i t h 6 (Vt)

(234 ±

=

DW

6)°K.

In

a l l cases, the D e b y e - W a l l e r t e m p e r a t u r e 6 w is o n l y i n r o u g h a g r e e m e n t D

w i t h the p r e d i c t e d values 0 ff = e

0host ( M

h o s

t/M

i m

p)

1 / 2

for a n i m p u r i t y

a t o m b o u n d w i t h the same force constant as the host atoms.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10.

Survey of Mossbauer

B E N C Z E R - K O L L E R

147

Spectroscopy

Isomeric Shift A g r e s t i , K a n k e l e i t , a n d Persson ( I )

s t u d i e d the M o s s b a u e r

effect

w i t h alloys of 20 a t o m % P t i n A u a n d 0.7 a t o m % P t i n A l , as w e l l as w i t h c o m p o u n d s s u c h as P t O , P t 0 , P t C l , a n d P t C l 2

2

4

( T a b l e I I I ) i n order

to o b t a i n f u r t h e r i n f o r m a t i o n a b o u t i s o m e r i c shifts a n d p o s s i b l y e l e c t r i c

for Various Ferromagnetic Alloys and Platinum Compounds

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

f 1.70

zb 0.20

-0.16 -0.10 -0.14 -0.12

zb zb zb zb

0.04 0.02 0.07 0.14

-0.21 -0.35 -0.23

zb 0.02 zb 0.03 zb 0.02

-0.006 -0.190 -0.196 -0.165 -0.034 -0.040 -0.010 -0.03 +0.075 -0.205

zb zb zb zb zb zb zb zb zb

f

s

( ) ; 0.089 ± / V

0.002

\ 0.096 =b 0.015 0.02

=b 0.003

0.129 0.269 0.243 0.116 0.096

Ref.

a

db =b ± db db

0.008 0.041 0.026 0.008 0.010

3,9

0.105 =b 0.015 0.02

=b 0.003

0.017 0.011 0.009 0.008 0.011 0.008 0.020 0.03 0.002 db 0.001

q u a d r u p o l a r interactions. T h e y h a v e o b s e r v e d i s o m e r i c shifts ( F i g u r e 9 ) w h i c h decrease w i t h d e c r e a s i n g e l e c t r o n e g a t i v i t y of the host element.

If

d e c r e a s i n g the e l e c t r o n e g a t i v i t y of the host m a t e r i a l reflects a n increase i n the e l e c t r o n d e n s i t y at the i m p u r i t y n u c l e u s , the s i g n of the i s o m e r i c shifts i m p l i e s that the m e a n square radius, for the

1 9 5

P t first e x c i t e d state

is s m a l l e r t h a n t h a t of the g r o u n d state. T h i s result is i n a g r e e m e n t w i t h the p r e d i c t i o n of U h e r a n d Sorensen (14)

for the r e l a t i v e effective r a d i i

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

148

PLATINUM GROUP METALS AND COMPOUNDS

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

Pt-AI 15 .

2.0 ELECTRONEGATIVITY

Physical Reveiw Figure 9. Plot of the isomeric shift of platinum alloys vs. the electronegativity of the host eleme The deviation for Pt-Al from the general trend might occur because the platinum is not in a so solution. In the insert, isomeric shifts for som platinum compounds are shown related to th valency of platinum (1). 195

of Pt nuclei with the valence neutron in the 3p or the 3p states. Both the 99 and 130 keV states exhibit relatively small collective effects [B(E2) ^ 10 W.u.] compared with the higher excited states of Pt, and therefore the root mean square radii should be controlled mostly by the monopole core polarization contribution. Under these circumstances, the isomer shift for the 130 keV state should be vanishingly small, as the effective radii for the 2/ and 3p neutron states are almost equal. 3/2

1/2

195

5/2

V2

Acknowledgment This work was supported by the National Science Foundation. Literature Cited (1) Agresti, D., Kankeleit, E., Persson, B., Phys. Rev. 1967, 155, 1339. (2) Atac, M., Debrunner, P., Frauenfelder, H., Phys. Letters 1966, 21, 699. (3) Benczer-Koller, N., Harris, J. R., Rothberg, G. M., Phys. Rev. 1965, 140, B547. (4) Blaugrund, A. E., Phys. Rev. Letters 1959, 3, 226. (5) Buyrn, A. B., Grodzins, L., Phys. Letters 1966, 21, 389. (6) Buyrn, A. B., Grodzins, L., Blum, Ν. Α., Wulff, J., Phys. Rev. 1967, 163, 286. (7) Feldman, J. L., Horton,G.Κ., Phys. Rev. 1965, 137, A1106.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

10. BENCZER-KOLLER

149 Survey of Mossbauer Spectroscopy

Fink, T., Benczer-Koller, N., Nucl. Phys. 1969, A138, 337. Harris, J. R., Benczer-Koller, N., Rothberg, G. M., Phys. Rev. 1965, 137, A1101. Harris, J. R., Rothberg, G. M., Benczer-Koller, N., Phys. Rev. 1965, 138, B554. Ho, J. M., Phillips, Ν. E., Phys. Rev. 1965, 140, A648. Keszthelyi, L., Cameron, J. Α., private communication. Stolovy, Α.,Bull.Am. Phys. Soc. 1965, 10, 17. Uher, R. Α., Sorensen, R. Α., Nucl. Phys. 1966, 86, 1. Wilenzick, R. M., Hardy, Κ. Α., Hicks, J. Α., Owens, W. R., Phys. Letters 1969, 29A, 670. RECEIVED December 16, 1969.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch010

(8) (9) (10) (11) (12) (13) (14) (15)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11

Double B o n d Isomerization as a ProductControlling Factor in Hydrogenation over

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

Platinum G r o u p Metals PAUL N. RYLANDER Engelhard Industries, Newark, N. J. 07105

A useful endeavor in catalysis is to describe properties of catalysts in terms that will correlate various phenomena and permit prediction. One such parameter is the relative tendency of catalysts to promote double bond migration during hydrogenation. This tendency relates to such dive events as catalyst poisoning, changes in the organic functio hydrogenolysis, loss of optical activity, and selectivity in hydrogenation of aliphatic and aromatic systems. 11 of the elements in the platinum group metals make hydrogénation catalysts, and among them they can catalyze the reduction of most organic functional groups. Both the rate and selectivity depend markedly on the metal. The number of organic compounds and the products derivable from them by hydrogénation is very large, and it is of considerable practical value to search for a few characteristics of catalysts that will permit some correlation of the catalytic metal with the type of product obtained. One of these useful characteristics is the relative ability of various catalysts to promote double bond isomerization in olefins prior to their saturation. The concept is applicable not only to olefins per se but also to compounds such as acetylenes and aromatics that are converted to olefins during hydrogénation. In the presentation that follows, a number of diverse phenomena will be correlated with this property. Double Bond Migration Olefins may undergo a facile double bond migration in the presence of hydrogen and a platinum metal catalyst. A relative order (palladium >> ruthenium > rhodium > platinum >> iridium) established (2) for 150 In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

Double

R Y L A N D E R

Bond

151

Isomerization

1-pentene, for the t e n d e n c y to p r o m o t e d o u b l e b o n d m i g r a t i o n d u r i n g hydrogénation, is p r o b a b l y g e n e r a l for most olefinic systems.

T h e extent

of i s o m e r i z a t i o n also d e p e n d s i m p o r t a n t l y o n t h e substrate.

For migra-

t i o n to occur, the a l l y l i c h y d r o g e n

to b e r e m o v e d

m u s t be

sterically

accessible to the catalyst a n d o n the same side of the m o l e c u l e as t h e entering hydrogen ( 5 ) .

T h e m e c h a n i s m i n v o l v e d m a y be c o m p l e x

M i g r a t i o n is d i m i n i s h e d b y the presence of h e a v y metals, amines, a n d e l e v a t e d pressure Selectivity

Among

Olefinic

(3).

hydroxides,

(15). Types

A u s e f u l g e n e r a l i t y i n p r e d i c t i n g selectivity is that the rate of h y d r o -

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

génation falls, b o t h a b s o l u t e l y a n d c o m p e t i t i v e l y , as steric a r o u n d the d o u b l e b o n d is i n c r e a s e d (23).

hinderance

O n this basis i n a m i x t u r e of

olefins, t e r m i n a l olefins w o u l d b e e x p e c t e d to be s a t u r a t e d p r e f e r e n t i a l l y to i n t e r n a l olefins, i f a p r i o r r a p i d e q u i l i b r a t i o n b y i s o m e r i z a t i o n d i d not ensue. T h i s thesis was d e m o n s t r a t e d the pairs of

olefins

shown

(1)

in Table

i n the selective hydrogénation of I, over r u t h e n i u m - o n - c a r b o n ,

a

catalyst w i t h r e l a t i v e l y l o w i s o m e r i z a t i o n a c t i v i t y . T h e experiments

were

c a r r i e d out b y p a r t i a l hydrogénation of a m i x t u r e of 1 m o l e of

each

olefin, a n d the r e a c t i o n was i n t e r r u p t e d a n d a n a l y z e d after of 1 m o l e of h y d r o g e n .

absorption

Those compounds underlined i n Table I were

r e d u c e d w i t h h i g h s e l e c t i v i t y i n preference

to the other m e m b e r of the

p a i r . T h i s h i g h degree of selectivity w a s l i m i t e d to those pairs of olefins

Table I.

Competitive Hydrogénation of Olefins by Ruthenium on Carbon 2-methyl-2-pentene

Selective

a n d 2 - m e t h y l - 1-pentene a n d 2-octene a n d cyclohexene and 2-methyl-1-pentene

Selective Selective

4-Methyl-1-pentene and 4-Methyl-l-pentene 4-Methyl-l-pentene 4-Methyl-l-pentene 2-Methyl-2-pentene

2 - M e t h y l - 2 - p e n t e n e a n d 2-octene 2 - M e t h y l - 2 - p e n t e n e a n d 1-octene 2 - M e t h y l - 2 - p e n t e n e a n d cyclohexene 2 - M e t h y l - l - p e n t e n e a n d 2-octene 2 - M e t h y l - l - p e n t e n e a n d 1-octene 2 - M e t h y l - l - p e n t e n e a n d cyclohexene 2-Octene a n d 1-octene 2-Octene a n d cyclohexene 1-Octene a n d cyclohexene

Selective N o t selective N o t selective Selective N o t selective N o t selective Selective N o t selective Selective N o t selective Selective

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

152

PLATINUM

GROUP

METALS

AND

COMPOUNDS

c o n t a i n i n g one t e r m i n a l a n d one i n t e r n a l olefin; other pairs w e r e r e d u c e d w i t h a m u c h l o w e r selectivity. T h i s same t y p e of d i s c r i m i n a t i o n b e t w e e n i n t e r n a l a n d t e r m i n a l olefins also has b e e n d e m o n s t r a t e d w h e n the t w o types of d o u b l e b o n d s w e r e i n the same m o l e c u l e . T h e s e hydrogénations w e r e c a r r i e d out w i t h w a t e r as a solvent, i f i n d e e d solvent is the correct w o r d to use w i t h olefins, b u t i f there w e r e no w a t e r present there w a s n o r e d u c t i o n . T h i s is a c o m m o n c h a r a c t e r i s t i c of r u t h e n i u m catalysis at l o w pressure. A t h i g h pressure, m a n y solvents c a n be u s e d , b u t e v e n here w a t e r sometimes has a s t r i k i n g l y b e n e f i c i a l effect o n the rate ( 3 2 ) . S e l e c t i v i t y of the t y p e f o u n d w i t h r u t h e n i u m w a s not possible w h e n p a l l a d i u m catalysts w e r e u s e d . F o r instance, hydrogénation of a m i x t u r e of 1- a n d 2-octene was c o m p l e t e l y nonselective over p a l l a d i u m catalysts. Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

T h i s l a c k of s e l e c t i v i t y r e s u l t e d f r o m the h i g h i s o m e r i z a t i o n a c t i v i t y of p a l l a d i u m ; w h e n the r e a c t i o n w a s s t o p p e d at o n l y one-tenth of

comple-

t i o n , a l l 1-octene h a d d i s a p p e a r e d b y m i g r a t i o n of the t e r m i n a l d o u b l e bond inward.

Migration to Inaccessible Positions T r i v i a l r e d u c t i o n s at times m a y b e r e n d e r e d difficult or i m p o s s i b l e b y i m p r o p e r selection of catalysts. T h i s is d e m o n s t r a t e d

(13)

b y the

hydrogénation of p u l c h e l l i n , I. O v e r p l a t i n u m oxide i n e t h a n o l , p u l c h e l l i n w a s r e d u c e d to d i h y d r o p u l c h e l l i n , I I . O n the other h a n d , r e d u c t i o n of p u l c h e l l i n over p a l l a d i u m - o n - c a r b o n or p a l l a d i u m - o n - c a l c i u m c a r b o n a t e afforded d i h y d r o p u l c h e l l i n i n 6 0 - 8 0 % y i e l d a c c o m p a n i e d b y the i s o m e r i z e d p r o d u c t , i s o p u l c h e l l i n , I I I . T h e s e results are i n k e e p i n g w i t h the greater t e n d e n c y of p a l l a d i u m to cause d o u b l e b o n d m i g r a t i o n . It w o u l d b e most difficult to convert i s o p u l c h e l l i n to d i h y d r o p u l c h e l l i n b y c a t a l y t i c hydrogénation, f o r a n y a t t e m p t to d o so p r o b a b l y w o u l d result i n h y d r o genolysis of the a l l y l i c c a r b o n - o x y g e n b o n d .

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

Double

R Y L A N D E R

Bond

153

Isomerization

T h e r e are m a n y other examples of d o u b l e b o n d m i g r a t i o n to a t e t r a s u b s t i t u t e d p o s i t i o n , a n d these i n c l u d e hydrogénations e v e n over p l a t i n u m , a catalyst w i t h a r e l a t i v e l y l o w i s o m e r i z a t i o n a c t i v i t y (24).

One

example, the a t t e m p t e d hydrogénation of the e x o c y c l i c d o u b l e b o n d of h y s t e r i n o v e r p l a t i n u m oxide, r e s u l t e d i n i s o m e r i z a t i o n to i s o h y s t e r i n , w h i c h w a s resistant to hydrogénation u n d e r the c o n d i t i o n s of the r e a c t i o n . H y s t e r i n (39)

w a s r e d u c e d successfully over r u t h e n i u m d i o x i d e at ele-

v a t e d temperatures a n d pressures. It is e x p e c t e d that the e l e v a t e d p r e s sures u s e d w i t h r u t h e n i u m w o u l d d i m i n i s h i s o m e r i z a t i o n , a n d t h e v i g o r o u s c o n d i t i o n s w i t h r u t h e n i u m also m i g h t be sufficient to r e d u c e i s o h y s t e r i n if i t f o r m e d .

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

Changes

in the Organic

Function

I s o m e r i z a t i o n d u r i n g hydrogénation m a y a l t e r the f u n c t i o n a l g r o u p s present i n the m o l e c u l e . 5%

F o r instance, r e d u c t i o n of c y c l o h e x e n - 2 - o l

over

p l a t i n u m - o n - c a r b o n o c c u r r e d w i t h r a p i d a b s o r p t i o n of 1 m o l e

of

h y d r o g e n at s u b s t a n t i a l l y constant rate a n d q u a n t i t a t i v e f o r m a t i o n of cyclohexanol.

O n t h e other h a n d , r e d u c t i o n over p a l l a d i u m ceased

ab-

r u p t l y at about t w o - t h i r d s of a m o l e , a n d the p r o d u c t w a s a m i x t u r e of c y c l o h e x a n o l a n d c y c l o h e x a n o n e , the latter a r i s i n g t h r o u g h d o u b l e b o n d m i g r a t i o n to the e n o l of c y c l o h e x a n o n e OH

Λ,

(29). OH

Ο

Λ

Λ,

5% P d / C

67%

33%

5% P t / C

100%

0%

T h i s t y p e of t r a n s f o r m a t i o n m a y o c c u r also b y a n exchange r e a c t i o n . C a t a l y t i c hydrogénation of

5-cyclodecen-l-ol

over

p l a t i n u m oxide

m e t h a n o l r e s u l t e d i n a b s o r p t i o n of 0.97 m o l a r e q u i v a l e n t s of

in

hydrogen

a n d f o r m a t i o n of the s a t u r a t e d a l c o h o l . H o w e v e r , w h e n 1 0 % p a l l a d i u m o n - c a r b o n i n a l c o h o l was u s e d as a catalyst, r e d u c t i o n w a s i n c o m p l e t e o w i n g to f o r m a t i o n of c y c l o d e c a n o n e .

T h e authors (8)

e x p l a i n e d the

e x c e p t i o n a l ease o f this t y p e of r e a c t i o n b y the s p a t i a l p r o x i m i t y of t h e a l c o h o l a n d olefin g r o u p s , f a v o r i n g a n i n t r a m o l e c u l a r h y d r o g e n transfer. P r e s u m a b l y , p a l l a d i u m is v e r y m u c h m o r e effective i n this transfer r e a c t i o n t h a n p l a t i n u m , b u t s i m i l a r transfer b y p l a t i n u m m i g h t pass u n o b s e r v e d , as this catalyst w o u l d r e d u c e the ketone so f o r m e d to a l c o h o l ; p a l l a d i u m is a r e l a t i v e l y p o o r catalyst for hydrogénation a l i p h a t i c ketones

(6).

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

the of

154

PLATINUM

GROUP

METALS

AND

COMPOUNDS

OH

OH

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

Catalyst

Inhibition

W i t h sufficient use, a l l catalysts u n d e r g o d e a c t i v a t i o n .

Two

broad

types of i n h i b i t i o n m a y be d i s t i n g u i s h e d . I n the first, the catalyst b e comes i n h i b i t e d t h r o u g h the i n t r o d u c t i o n of catalyst i n h i b i t o r s c a r r i e d i n t o the system b y the substrate, solvent, h y d r o g e n , o r e v e n f o r m e d

by

d i s s o l u t i o n of the reactor. I n the second t y p e , d e a c t i v a t i o n arises t h r o u g h some i n h i b i t o r f o r m e d i n the r e a c t i o n itself. A n e x a m p l e of the t y p e is p r o v i d e d b y the w o r k of N i s h i m u r a a n d H a m a (21).

second

These work-

ers f o u n d , c o n t r a r y to w h a t one m i g h t expect b y a n a l o g y to s i m i l a r s i t u a tions, that b e n z y l a l c o h o l w a s r e d u c e d m o r e s m o o t h l y to c y c l o h e x y l c a r b i n o l over

p l a t i n u m oxide

t h a n over

r h o d i u m catalysts.

The

rate

of

hydrogénation over r h o d i u m decreased m a r k e d l y d u r i n g the course

of

the r e a c t i o n , a c c o m p a n i e d

b y the f o r m a t i o n of i n c r e a s i n g amounts

of

cyclohexanecarboxaldehyde,

a strong i n h i b i t o r . R e d u c t i o n s over p l a t i n u m

catalyst, o n the other h a n d , p r o c e e d e d at a m o r e n e a r l y constant rate a n d w i t h the a c c u m u l a t i o n of less a l d e h y d e .

The inhibiting

b o x a l d e h y d e arose f r o m i s o m e r i z a t i o n of i n t e r m e d i a t e

cyclohexanecar-

1-cyclohexenylcar-

b i n o l . P l a t i n u m catalysts w e r e less i n h i b i t e d t h a n r h o d i u m b y t h e a l d e h y d e o n t w o counts.

T h e i n t e r m e d i a t e u n s a t u r a t e d c a r b i n o l w a s isomer-

i z e d less over p l a t i n u m t h a n r h o d i u m , a n d the a l d e h y d e once f o r m e d w a s h y d r o g e n a t e d a b o u t four to five times m o r e r a p i d l y over p l a t i n u m .

CH OH 2

CH OH 2

CHO

S i m i l a r isomerizations h a v e been o b s e r v e d i n the hydrogénation of p h e n y l e t h a n o l over r h o d i u m , w h e r e one of the i n t e r m e d i a t e p r o d u c t s is cyclohexylmethylketone.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

R Y L A N D E R

Double

Bond

155

Isomerization

T h i s ketone, u n l i k e c y c l o h e x a n e c a r b o x a l d e h y d e ,

is not a n i n h i b i t o r a n d

c a n b e o b t a i n e d as a n i n t e r m e d i a t e i n about 4 0 % y i e l d f r o m hydrogénat i o n of a c e t o p h e n o n e over r h o d i u m ; f u r t h e r r e d u c t i o n affords h i g h y i e l d s of c y c l o h e x y l m e t h y l c a r b i n o l

(28).

Hydrogenolysis of Carbon-Oxygen Bonds C a r b o n - o x y g e n b o n d s are not c l e a v e d r e a d i l y b y c a t a l y t i c h y d r o genolysis unless t h e y are i n some w a y a c t i v a t e d b y p r o x i m i t y to another function.

Benzylic, vinylic, and allylic oxygen bonds undergo a facile

h y d r o g e n o l y s i s , b u t f u n c t i o n s r e m o v e d f r o m the d o u b l e unless a p r i o r i s o m e r i z a t i o n occurs.

b o n d do

not

A n e x a m p l e of i s o m e r i z a t i o n l e a d i n g

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

to h y d r o g e n o l y s i s p r o d u c t s is f o u n d i n the hydrogénation of h e p t - 3 - y n e 1,7-diol over 5 % p a l l a d i u m - o n - b a r i u m sulfate; i n a d d i t i o n to t h e expected d i o l , a c o n s i d e r a b l e a m o u n t of 1-heptanol w a s f o r m e d ( 9 ) .

The forma-

t i o n of 1-heptanol is best a c c o u n t e d for b y the a s s u m p t i o n of r e d u c t i o n of the acetylene to the c o r r e s p o n d i n g olefin f o l l o w e d b y i s o m e r i z a t i o n of the d o u b l e b o n d i n t o a n a l l y l i c p o s i t i o n .

P l a t i n u m , or better r h o d i u m ,

w o u l d b e p r e f e r r e d to p a l l a d i u m i n examples of this t y p e .

Rhodium

w o u l d seem p a r t i c u l a r l y d e s i r a b l e o n t w o counts. T h e i s o m e r i z a t i o n a c t i v i t y of r h o d i u m is m u c h l o w e r t h a n that of p a l l a d i u m , a n d less a l l y l i c a l c o h o l w o u l d be f o r m e d i n the hydrogénation. A d d i t i o n a l l y , r h o d i u m has f o u n d c o n s i d e r a b l e use i n the r e d u c t i o n of a l l y l i c a n d v i n y l i c systems w h e n h y d r o g e n o l y s i s was to be a v o i d e d

(27).

H O C H C H C = C C H C H C H O H -> 2

2

2

2

2

HOCH CH CH = CHCH CH CH OH

->

HOCH CH = CHCH CH CH CH OH

-*

2

2

2

2

2

2

2

2

2

2

CH CH = CHCH CH CH CH OH 3

2

2

2

2

->

CH3CH CH CH CH CH CH OH 2

2

2

2

2

2

Hydrogenolysis of Carbon-Carbon Bonds A s t r i k i n g e x a m p l e of the effect i s o m e r i z a t i o n m a y h a v e is f o u n d i n the hydrogénation of car-3-ene ( 7 ) .

T w o different p r o d u c t s are o b t a i n e d

i n nearly quantitative yield, depending p l a t i n u m - o n - c a r b o n at 1500 p s i g , cis-carane

on

the

catalyst u s e d .

Over

was obtained i n 9 8 % y i e l d ,

whereas over p a l l a d i u m - o n - c a r b o n , q u a n t i t a t i v e y i e l d s of 1,1,4-trimethylcycloheptane could be achieved.

H y d r o g e n o l y s i s w i t h f o r m a t i o n of the

s e v e n - m e m b e r e d r i n g s w a s b e l i e v e d to be p r e c e e d e d b y i s o m e r i z a t i o n to car-2-ene.

If i s o m e r i z a t i o n is a p r e r e q u i s i t e for h y d r o g e n o l y s i s , i t is to b e

e x p e c t e d that less of the h y d r o g e n o l y s i s p r o d u c t w o u l d b e f o r m e d

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

over

156

PLATINUM

GROUP

METALS

AND

COMPOUNDS

p l a t i n u m , since p l a t i n u m is n o t as a c t i v e as p a l l a d i u m for d o u b l e b o n d

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

migration.

F o r m a t i o n of 1,1,4-trimethylcycloheptane f r o m car-3-ene d e p e n d s o n t w o properties of p a l l a d i u m , the strong t e n d e n c y of p a l l a d i u m to p r o m o t e i s o m e r i z a t i o n a n d to h y d r o g e n o l y z e v i n y l c y c l o p r o p a n e systems.

I n the

b i c y c l i c u n s a t u r a t e d a c i d , I V , p r i o r i s o m e r i z a t i o n is not necessary

to

m o v e the d o u b l e b o n d i n t o c o n j u g a t i o n , yet here, too, p l a t i n u m a n d p a l l a d i u m g i v e q u i t e different results. T h e s a t u r a t e d b i c y c l i c a c i d is f o r m e d over p l a t i n u m , w h e r e a s over p a l l a d i u m a m i x t u r e of c y c l o h e x a n e carboxylic acid and benzoic disproportionation

COOH

a c i d results t h r o u g h h y d r o g e n o l y s i s a n d

(20).

COOH

COOH

COOH

Disproportionation D i s p r o p o r t i o n a t i o n is a s p e c i a l f o r m of d o u b l e b o n d m i g r a t i o n i n w h i c h the d o u b l e b o n d is t r a n s f e r r e d f r o m one m o l e c u l e to another. R e a c t i o n s of this t y p e are e s p e c i a l l y l i a b l e to o c c u r over p a l l a d i u m , a n d for this reason p a l l a d i u m sometimes is best a v o i d e d i n olefin hydrogénat i o n w h e n the d o u b l e b o n d is c o n t a i n e d i n a n i n c i p i e n t a r o m a t i c system. D i s p r o p o r t i o n a t i o n a c t i v i t y i n the hydrogénation of c y c l o h e x e n e

(and

p r e s u m a b l y other i n c i p i e n t a r o m a t i c systems w i l l f o l l o w the same o r d e r ) decreases w i t h the m e t a l i n the o r d e r p a l l a d i u m > > p l a t i n u m > r h o d i u m (16).

A n e x a m p l e of the c o m p l i c a t i o n t h a t c a n be c a u s e d b y d i s p r o p o r -

t i o n a t i o n d u r i n g hydrogénation is f o u n d i n t h e a t t e m p t e d r e d u c t i o n of

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

Double

RYLANDER

Bond

157

Isomerization

the d i e n o n e , V , to the saturated ketone over p a l l a d i u m - o n - c a r b o n i n ether. T h e p r o d u c t m i x t u r e consisted of a b o u t 2 0 % i n d a n e , 2 0 % 1-indanone,

and 4 5 %

4,5,6,7-tetrahydro-l-indanone

o x y g e n f u n c t i o n w o u l d be

expected

(14).

once the c o m p o u n d

cis-hexahydroL o s s of has

a r o m a t i c , for p a l l a d i u m makes t h e best k n o w n catalyst for

the

become selective

hydrogénation of a n a r o m a t i c ketone to a n a r o m a t i c a l c o h o l a n d

for

h y d r o g e n o l y s i s of the a r o m a t i c a l c o h o l to t h e a r o m a t i c h y d r o c a r b o n .

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

0

Ο

Ο

Loss of Optical

Activity

U n s a t u r a t e d o p t i c a l l y active c o m p o u n d s h a v i n g a n a s y m m e t r i c center accessible

to a m i g r a t i n g d o u b l e

hydrogénation (4).

bond may undergo

a c t i v e olefin ( — ) - 3 , 7 - d i m e t h y l - l - o c t e n e oxide, a catalyst of racemization, but

low

over

product was 4 3 - 5 2 %

(15).

R e d u c t i o n over p l a t i n u m

isomerization activity, resulted i n only v a r y i n g amounts

racemized.

of

3%

palladium-on-carbon,

the

R a c e m i z a t i o n , a n d therefore b y i n f e r -

ence i s o m e r i z a t i o n , w e r e decreased a n d b y bases.

racemization on

A n e x a m p l e is the hydrogénation of the o p t i c a l l y

b y pressure, b y catalyst i n h i b i t o r s ,

R e d u c t i o n at 1500 p s i g over p a l l a d i u m - o n - c a r b o n gave

o n l y 2 3 % r a c e m i z e d p r o d u c t , over a L i n d l a r catalyst (19)

at 1 a t m gave

1 6 % , a n d over p a l l a d i u m - o n - c a r b o n i n the presence of s m a l l q u a n t i t i e s of p o t a s s i u m h y d r o x i d e or p y r i d i n e gave 12 a n d 1 8 % r a c e m i z a t i o n , respectively.

C e r t a i n l y , i n this c o m p o u n d , m i g r a t i o n of the d o u b l e b o n d

afford t h e 2-octene w i l l result i n r a c e m i z a t i o n i f the olefin is before

saturation, but

other

pathways

to

to

desorbed

r a c e m i z a t i o n also m a y

be

operative. Stereochemistry T h e extent of d o u b l e b o n d m i g r a t i o n d u r i n g r e d u c t i o n of a n olefin m a y influence m a r k e d l y the stereochemistry of the r e s u l t i n g p r o d u c t .

A

s t r i k i n g e x a m p l e is p r o v i d e d b y the w o r k of S i e g e l a n d S m i t h ( 3 5 )

on

hydrogénation of 1,2-dimethylcyclohexene.

O v e r p l a t i n u m oxide i n acetic

a c i d , this olefin afforded 8 2 % cis- 1,2-dimethylcyclohexane, whereas

over

palladium-on-alumina

The

the p r o d u c t

contained

73%

trans-isomer.

e x p l a n a t i o n for this u n e x p e c t e d l y large percentage of trans-isomer lies i n d o u b l e b o n d m i g r a t i o n to the 2 - p o s i t i o n or to the m e t h y l e n e p o s i t i o n . T h e stereochemistry of the p r o d u c t is i n a sense t h e r e s u l t a n t of c o m p e t i -

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

158

PLATINUM

GROUP

METALS

AND

COMPOUNDS

t i o n b e t w e e n rates of hydrogénation a n d rates of i s o m e r i z a t i o n of the i n d i v i d u a l olefinic species. I n general, it seems easier to r a t i o n a l i z e a s t e r e o c h e m i c a l r e s u l t t h a n it is to p r e d i c t i t . T h e stereochemistry of hydrogénation of olefins is s u c h that h y d r o g e n u s u a l l y is a d d e d as i f b y cis a d d i t i o n f r o m the catalyst to the side of the m o l e c u l e that is a d s o r b e d o n it (34),

but unfortunately it

is not a l w a y s easy to d e c i d e w h i c h side of t h e m o l e c u l e w i l l a d s o r b o n the catalyst. T h e consequence of d o u b l e b o n d m i g r a t i o n o n the stereochemistry of the p r o d u c t is f r e q u e n t l y , therefore, not easy to p r e d i c t .

Hydrogénation of Aromatic Rings

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

A r o m a t i c c o m p o u n d s are r e d u c e d over the six p l a t i n u m m e t a l g r o u p catalysts at w i d e l y different rates, as expected, b u t a d d i t i o n a l l y t h e p r o d ucts of r e d u c t i o n f r e q u e n t l y v a r y w i t h the m e t a l used.

M a n y of these

results m a y be c o r r e l a t e d i n terms of t w o parameters not o b v i o u s l y c o n n e c t e d to a r o m a t i c p r o p e r t i e s : the r e l a t i v e tendencies of these catalysts to p r o m o t e

d o u b l e b o n d m i g r a t i o n i n olefins a n d to p r o m o t e

hydro-

genolysis of v i n y l i c a n d a l l y l i c functions.

Hydrogenolysis of Vinylic and Allylic Functions A g e n e r a l i z a t i o n d e r i v e d f r o m m a n y studies is that the toward

hydrogenolysis

of

vinylic

and

allylic

h a l o g e n increases i n the o r d e r r u t h e n i u m ^ platinum

<;

irridium.

I n v i n y l i c systems

oxygen,

rhodium «

tendency

nitrogen,

and

p a l l a d i u m <ί

especially, p l a t i n u m favors

h y d r o g e n o l y s i s m o r e t h a n p a l l a d i u m ; i n a l l y l i c systems, the t r e n d is not so clear b u t appears to be the reverse (26).

I r i d i u m is p l a c e d i n this

sequence o n the basis of l i m i t e d d a t a .

Partial Hydrogénation of Aromatic Rings A l t h o u g h hydrogénation of c a r b o c y c l i c aromatics u s u a l l y leads to the f u l l y saturated d e r i v a t i v e , there is a b u n d a n t e v i d e n c e r e d u c t i o n s p r o c e e d t h r o u g h i n t e r m e d i a t e olefins.

that m a n y

Hydrogénation of c r e -

sols was a s s u m e d to p r o c e e d t h r o u g h f o r m a t i o n of a l l k i n d s of 1,2-dihydrocresols p r o d u c e d i n e q u a l amounts (38)

a n d hydrogénation of xylenes to

afford e q u a l q u a n t i t i e s of a l l t e t r a h y d r o x y l e n e s as i n t e r m e d i a t e s

(36).

O c c a s i o n a l l y w i t h catalysts h a v i n g h i g h a c t i v i t y for a r o m a t i c r i n g r e d u c t i o n a n d r e l a t i v e l y l o w a c t i v i t y for olefin s a t u r a t i o n , p a r t i a l r e d u c t i o n to olefins m a y be u s e f u l i n synthesis. F o r e x a m p l e , hydrogénation of benzene over r u t h e n i u m afforded cyclohexene cis-A -tetrahydroterephthalic 2

thalicacid

(12)

in 20%

yield and

acid was obtained i n 7 3 % y i e l d from tereph-

(31).

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11.

Double

RYLANDER

Bond

159

Isomerization

P r i o r to s a t u r a t i o n , i n t e r m e d i a t e olefins m a y u n d e r g o m i g r a t i o n , a n d i t is the extent of this step that accounts i n large p a r t for the v a r y i n g results over different catalysts. Hydrogénation

of

Anilines

Hydrogénation of a n i l i n e s u s u a l l y affords a s a t u r a t e d a m i n e as the m a j o r p r o d u c t , b u t several side reactions, i n c l u d i n g h y d r o g e n o l y s i s , r e ductive hydrolysis, and reductive coupling, m a y accompany d o m i n a t e the r e d u c t i o n . activated molecules

and even

H y d r o g e n o l y s i s is i m p o r t a n t o n l y i n c e r t a i n

(10).

Reductive Hydrolysis.

R e d u c t i v e h y d r o l y s i s of anilines to

cyclo-

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

hexanones, assumed to go t h r o u g h a n i m i n e - t y p e i n t e r m e d i a t e , c l e a r l y involves isomerization

(18). CH

,CH;

3

P a l l a d i u m , b y far the most effective of p l a t i n u m metals for i s o m e r i z a t i o n , is also the most effective i n this r e a c t i o n . T h e i s o m e r i z a t i o n i n v o l v e s not o n l y t a u t o m e r i z a t i o n of a n e n a m i n e to a n i m i n e , b u t a d d i t i o n a l l y , i s o m e r i z a t i o n of d o u b l e b o n d s

remote f r o m the a m i n e i n t o a v i n y l i c

p o s i t i o n . P l a t i n u m , r u t h e n i u m , a n d r h o d i u m afford m i x t u r e s of less c y c l o hexanols a n d m o r e d i m e t h y l c y c l o h e x y l a m i n e s

(17).

U n d e r v i g o r o u s c o n d i t i o n s ( 1 0 0 ° C a n d 1000 p s i g ) i n 2 5 %

aqueous

s u l f u r i c a c i d , the y i e l d of c y c l o h e x a n o l p l u s c y c l o h e x a n o n e f r o m d i m e t h y l a n i l i n e was 90, 75, a n d 1 3 % over 5 % p a l l a d i u m - , 5 % r h o d i u m - , a n d 5 % p l a t i n u m - o n - c a r b o n , r e s p e c t i v e l y (33).

T h e d e c r e a s i n g y i e l d p a r a l l e l s the

d e c r e a s i n g t e n d e n c y for m i g r a t i o n . R e d u c t i v e h y d r o l y s i s is f a v o r e d

by

s u b s t i t u t i o n o n the n i t r o g e n a t o m a t t r i b u t e d i n p a r t to the r e l a t i v e diffic u l t y of h y d r o g e n a t i n g h i n d e r e d enamines. Reductive Coupling. F o r m a t i o n of d i c y c l o h e x y l a m i n e (25)

in hy-

drogénation of a n i l i n e p r o b a b l y i n v o l v e s a d d i t i o n of c y c l o h e x y l a m i n e to a n i m i n e a n d subsequent h y d r o g e n o l y s i s of a c a r b o n - n i t r o g e n b o n d NH; :NH

+ NH;

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

(11).

160

PLATINUM

GROUP

METALS

AND

COMPOUNDS

T h e p e r cent of d i c y c l o h e x y l a m i n e f o r m e d i n hydrogénation of a n i l i n e increases w i t h catalyst i n t h e o r d e r r u t h e n i u m < r h o d i u m «

platinum,

a n o r d e r a n t i c i p a t e d f r o m the r e l a t i v e t e n d e n c y of these metals to p r o mote double b o n d migration a n d hydrogenolysis (30).

S m a l l a m o u n t s of

a l k a l i i n u n s u p p o r t e d r h o d i u m a n d r u t h e n i u m catalysts c o m p l e t e l y e l i m i nate c o u p l i n g reactions, p r e s u m a b l y t h r o u g h i n h i b i t i o n of h y d r o g e n o l y s i s a n d / o r i s o m e r i z a t i o n . A l k a l i w a s w i t h o u t effect o n r u t h e n i u m or r h o d i u m catalysts s u p p o r t e d o n c a r b o n , p o s s i b l y because the a l k a l i is a d s o r b e d o n carbon rather than metal

(22).

Phenols

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

O n hydrogénation, p h e n o l s m a y u n d e r g o

s a t u r a t i o n to the

h e x a n o l , h y d r o g e n o l y s i s of the c a r b o n - o x y g e n

cyclo-

b o n d , or partial h y d r o -

génation to the c y c l o h e x a n o n e .

Hydrogenolysis P a r t i a l r e d u c t i o n of p h e n o l s affords m i x t u r e s of a l l y l i c a n d v i n y l i c alcohols.

F r o m t h e g e n e r a l i t y d e r i v e d for a l i p h a t i c systems, t h e most

h y d r o g e n o l y s i s of this m i x t u r e is e x p e c t e d w i t h p l a t i n u m , p a l l a d i u m , a n d i r i d i u m catalysts, a n d m u c h less w i t h r h o d i u m a n d r u t h e n i u m , a n expectat i o n s u b s t a n t i a t e d i n p r a c t i c e . F o r e x a m p l e , hydrogénation of r e s o r c i n o l i n n e u t r a l m e d i u m affords 20, 19, a n d 7 0 %

cyclohexanediol over

ladium-, platinum-, and rhodium-on-carbon, respectively

pal-

Many

(29).

examples attest to the v a l u e of r h o d i u m a n d r u t h e n i u m at e l e v a t e d pressure i n a v o i d i n g h y d r o g e n o l y s i s .

Partial Reduction to Ketones K e t o n e s arise f r o m p h e n o l s b y i s o m e r i z a t i o n of u n s a t u r a t e d alcohols (37).

P a l l a d i u m is the most s u i t e d for this t y p e of r e a c t i o n because

of

its h i g h i s o m e r i z a t i o n a c t i v i t y c o u p l e d w i t h a v e r y l o w r a t e of r e d u c t i o n of the r e s u l t i n g ketones (6).

E x c e l l e n t y i e l d s of ketones often m a y b e

o b t a i n e d ; r h o d i u m w i l l g i v e at times q u i t e s u b s t a n t i a l y i e l d s of c y c l o h e x a nones ( 5 0 - 6 5 %

m e t h y l c y c l o h e x a n o n e s f r o m cresols)

( 3 8 ) , b u t i n other

r e d u c t i o n s s u c h as r e s o r c i n o l , little ketone a c c u m u l a t e s over either r h o d i u m or p l a t i n u m u n d e r c o n d i t i o n s w h e r e i t is a m a j o r p r o d u c t

over

palladium (29). W h e t h e r or not ketone a c c u m u l a t e s i n r e d u c t i o n of p h e n o l s

depends

a d d i t i o n a l l y o n the r e l a t i v e rates of hydrogénation of k e t o n e a n d p h e n o l i n c o m p e t i t i o n . F o r instance, e q u i m o l a r m i x t u r e s of r e s o r c i n o l a n d c y c l o hexanone i n e t h a n o l w e r e p a r t i a l l y h y d r o g e n a t e d over s e v e r a l catalysts;

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

11. RYLANDER

Double Bond Isomerization

161

over palladium-on-carbon, resorcinol was reduced to the exclusion of cyclohexanone, whereas over platinum-on-carbon the reverse was true. No such marked preference for substrate was observed in reduction over rhodium-on-alumina or rhodium-on-carbon (29). The problem of ordering platinum group metals for the relative rate of reduction of various functions in competition is, with few exceptions, unsolved. A generalized solution would do much to aid in the proper choice of metal for selective reduction of bifunctional compounds.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

Literature Cited (1) Berkowitz, L. M., Rylander, P. N., J. Org. Chem. 1959, 24, 708. (2) Bond, G. C., Rank, J. S., Proc. Intern. Congr. Catalysis, 3rd,W.M.H. Sachtleretal.,Eds., 1965, 2, 1225. (3) Bond, G.C.,Wells, P. B., Advan. Catalysis 1964, 15, 91. (4) Bonner, W. Α., Stehr, C. E., doAmaral, J. R., J. Am. Chem. Soc. 1958, 80, 4732. (5) Bream, J. B., Eaton, D.C.,Henbest, Η. B., J. Chem. Soc. 1957, 1974. (6) Breitner, E., Roginski, E., Rylander, P. N., J. Org. Chem. 1959, 24, 1855. (7) Cocker, W., Shannon, P. V. R., Staniland, P. Α., J. Chem. Soc. 1966, 41. (8) Cope, A. G., Cotter, R. J., Roller, G. G., J. Am. Chem. Soc. 1955, 77, 3594. (9) Crombie, L., Jacklin, A. G., J. Chem. Soc. 1957, 1622. (10) Freifelder, M., Stone, G. R.,J.Org. Chem. 1962, 27, 3568. (11) Greenfield, H., J. Org. Chem. 1964, 29, 3082. (12) Hartog, F., U. S. Patent 3,391,206 (July 2, 1968). (13) Hetz, W., Ueda, K., Inayama, S., Tetrahedron 1963, 19, 483. (14) House, H. O., Rasmusson, G. H., J. Org. Chem. 1963, 28, 27. (15) Huntsman, W. D., Madison, N. L., Schlesinger, S. I., J. Catalysis 1963, 2, 498. (16) Hussey, A. S., Schenach, Τ. Α., Baker, R. H., J. Org. Chem. 1968, 33, 3258. (17) Kuhn, R., Driesen, H. E., Haas, H. J., Ann. Chem. 1968, 718, 78. (18) Kuhn, R., Haas, H. J., Ann. Chem. 1958, 611, 57. (19) Lindlar, H., Helv. Chim. Acta 1952, 35, 446. (20) Meinwald, J., Labana, S. S., Chadha, M. S., J. Am. Chem. Soc. 1963, 85, 582. (21) Nishimura, S., Hama, M., Bull. Chem. Soc. Japan 1966, 39, 2467. (22) Nishimura, S., Shu, T., Hara, T., Takagi, Y., Bull. Chem. Soc. Japan 1966, 39, 329. (23) Rylander, P. N., "Catalytic Hydrogenation over Platinum Metals," p. 91, Academic Press, New York, 1967. (24) Ibid., p. 99. (25) Ibid., p. 355. (26) Ibid., p. 445. (27) Ibid., p. 447. (28) Rylander, P. N., Hasbrouck, L., Engelhard Ind. Tech. Bull. 1968, 8, 148. (29) Rylander, P. N., Himelstein, N., Engelhard Ind. Tech. Bull. 1964, 5, 43. (30) Rylander, P. N., Kilroy, M., Coven, V., Engelhard Ind. Tech. Bull. 1965, 6, 11. (31) Rylander, P. N., Rakonza, N. F., U. S. Patent 3,163,679 (December 22, 1964). (32) Rylander, P. N., Rakoncza, N., Steele, D. R., Bollinger, M., Engelhard Ind. Tech. Bull. 1963, 4, 95.

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

162

PLATINUM GROUP METALS AND COMPOUNDS

Rylander, P. N., Steele, D. R., Engelhard Ind., unpublished observations, 1963. Siegel, S., Advan. Catalysis 1966, 16, 123. Siegel, S., Smith, G. V.,J.Am. Chem. Soc. 1960, 82, 6082, 6087. Siegel, S., Smith, G. V., Dmuchovsky,B.,Dubbel, D., Halpren, W., J. Am. Chem. Soc. 1962, 84, 3136. Smith, Η. Α., Stump, B. L.,J.Am. Chem. Soc. 1961, 83, 2739. Takagi, Y., Nishimura, S., Taya, K., Hirota, K.,J.Catalysis 1967, 8, 100. Vivar, A. R. de, Bratoeff, Ε. Α., Rios, T.,J.Org. Chem. 1966, 31, 673. RECEIVED December 16, 1969.

Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch011

(33) (34) (35) (36) (37) (38) (39)

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

INDEX A

Absorption spectra. .83-4, 86, 88, 91,140 Accuracy in bond lengths 121 Acetonitrile Ill Activation parameters 117 Adducts CO 124 CS 123 molecular 121 N 123 nitrosyl 124 S0 123 tetracyanoethylene 124 Alloys, ordered 7 Allylic functions, hydrogenolysis of 158 Ambidentate ligand Ill Anilines, hydrogénation of 159 Anisotropy, magnetic 11 Antiferromagnetism 1 Aqueous solutions 110 Aromatic rings, hydrogénation of . . 158 Aryl, silyl, and germyl derivatives 104 2

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2

2

Β Binuclear nitrides Bonding problems Bond lengths

56 99 124

Canted-ferrimagnetic structure . . . 9 CaPd 0 34 Catalyst hydrogénation 150 inhibition 154 Cationic complexes 57 CdPd 0 34 Chalcogenides, platinum metal . . . 17 Chemical shift 99 (CH ) PtC10 110 C O adducts 124 Coercive force 10 Competitive hydrogénation 151 Conduction bands 18 Conversion coefficient 140 Coupling constant 103 Crystal chemistry and synthesis 28 spectra 95 structure 7,18,44,120 Crystallite distribution 11 Crystallographic relationships 10 3

4

3

4

3

4

8 13

D Debye temperature 145-6 Debye-Waller factor 138 Delocalized 7r-systems involving Pt metals, structures of 129 Dimethylsulfoxide Ill Disordered structure 41 Disproportionation 156 Distortion 132 2,5-Dithiahexane complexes of RhCl 109 Double bond isomerization 150 migration 150 Dynamics, lattice 138 Dynamic systems 112 3

£ Electrical conductors resistivity Electron capture decay Electronic spectra

17 6 136 61,76

F

C 3

Curie point behavior ferromagnetic

Fermi contact term Ferromagnetic alloys Curie points Ferromagnetism Fluorophenyl derivatives Frozen-in flux

103 141 13 1 104 15

G Geometrical isomers

109,112

H Heteronuclear double resonance spectra 105 Hexahalo-complexes, spectra of . . 75 Hydride resonance 117 Hydrido complexes 66,106 organo and 112 preparative methods for 67 properties of 68 reaction of 70

163

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

164

PLATINUM

Hydrogénation anilines aromatic rings catalysts competitive Hydrogenolysis of vinylic and allylic functions . . Hyperfine interaction Hysteresis loops

159 158 150 151 155 158 143 14

METALS

AND

COMPOUNDS

Ν Neutrons, scattering of Nitrosyl adducts N adducts Nuclear properties N M R spectra Nitride ion Nitrido complexes 2

138 124 123 99 98 54 54

Ο

I

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GROUP

Infrared spectra 42,47,50 Inhibition, catalyst 154 Interaction, hyperfine 143 Interatomic distances 36, 128 Internal magnetic field 145 Iridium 5,19, 54, 70, 80, 95,122 Iron moment 4 Isomeric shift 144,147 Isomerization, double bond 150

Κ

Olefins 150 Optical activity, loss of 157 Ordered alloys 7 Ordering alloy 10 Organic function, changes in . . . . 153 Organo and hydrido derivatives . . 112 Osmium 14,54,80,95,98

Ρ Palladium . . 1, 21, 28,129, 152,156,159 oxides 28 Paramagnetism 99 Pb0 46 PbPd0 29 Phenols 160 Platinum 3, 9, 21,39, 76, 81, 86, 98,125,135,154 alkyls 103 dioxide, reaction of 39 metal chalcogenides 17 (II) phosphine complexes 102 Predicted proton resonance spectrum 107 Preparative methods for hydrido complexes 67 Properties of hydrido complexes . . 68 i95Pt chemical shifts 99 iS-Pt0 43 Pyrite structure 18 Pyrochlore series 47 structures 48 2

Ketones, partial reduction to . . . .

160

L Lattice dynamics Li^and substitution Local moments

138 112 4

M

Magnetic anisotropy circular dichroism moment ordering permanent properties susceptibility Magnetization saturation Marcasite structure Mass susceptibility Metallic properties Metal-olefin bond Mg Pd0 Migration double bond Molecular adducts Moment iron local magnetic M O - P t 0 system M02-Pt0 system M 0 - P t 0 system Mossbauer fractions spectra spectroscopy 2

4

2

2

2

11 84 4,144 17 1 1 1 6,8 10 20 2 18 113 37 152 150 121

3

2

·

4 4 4 49 43 47 146 142-3 135

2

2

R Racemization 157 Reactions of hydrido complexes . . 70 Recoilless resonance experiments . . 135 Remanence 15 Resonance effect 137 Rhodium 4, 7,19, 24,122,154 Rotation 113 Ruthenium . . . . 14, 17, 54,123,151,158 Rutile structure 46

S Sandwich-like structure Saturation magnetization Scattering of neutrons and x-rays . . Selectivity Signs of the spin-spin coupling constants

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

21 10 138 151 105

165

INDEX

S 0 and C S adducts 123 Solvation and solvent effects 109 number 110 Spectra absorption 83—4,86,88,91 crystal 95 electronic 61 electronic absorption 76 infrared 42,47,50 in organic media 89 Mossbauer 142-3 of hexahalo-complexes 75 of P t C l 81 predicted proton resonance . . . . 107 vibrational 59,60,64 Spectroscopic qualities, ultraviolet 74 Spectroscopy, Mossbauer 135 Spinel 49 Spin-spin coupling 102,115 Square planar complexes 108 hydrides 101 SrPd 0 34 Sr Pd0 31 Stereochemistry 105,124,157 Structure marcasite 20 pyrite 18 sandwich-like 21 tetragonal 23 Susceptibility magnetic 1 mass 2 2

2

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4

3

2

2

Symmetry patterns Synthesis and crystal chemistry . .

87 46 28

Τ Terminal nitrido complexes . . 55 Tetracyanoethylene adducts 124 Tetragonal structure 23 Thermal expansion 139 Trans influence 103,115,124 Trimethylplatinum (IV) complexes 106 oxinate 108 Trinuclear complex iridium 63 osmium 62

U Ultraviolet spectroscopic qualities 74 Vibrational spectra 59,80,64 Vinylic functions, hydrogenolysis of 158

4

W

3

Water exchange

112

X-ray diffraction powder data 30, 32, 35, 41, 52 X-rays, scattering of 138 X-ray structure determinations . . . 120

In Platinum Group Metals and Compounds; Rao, U.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.