Platinum Group Metals and Compounds - ACS Publications

9

Crystal Structures of Complexes of the

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Platinum G r o u p Metals 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 Rao; Platinum Group Metals and Compounds 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 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

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


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.


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 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.


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

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


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. 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


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 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 ) .



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


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

(—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 120° with errors of 1° or less.


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 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 15, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch009

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°

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


130


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


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 .

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


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.


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.



9. AMMA

Crystal Structure of Complexes

133

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