Extended Interactions between Metal Ions - ACS Publications

21 Directed Synthesis o f Linear Chain Metal Complexes with Well-Defined Cooperative Properties R. ADERJAN, D. BAUMANN, H. BREER, H. ENDRES, W. GITZEL, H. J. KELLER,

Downloaded by UNIV OF ARIZONA on November 26, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/bk-1974-0005.ch021

R.

LORENTZ,

W.

MORONI,

M.

MEGNAMISI-BÉLOMBÉ,

D.

NÖTHE,

and

H. H. RUPP A n o r g a n i s c h - C h e m i s c h e s Institut der Universität H e i d e l b e r g , D 6900 H e i d e l b e r g 1, I m N e u e n h e i m e r Feld 7, GFR

Abstract A s i m p l e band model deduced from t h e one-electron metal functions split by an electric field of the ligands c a n be successfully u s e d as a guideline in the directed synthesis of linear chain transition metal complexes with strong intermolecular interactions. One-dimensional metallic behaviour c a n be f o u n d for instance in planar transition m e t a l compounds w i t h 8 d-electrons b u t o n l y if small a n d strongly π-electron accepting equatorial ligands are used. Suitable ligands are carbonyl and isonitrile groups in connec tion with iridium(I) and r h o d i u m ( I ) ions. I.r., H-n.m.r., 195Pt-n.m.r., e.s.r., u.v. and 193Ir-Mößbauer spectra show that increasing increasing and increasing electron donating properties of the ligands considerably decrease the strength of the intermolecular metal interactions. A planar transition m e t a l complex w i t h less t h a n 8 d-electrons p e r m e t a l s h o u l d be far better suited for the formation of 1d-metals. But b e c a u s e o f t h e strong L e w i s acid activity of these compounds t h e donating solvent m o l e c u l e s occupy the axial positions of the central m e t a l atom and h e n c e prevent the self-association necessary for the building up o f a linear chain. Preparative procedures to o v e r c o m e t h e s e p r o b l e m s a r e p r o p o s e d . The structure and c h e m i c a l properties o f one o f t h e obtained "mixed valence" solids which contains a linear I-3-chain additionally is especially interesting since two n o n d e generate conduction spines are running closely parallel t o e a c h o t h e r t h r o u g h t h e lattice. 1

I.

Introduction Very

recently

i t was

shown b y

a.c.

and

d.c.

314

In Extended Interactions between Metal Ions; Interrante, L.; ACS Symposium Series; American Chemical Society: Washington, DC, 1974.

con-

21.

ADERJAN ET AL.

Linear

Chain

d u c t i v i t y m e a s u r e m e n t s a s w e l l a s by o p t i c a l , X - r a y a n d n e u t r o n s c a t t e r i n g e x p e r i m e n t s t h a t a t l e a s t one o f t h e many l i n e a r c h a i n m e t a l c o m p l e x e s - a p l a t i n u m c o m p l e x o f s t o i c h i o m e t r y K [ P t ( C N ) 2 | ] B r 3 · 3H2O - b e haves l i k e a o n e - d i m e n s i o n a l m e t a l a t room t e m p e r a t u r e (1). While the e v i d e n c e f o r a l d - m e t a l l i c s t a t e i n t h i s "mixed v a l e n c e " p l a t i n u m s y s t e m a t room temperat u r e i s o v e r w h e l m i n g and w i d e l y a c c e p t e d , t h e i n t e r p r e t a t i o n o f the phase t r a n s i t i o n s which o c c u r a t l o wer t e m p e r a t u r e s a n d w h i c h d e s t r o y t h e l d - m e t a l l i c s t a t e seems t o be c o n t r o v e r s i a l . T h i s c o n t r o v e r s y mot i v a t e s the search f o r other l d - m e t a l l i c t r a n s i t i o n metal complexes. In order to study the aptitude of l i n e a r metal c h a i n compounds t o f o r m l d - m e t a l s , f i r s t p r i n c i p l e s must be d e v e l o p e d t o d i r e c t a s y n t h e s i s o f t h e b e s t s u i t e d m o l e c u l e s f o r b u i l d i n g up l i n e a r l d - m e t a l l i c c h a i n s . T h i s problem w i t h r e s p e c t to the h i g h l y cond u c t i n g o r g a n i c c h a r g e t r a n s f e r s a l t s o f t h e "TCNQ" t y p e was r e c e n t l y d i s c u s s e d b y H e e g e r a n d G a r i t o ( 2 ) a n d w i l l be o u t l i n e d i n t h e f o l l o w i n g s e c t i o n s u s i n g p l a n a r m e t a l complexes as l a t t i c e e l e m e n t s . These planned syntheses give r i s e to the f o l l o w i n g questions: "Which k i n d o f m o l e c u l a r p a r a m e t e r s o f t h e i n d i v i d u a l e l e m e n t s g o v e r n t h e p r o p e r t i e s o f t h e s e s o l i d s ? " and "What s p e c i a l r u l e s c a n be s e t up t o p r e p a r e s u i t a b l e compounds i n a s y s t e m a t i c w a y ? " I n o r d e r t o f i n d s u c h r u l e s f o r the s y n t h e s i s of t a i l o r - c u t molecules, the e l e c t r o n i c s t r u c t u r e o f p l a n a r t r a n s i t i o n m e t a l comp l e x e s , which c r y s t a l l i z e p r e f e r a b l y i n columnar s t a c k s w i t h d i r e c t m e t a l c o n t a c t s , h a s t o be i n v e s t i gated . 2


315

Complexes

II.

Electronic

structure

of suitable

0 #

metal

complexes

T h e i n t e r m o l e c u l a r c o n t a c t s i n t h e known l i n e a r c h a i n m e t a l compounds w i t h d i r e c t m e t a l - m e t a l b o n d s a r e b r o u g h t a b o u t m a i n l y by t h e c e n t r a l m e t a l s d-elect r o n s . Though most o f t h e c o m p l e x e s have c o v a l e n t l y bonded l i g a n d s an o v e r l a p o f d - f u n c t i o n s o f t h e c e n t r a l metal ions with a p p r o p r i a t e l i g a n d f u n c t i o n s can be o m i t t e d i n a f i r s t a p p r o x i m a t i o n , t o k e e p t h e m o d e l as c l e a r as p o s s i b l e . A v e r y s i m p l e and p e r h a p s o v e r s i m p l i f i e d p u r e c r y s t a l f i e l d a p p r o a c h c a n be u s e d t o e x p l a i n t h e e l e c t r o n i c s t r u c t u r e o f t h e s o l i d s . The c e n t r a l m e t a l i o n s o f p l a n a r t r a n s i t i o n m e t a l comp l e x e s r e s i d i n g i n columnar s t a c k s a r e exposed t o a tetragonally distorted octahedral ligand f i e l d (fig.l) e x e r t e d by t h e f o u r e q u a t o r i a l l i g a n d s a n d t h e two a d j a c e n t m e t a l i o n s i n t h e a x i a l p o s i t i o n s . The d e g r e e



EXTENDED

INTERACTIONS

BETWEEN

METAL

Figure 1. Energies of d-electrons in a onedimensional linear chain d -configurated transition metal complex 8


IONS

21.

Linear

ADERJAN ET AL.

Chain

317

Complexes

o f t e t r a g o n a l d i s t o r t i o n depends on t h e r e l a t i v e " s t r e n g t h " o f t h e a x i a l and e q u a t o r i a l l i g a n d g r o u p s . E q u a l s t r e n g t h o f a x i a l and e q u a t o r i a l l i g a n d s r e s u l t s i n an " o c t a h e d r a l " f i e l d w i t h d e g e n e r a t e d 2 - a n d d 2_ 2 - l e v e l s . I f intermolecular i n t e r a c t i o n s are i n c l u d e d bands a r e o b t a i n e d the w i d t h o f which depends u p o n t h e d e g r e e o f o v e r l a p b e t w e e n t h e one e l e c t r o n d f u n c t i o n s . The b e s t i n t e r m o l e c u l a r o v e r l a p i s a s s u m e d between the d 2 - f u n c t i o n s , w h i l e the o r b i t a l s locali zed m a i n l y i n the complex p l a n e are l e s s s u i t e d f o r i n t e r a c t i o n s and t h e r e f o r e g i v e v e r y s m a l l b a n d s . P a r t i c i p a t i o n o f l i g a n d o r b i t a l s c o u l d be a d d e d e a s i l y i f n e c e s s a r y but would not g i v e a q u a l i t a t i v e l y d i f f e r e n t p i c t u r e . T h i s model c o u l d i n c o n t r a s t t o e a r l i e r pro p o s e d e n e r g y l e v e l d i a g r a m s (3> *0 g i v e a more a d e quate d e s c r i p t i o n of the e l e c t r o n i c s t r u c t u r e of these s o l i d s , b e c a u s e an a p p r e c i a b l e m i x i n g o f m e t a l s- and p - s t a t e s seems f a i r l y u n l i k e l y w i t h r e s p e c t t o t h e l a r g e e n e r g y d i f f e r e n c e s o f a b o u t 15 eV i n v o l v e d ( 5 ) . What k i n d o f c o n s e q u e n c e s c a n be d r a w n f r o m t h i s scheme? T h i s q u e s t i o n i s f i r s t a n s w e r e d i n c o n t e x t w i t h d ° - c o m p l e x e s . M o s t o f t h e known l i n e a r m e t a l c h a i n compounds w i t h d i r e c t m e t a l - m e t a l c o n t a c t s c o n t a i n metal ions with 8 d-electrons (4). In t h i s case, a l l the bands a r e f i l l e d w i t h e l e c t r o n s w i t h the ex c e p t i o n o f the d 2 „ 2 - b a n d . T h i s model p r e d i c t s i f the t e t r a g o n a l d i s t o r t i o n i s a p p r e c i a b l e and t h e e n e r g y gap Λ Ε i s q u i t e l a r g e , a s e m i c o n d u c t i n g b e h a v i o u r a n d o n l y weak i n t e r m o l e c u l a r i n t e r a c t i o n s . On t h e o t h e r hand the model c o u l d e x p l a i n l d - m e t a l l i c b e h a v i o u r o f d ° - c o m p o u n d s as w e l l . S t r o n g l y e l e c t r o n a c c e p t i n g l i gands w i l l d e c r e a s e the energy s e p a r a t i o n between the d 2a n d d 2 - y 2 - o r b i t a l s a n d t h e e n e r g y gap w o u l d v a n i s h i n a f o r m a l l y " o c t a h e d r a l " f i e l d . The former c a s e i s t h a t what i s a c t u a l l y f o u n d i n m o s t known l i n e a r c h a i n d ° - m e t a l compounds. But t h i s model c l e a r l y h i n t s a t t h e s t r e n g t h e n i n g o f t h e p r e d i c t e d weak i n t e r a c t i o n s i n d°-complexes with l a r g e Δ Ε . T h i s g o a l c o u l d be a c h i e v e d i f i t i s p o s s i b l e t o : i) d i m i n i s h t h e e n e r g y gap b e t w e e n t h e d 2 and d 2 - y 2 - b a n d s by u s i n g s u i t a b l e e l e c t r o n a c c e p t i n g ligands, ii) o x i d i z e t r a n s i t i o n metal complexes c r y s t a l l i z i n g i n c o l u m n a r s t a c k s , so t h e f i l l e d d 2 - b a n d w i l l be d e p o p u l a t e d a n d a p a r t i a l l y o c c u p i e d b a n d r e s u l t s no m a t t e r how large ΔΕ i s , i i i ) s y n t h e s i z e l i n e a r c h a i n m e t a l complexes w i t h l e s s than 8 d-electrons per metal s i t e . x

y


z

x

z

y

x

z

x

z


318

EXTENDED

INTERACTIONS

BETWEEN

METAL

IONS


III. tion

C h o i c e o f S p e c t r o s c o p i c Methods f o r I d e n t i f i c a of Co-operative Phenomena A f t e r h a v i n g s e t up r u l e s f o r s e l e c t i n g s u i t a b l e compounds t h e r e r e m a i n s t h e q u e s t i o n o f how t o i d e n t i fy the v a r i a t i o n of i n t e r m o l e c u l a r i n t e r a c t i o n s i n diff e r e n t c o m p l e x e s on a q u a n t i t a t i v e b a s i s . I t i s n e c e s s a r y t o f i n d s p e c t r o s c o p i c methods w h i c h a r e a b l e t o i d e n t i f y i n t e r m o l e c u l a r i n t e r a c t i o n s and t o c l a s s i f y t h e i r s t r e n g t h . The m e t h o d s s h o u l d w o r k o n p o l y c r y s t a l l i n e samples s i n c e the p r e p a r a t i o n o f l a r g e s i n g l e c r y s t a l s i s often very difficult. In g e n e r a l , the u s u a l l y s u c c e s s f u l s p e c t r o s c o p i c m e t h o d s : o p t i c a l , e . s . r . , n.m.r., e . g . c a n be u s e d t o i d e n t i f y c o l l e c t i v e e l e c t r o n b e h a v i o u r . E s p e c i a l l y obvious are the r e s u l t s of X-ray s t r u c t u r e determination (M-M d i s t a n c e s ) and o f o p t i c a l methods i n t h e v i s i b l e a n d n e a r i n f r a r e d r e g i o n . The i n t e r m o l e c u l a r i n t e r a c t i o n s c a u s e an i n t e n s e e l e c t r o n i c t r a n s i t i o n , w h i c h i n s i n g l e c r y s t a l s i s l i n e a r l y p o l a r i z e d p a r a l l e l to the d i r e c t i o n o f t h e m e t a l c h a i n s and o f t e n a p p e a r s as a s t r i k i n g a n i s o t r o p i c m e t a l l i c l u s t r e i n c a s e s where strong i n t e r a c t i o n s take place (1). T h e r e a r e two m e t h o d s n a m e l y n.m.r. a n d Moftbauer s p e c t r o s c o p y , w h i c h c a n and h a v e b e e n u s e d t o m e a s u r e e l e c t r o n d e n s i t y at the p o s i t i o n o f metal n u c l e i i n the c h a i n a n d s o s h o u l d be a b l e t o i d e n t i f y co-operat i v e e l e c t r o n i c i n t e r a c t i o n s . Results of these two methods a r e l a t e r d i s c u s s e d i n c o n n e c t i o n w i t h t h e irid i u m a n d p l a t i n u m c o m p o u n d s . O t h e r m e t h o d s ; e . s . r . ar^d n e u t r o n s c a t t e r i n g e x p e r i m e n t s h a v e b e e n u s e d by d i f f e r e n t groups t o examine the c o l l e c t i v e s t a t e i n l i n e a r c h a i n compounds. IV.

Choice

of

suitable transition

metal

compounds

What we h a d t o do f i r s t o f a l l was t o s y n t h e s i z e l i n e a r c h a i n m e t a l compounds w i t h m o d e r a t e i n t e r m o l e c u l a r i n t e r a c t i o n s , to vary t h e i r molecular c o n s t i t u t i o n s y s t e m a t i c a l l y and t o i n v e s t i g a t e t h e i r c h a n g i n g s o l i d s t a t e p r o p e r t i e s by s p e c t r o s c o p i c m e t h o d s . I t i s r e a s o n a b l e t o s t a r t w i t h known l i n e a r c h a i n t r a n s i t i o n m e t a l c o m p l e x e s , t h e s t r u c t u r e s o f w h i c h a r e p r o v e d by X - r a y a n a l y s i s . On t h e s e s e l e c t e d s p e c i e s a s y s t e m a t i c v a r i a t i o n o f l i g a n d p r o p e r t i e s by p r e p a r a t i v e chemical m e t h o d s c o u l d be a c h i e v e d w i t h o u t m a j o r s t r u c t u r a l c h a n g e s . The p r o p e r t i e s o f d ° - c o m p o u n d s w e r e i n v e s t i g a t e d f i r s t l y . The f o l l o w i n g t y p e s o f c o m p l e x e s w i t h l i n e a r m e t a l c h a i n s a n d 8 d - e l e c t r o n s p e r c e n t r a l met a l i o n a r e known:


21.

Linear

ADERJAN ET AL.

Chain

319

Complexes

1

T e t r a h a l o g e n o m e t a l a n i o n s o f t h e t y p e [M X i | ] n w i t h X = C l " , B r ~ , CN" l i k e [ P t ( C N ) i | ] 2 - ( 3 ) . 2 Complex-cations o f the typé[M L ^ ] w i t h L a monod e n t a t e n e u t r a l d o n o r l i k e NH3 or i s o n i t r i l e . The c a t i o n [Rh(CNR)i|] i s a s i m p l e example f o r t h i s g r o u p o f compounds ( 6 , 7 ) . 3 In m i x i n g both types o f complexes s t a c k s w i t h a l t e r n a t i n g c a t i o n s and a n i o n s a r e o b t a i n e d (Magnus G r e e n S a l t e.g.) (4, 8). 4 Planar d i c a r b o n y l m e t a l ( I ) s p e c i e s c o n t a i n i n g the m e t a l s r h o d i u m a n d i r i d i u m . To t h i s g r o u p b e l o n g t h e numerous d e r i v a t i v e s o f (Pentan-2,4-dionato) d i c a r b o n y l i r i d i u m ( I ) and r h o d i u m ( I ) (9, 10, 11) . A s i m p l e compound o f t h i s t y p e i s I r ( C 0 ) ^ C l ( 1 2 ) . 5 B i s (oc,ft-diondioximato)metal(II) complexes (47T 6 B i s ( m a l e o d i n i t r i l e d i t h i o l a t o ) m e t a l ( I I ) compounds (13). O t h e r known s p e c i a l e x a m p l e s o f compounds w i t h c o l u m n a r s t r u c t u r e and d ^ - c e n t r a l m e t a l - i o n s a r e c l a s s i f i e d i n t o one o f t h e a b o v e g r o u p s . T h e r e a r e o n l y a few compounds known e a r l i e r w h i c h c o u l d be c l a s s i f i e d a s " m i x e d v a l e n c e " compounds w i t h d i r e c t m e t a l - m e t a l i n t e r a c t i o n s and a r e as f o l lows : The m o s t f a m o u s e x a m p l e s a r e t h e " m i x e d v a l e n c e " s o l i d s d e r i v e d from the p l a t i n u m ( I I ) complex i o n s n

+

+


1

[Pt(CN)2|]2- and

[Pt^OlOç] " 2

(3) .

H a l o g e n o c a r b o n y l i r i d i u m a n d p o s s i b l y r h o d i u m comp o u n d s s y n t h e s i z e d f i r s t l y by M a l a t e s t a ( 1 4 ) . P a r t i a l l y o x i d i z e d Bis (c*,&-diondioximato)metal(II) compounds c o n t a i n i n g a d d i t i o n a l l i n e a r i o d i n e c h a i n s (15).

V.

Systematic

Variation

of Ligand

Parameters

There are s e v e r a l well-known examples o f the var i a t i o n of metal-metal i n t e r a c t i o n s with the kind of l i g a n d . The compounds K 2 P t C l i | a n d i t s d e r i v a t i v e s may be u s e d a s a s i m p l e e x a m p l e o f t h e c h a n g e s w h i c h c a n be d o n e o n t h i s t y p e o f c o m p l e x e s a n d what s o l i d s t a t e c o n s e q u e n c e s w i l l be e x p e c t e d . The i n t e r m o l e c u l a r i n t e r a c t i o n s b e t w e e n t h e p l a t i n u m atoms a r e a l m o s t zero i n s o l i d I ^ P t C l i j . A l a r g e e n e r g y gap Δ Ε c a u s e s solid s t a t e p r o p e r t i e s t o show no s i g n o f c o l l e c t i v e e l e c t r o n behaviour. T h e r e f o r e , the i n t e r m o l e c u l a r platinump l a t i n u m d i s t a n c e i s q u i t e l a r g e ( 4 , 13 A) ( 1 6 ) . How e v e r , as p o i n t e d out i n t h e d e s c r i b e d c r y s t a l f i e l d m o d e l , t h e i n t e r m e t a l l i c i n t e r a c t i o n s c a n be e n h a n c e d h e a v i l y by u s i n g more e l e c t r o n w i t h d r a w i n g l i g a n d s than c h l o r i n e ; e s p e c i a l l y π-acceptors ( e . g. cyano-groups).


320

EXTENDED

INTERACTIONS

BETWEEN

METAL

I n a s i m p l e e n e r g y scheme t h i s r e s u l t s i n a lowering of the energy of the d 2-y2-band d i m i n i s h i n g the energy g a p . A c t u a l l y t h e P t - P t - d i s t a n c e s i n [Pt(CN)i|] compounds a r e c o n s i d e r a b l y d e c r e a s e d a n d some o f t h e s o l i d s t a t e p r o p e r t i e s o f compounds o f t h i s t y p e c l e a r l y show t h e e f f e c t o f a n i s o t r o p i c intermolecular i n t e r a c t i o n s ( 3 ) . Comparison of d i f f e r e n t s o l i d M [ P t ( C N ) i | ] o r M* [ P t ( CN ) 4 ] s p e c i e s p o i n t s o u t t h a t a t l e a s t one more i m p o r t a n t p a r a m e t e r b e s i d e s t h e " e l e c t r o n i c " f a c t o r h a s t o be c o n s i d e r e d , t h e s t e r i c r e q u i r e m e n t s o f t h e l a t t i c e e l e m e n t s . T h i s i s p r o v e d by the d é p e n d a n c e o f i n t e r m o l e c u l a r m e t a l i n t e r a c t i o n s on h y d r a t i o n sphere around the c a t i o n s (3)» F u r t h e r m o r e t h e i n t e r a c t i o n c a n be e n h a n c e d by a d d i n g e l e c t r o s t a t i c a t t r a c t i o n between l a t t i c e e l e ments i n s t e a d o f r e p u l s i o n i n t h e p u r e l y a n i o n i c s t a c k s of P t C l j i . Magnus Green S a l t with a l t e r n a t i n g [Pt(NH3) ] a n d P t C l / j " u n i t s and P t - P t d i s t a n c e s of 3.25 A shows c o n s i d e r a b l y e n h a n c e d i n t e r m o l e c u l a r i n t e r a c t i o n s w i t h a n e n e r g y gap ΔΕ o f a b o u t 0.7 eV (17). B u t t h e s e compounds a r e n o t w e l l s u i t e d f o r o u r s p e c i a l purpose. In o r d e r to f i n d a r e l a t i o n between t h e e l e c t r o n a c c e p t i n g p r o p e r t i e s -of a l i g a n d a n d i t s s t e r i c a l r e q u i r e m e n t s on one s i d e a n d t h e d e g r e e o f i n t e r m o l e c u l a r e l e c t r o n e x c h a n g e on t h e o t h e r t h e l i g a n d s h a v e t o be v a r i e d s y s t e m a t i c a l l y o v e r a w i d e r a n g e b u t i n s m a l l s t e p s . F o r t h i s r e a s o n we p r e p a r e d and i n v e s t i g a t e d a g r o u p o f i s o n i t r i l e d e r i v a t i v e s t h e t y p e [Pt (CNR)i|] [ P t C l i j ] w i t h R = a r y l a n d v a r i e d t h e l i g a n d s s y s t e m a t i c a l l y by u s i n g d i f f e r e n t s u b s t i t u t e d i s o n i t r i l e s (18) . As e x p e c t e d on t h e b a s i s o f t h e s i m p l e m o d e l , e l e c t r o n w i t h d r a w i n g g r o u p s had an e f f e c t of strengthening the m e t a l - m e t a l i n t e r a c t i o n s and hence t h e c o - o p e r a t i v e p r o p e r t i e s w h i l e e l e c t r o n d o n a t i n g s u b s t i t u e n t s on t h e l i g a n d a r e w e a k e n i n g t h e s e i n t e r a c t i o n s . T h i s i s e a s i l y shown by studying t h e o p t i c a l p r o p e r t i e s o f t h e compounds. Complexes with strongly e l e c t r o n accepting groups, decrease of AE, a b s o r b s t r o n g l y i n the r e d p a r t o f t h e v i s i b l e s p e c t r u m and a r e deep b l u e o r v i o l e t i n t h e s o l i d s t a t e . Complexes w i t h d o n a t i n g i s o n i t r i l e groups a r e a b s o r b i n g i n t h e b l u e p a r t and a p p e a r y e l l o w f o r t h i s r e a s o n . By u s i n g b u l k y i s o n i t r i l e l i g a n d s t h e inter a c t i o n s b e t w e e n t h e m e t a l i o n s a r e d e c r e a s e d as w e l l but t h i s e f f e c t i s m i n o r compared t o the " e l e c t r o n i c " e f f e c t . Complexes o f t h i s t y p e , w i t h b u l k y and d o n a t i n g l i g a n d s , l o o k y e l l o w g e n e r a l l y w h i l e the ones w i t h s m a l l a c c e p t i n g l i g a n d s l o o k b l u e , show a t y p i c a l c o p p e r - l i k e m e t a l l i c l u s t r e which i s l i n e a r l y p o l a r i z e d x

2

2


IONS

2 -

2 +

1

2

i |



21.

Linear

ADERJAN ET AL.

Chain

Complexes

321

p a r a l l e l to the needle a x i s of the c r y s t a l s (18). The same s y s t e m a t i c change i n s o l i d s t a t e p r o p e r t i e s w i t h the v a r i a t i o n i n e q u a t o r i a l l i g a n d s can be observed i n planar chelatodicarbonylrhodium(I) and i r i d i u m ( I ) compounds ( g r o u p 4) some o f w h i c h c r i s t a l l i z e i n c o l u m n a r s t a c k s ( 9 ) . The a n i s o t r o p i c p h y s i c a l p r o p e r t i e s of these s o l i d s r e s u l t i n g from intermolecul a r i n t e r a c t i o n s , w h i c h w e r e the s u b j e c t o f i n t e n s e i n v e s t i g a t i o n s s e v e r a l y e a r s ago ( 1 9 ) , c a n be v a r i e d by c h e m i c a l s y n t h e s i s . C o m p l e x e s o f t h i s t y p e , e. g . o f s t o i c h i o m e t r y I r ( C 0 ) 2 ( L - L ) , c a n be o b t a i n e d e a s i l y by s u b s t i t u t i n g one c a r b o n y l g r o u p a n d a c h l o r i d e l i g a n d i n I r ( C O ) - j C l . The s y n t h e s i s p r o c e e d s e s p e c i a l l y w e l l i f the t r i c a r b o n y l c h l o r o i r i d i u m ( I ) i s r e a c t e d with the " T r i t o n B" ( t r i p h e n y l b e n z y l a m m o n i u m h y d r o x i d e ) s a l t o f the l i g a n d (10). Some c o n c l u s i o n s u p o n t h e i n t e r m o l e c u l a r i n t e r a c t i o n s c a n be d r a w n by l o o k i n g a t t h e i r o p t i c a l a b s o r p t i o n s p e c t r a . The i n t e r a c t i o n s a r e d i m i n i s h e d w i t h i n c r e a s i n g s i z e o f t h e l i g a n d s a n d by s u b s t i t u t i n g d o n a t i n g g r o u p s and t h e absorption i s s h i f t e d t o s h o r t e r wave l e n g t h s . The e l e c t r i c c o n d u c t i v i t y i s d e c r e a s e d d r a s t i c a l l y i n compounds w i t h l a r g e o r g a n i c d y e b a s e s a s l i g a n d s ( 2 0 ) . I n some c a s e s w i t h v e r y l a r g e l i g a n d s e v e n m o d i f i c a t i o n c h a n g e s c a n be o b s e r v e d , w h i c h i n d i c a t e t h a t the i n t e r a c t i o n s are not very s t r o n g i n t h e s e s o l i d s and t h a t t h e l a t t i c e s t r u c t u r e i s d e t e r m i n e d by t h e l a r g e o r g a n i c l i g a n d m o l e c u l e s . The conc l u s i o n t h a t one o f t h e m o d i f i c a t i o n s crystallizes w i t h o u t e s s e n t i a l i n t e r m o l e c u l a r i n t e r a c t i o n s i s drawn from the d i f f e r e n c e s i n the o p t i c a l s p e c t r a of these s y s t e m s . The o p t i c a l a b s o r p t i o n s p e c t r a o f t h e two mod i f i c a t i o n s a r e q u i t e d i f f e r e n t . One o f t h e m shows a b r o a d band i n the " r e d " which i s t o t a l l y absent i n t h e s e c o n d m o d i f i c a t i o n , w h i c h no l o n g e r h a s s i g n s o f c o l l e c t i v e e l e c t r o n b e h a v i o u r (11) . We a r e i n t h e p r o c e s s of completing the X-ray s t r u c t u r e determinat i o n of the d i f f e r e n t m o d i f i c a t i o n s . The Môfèbauer e f f e c t i s a m o r e s e n s i t i v e s p e c t r o s c o p i c probe f o r the i d e n t i f i c a t i o n o f intermolecular i n t e r a c t i o n s and t h e more a c c u r a t e c l a s s i f i c a t i o n o f t h e i r s t r e n g t h . I t works q u i t e w e l l w i t h i r i d i u m (193i ) d shown by o u r r e s u l t s , t h e i s o m e r s h i f t s as w e l l as t h e q u a d r u p o l e s p l i t t i n g s d e p e n d s t r o n g l y on t h e s t r e n g t h o f t h e i n t e r m o l e c u l a r i n t e r a c t i o n s a l o n g the m e t a l c h a i n s ( 2 1 , 22). T h i s i s summarized i n f i g u r e 2 w h i c h shows t h a t a v e r y c o n s i s t e n t l i s t o f s h i f t s i s t obtained. Negative isomer s h i f t s , r e l a t i v e t o i r i d i u m m e t a l as t h e s t a n d a r d , a r e f o u n d i n s o l i d s r

a

n

a

s


322

INTERACTIONS

BETWEEN

METAL

IONS


EXTENDED

Figure 2. hidentate,

Ir-Mossbauer shifts of Ir(L-L)(CO) and IrL'L(CO) compounds (l^L — uninegative, L = neutral, unidentate U = unidentate, uninegative ligand. Arrows connect different modifications of one compound). 193

2

t



21.

ADERJAN ET A L .

Linear

Chain

Complexes

323

w h i c h give c l e a r e v i d e n c e to strong intermolecular i n t e r a c t i o n s i n t h e s o l i d s t a t e . The compounds w i t h on l y weak m e t a l - m e t a l i n t e r a c t i o n s show p o s i t i v e s h i f t s and q u i t e l a r g e q u a d r u p o l e s p l i t t i n g s . E s p e c i a l l y i n t e r e s t i n g a r e t h e d a t a o f t h e s e com p l e x e s w h i c h c r y s t a l l i z e i n two m o d i f i c a t i o n s , one of w h i c h o n l y c o n t a i n s c o l u m n a r s t a c k s . As e x p e c t e d , t h e i s o m e r s h i f t s o f t h e m o d i f i c a t i o n w i t h o u t any s i g n o f co-operative e l e c t r o n behaviour are l a r g e r than those o f the deeply c o l o r e d form c r y s t a l l i z i n g i n columnar s t a c k s . The q u a d r u p o l e s p l i t t i n g s a r e s m a l l e r f o r t h e compounds w i t h s t r o n g i n t e r m o l e c u l a r i n t e r a c t i o n s growing l a r g e r with d e c r e a s i n g i n f l u e n c e of the a x i a l l i g a n d s a s p r e d i c t e d by t h e s i m p l e c r y s t a l f i e l d mo d e l . By c o m p a r i n g t h e Moftbauer r e s u l t s w i t h t h o s e o f o t h e r s p e c t r o s c o p i c m e t h o d s , i t seems t h a t the Μδβb a u e r e f f e c t i s a w e l l s u i t e d method i n the case o f i r i d i u m complexes t o c l a s s i f y i n t e r m o l e c u l a r i n t e r a c t i o n s i n l i n e a r chain metal complexes. A s i m i l a r r e l a t i o n between s o l i d s t a t e p r o p e r t i e s o n one s i d e a n d s t e r i c a l a n d e l e c t r o n i c l i g a n d p a r a m e t e r s o n t h e o t h e r h a n d c a n be f o u n d i n t h e "dioximato" c o m p l e x s e r i e s . N u m e r o u s c o m p l e x e s o f d " i o n s w i t h these l i g a n d s were d e s c r i b e d i n t h e p a s t (4, 2 3 ) . E s p e c i a l l y s t r o n g i n t e r a c t i o n s i n these s o l i d s are found i n the Bis(1,2-benzoquinonedioximato)metal(II) s p e c i e s the l i g a n d o f w h i c h i s r e l a t i v e l y s m a l l and i s c a p a b l e of d e l o c a l i z i n g metal d-electrons (24). These examples prove t h a t even d°-ions i n l i n e a r m e t a l c h a i n complexes are capable o f s t r o n g i n t e r a c t i o n s g i v i n g r i s e t o c o - o p e r a t i v e e l e c t r o n b e h a v i o u r as p o i n t e d o u t by i n v e s t i g a t i o n s o f t h e i r o p t i c a l s p e c t r a . E s p e c i a l l y t h o s e c a n d i d a t e s w h i c h have o n l y s m a l l and strongly e l e c t r o n accepting ligands are capable of v e r y s t r o n g i n t e r a c t i o n s a n d show c o l l e c t i v e e l e c t r o n b e h a v i o u r i n one d i m e n s i o n s u c h a s h i g h c o n d u c t i v i t y and l o n g w a v e l e n g t h a b s o r p t i o n s . T h e r e f o r e , i t seems p o s s i b l e to s y n t h e s i z e ld-metals even with ions" i f a p p r o p r i a t e l i g a n d s are used. I r ( C Q ^ C l which con s i d e r e d i n o u r o p i n i o n t o be a p u r e d ° - c o m p o u n d , i s a n i m p r e s s i v e e x a m p l e t h a t t h e e n e r g y gap ΔΕ c a n be r e d u c e d v e r y much by u s i n g e l e c t r o n a c c e p t i n g g r o u p s a n d t h a t t h e d . c . - c o n d u c t i v i t y c a n be r a i s e d by u s i n g small ligands to almost m e t a l i c behaviour. Nevertheless the i n t e r m e t a l l i c i n t e r a c t i o n s i n a l l o f t h e s e d" t r a n s i t i o n m e t a l complexes a r e not s t r o n g enough t o overcome t h e s t e r i c a l p r o b l e m s and a d.c.-conductivity corresponding to a m e t a l l i c state has not b e e n a c h i e v e d . E s p e c i a l l y , i f u s i n g l a r g e and p o l a r i z e a b l e o r g a n i c dye m o l e c u l e s w h i c h a r e necessary


324

EXTENDED

INTERACTIONS

BETWEEN

METAL

IONS

i n t h e s e a r c h f o r a " L i t t l e m o d e l compound" ( 2 5 , 26) the m o b i l i t y o f charge c a r r i e s i s decreased considera b l y . T h e r e f o r e we t r i e d t o s y n t h e s i z e new "mixed v a l e n c e " s o l i d s by o x i d i z i n g d ^ - c o m p o u n d s .


VI.

Preparation

of

"Mixed V a l e n c e "

Solids

The r e s u l t s o f o x i d a t i o n r e a c t i o n s on d ^ l i n e a r c h a i n m e t a l c o m p l e x e s w e r e s t u d i e d t h o r o u g h l y Jbr t h e tetrakis(cyano)platinum(II)complexes a n d some o x a l a t o d e r i v a t i v e s . The f i r s t i n v e s t i g a t i o n s w e r e c a r r i e d o u t more t h a n 100 y e a r s ago a n d t h e r e s u l t s o f a l l o f t h e w o r k a r e w e l l known a n d a r e s u m m a r i s e d (3) » One i m p o r t a n t q u e s t i o n r e m a i n s t o be a n s w e r e d : "Why does the o x i d a t i o n o f o t h e r square p l a n a r platin u m ( I I ) compounds, c r y s t a l l i z i n g i n c o l u m n a r s t a c k s , not p r o c e e d t o "mixed v a l e n c e " o n e - d i m e n s i o n a l m e t a l s ? " T h i s c a n be a n s w e r e d by i n v e s t i g a t i n g t h e a s s o c i a t i o n r e a c t i o n s i n s o l u t i o n , which lead to l i n e a r chains. This " p i l i n g u p " - r e a c t i o n i s e s s e n t i a l l y a donora c c e p t o r a s s o c i a t i o n between a square p l a n a r platin u m ( I I ) d o n o r and a s o l v a t e d p l a t i n u m ( I V ) a c c e p t o r . The r e a c t i o n i s p r e v e n t e d i f s o l v e n t m o l e c u l e s o c c u p y the " a x i a l p o s i t i o n s " i n the s t r o n g l y a c c e p t i n g platin u m ( I V ) m o i e t y , w h i c h c a n n o t be r e m o v e d by d o n a t i n g p l a t i n u m ( I I ) s p e c i e s . A chain i s obtained i f the a x i a l l y b o u n d s o l v e n t m o l e c u l e s c a n be s u b s t i t u t e d by t h e d o n a t i n g p l a t i n u m ( I I ) s p e c i e s , t h a t means, i f t h e following r e a c t i o n s proceed to a s s o c i a t e s : [CI · P t I V ( C N ) 4 · H 0 ] + [H 0 · P t ( H ) ( C N ) 4 · H 0] 1=* 2

2

2

[H 0 2

· Pt^

1 1

) (CN)

2

I V

· Pt (CN)2j

4

[H 0-Pt(H)(CN)4.Pt 2

[H 0-PtH(CN)i|.Pt

I V

2

I V

· H 0] "

(CN)4.H 0] " 2

(CN)

i |

2

+ H 0

2

2

+

2

CI";

+ [ H 0 · P t ( CN ) 4 * H 0 ] 2

2

2

.PtII(CN)i -H 0] " + 2H 0; 4

1 |

2

2

T h i s t y p e o f r e a c t i o n does t a k e p l a c e i n aqueous s o l u t i o n i n t h e c a s e o f [Pt (CN)ij] ~ and [ P t ( C 0 j j ) ] " i o n s b u t i s p r e v e n t e d i n t h e same s o l v e n t when u s i n g comp l e x e s o f the type P t C l ^ " o r [Pt ( N H j ) 4] , b e c a u s e e i t h e r the r e d u c e d form o f the o x i d i z i n g agent (mostl y h a l o g e n i d e i o n s ) or the s o l v e n t m o l e c u l e s are bonded v e r y c o v a l e n t l y o n t o t h e a x i a l p o s i t i o n s o f t h e platinum(IV) acceptor. I f t h i s assumption i s c o r r e c t , t h e o x i d a t i o n s h o u l d p r o c e e d t o " m i x e d v a l e n c e " comp o u n d s o n l y i f t h e r e a c t i o n c a n be c a r r i e d o u t i n n o n d o n a t i n g o x i d i z i n g s o l v e n t s . The medium c o u l d be h a l f concentrated s u l f u r i c a c i d . The r e d K P t C l j | , t h e y e l low P t ( N H - C H - C H - N H ) C l a n d t h e g r e e n Magnus S a l t c a n be o x i d i z e d t o d e e p l y c o l o u r e d compounds w i t h a 2

2

2

2

2

2 +

2

1

2

2

2

2

2


Â


21.

ADERjAN E T A L .

Linear

Chain

Complexes

325

remarkable red m e t a l l i c l u s t r e i n h a l f concentrated s u l f u r i c a c i d . C h e m i c a l and p h y s i c a l e v i d e n c e clearly p r o v e s t h a t t h e s e compounds a r e m i x e d v a l e n c e solids. S i n c e t h e r e a c t i o n i s a h e t e r o g e n o u s one a n d f o r t h i s r e a s o n o n l y p o w d e r s c o u l d be o b t a i n e d ( 2 7 ) t h i s procedure i s not a p p r o p r i a t e i n the s y n t h e s i s of l d - m e t a l l i c s i n g l e c r y s t a l s . We a r e s t i l l l o o k i n g f o r o t h e r b e t t e r s u i t e d s o l v e n t s and o x i d i z i n g a g e n t s . On t h e o t h e r h a n d we h a v e c o n t i n u e d o u r search f o r "mixed v a l e n c e " s o l i d s w i t h c e n t r a l m e t a l s o t h e r than platinum. In order to obtain p a r t i a l l y o x i d i z e d s o l i d s o n l y c o - o r d i n a t i o n compounds, t h e l i g a n d s o f w h i c h s h o u l d be s t a b l e a g a i n s t o x i d a t i o n by h a l o g e n s o r s i m i l a r s u b s t a n c e s c o u l d be u s e d a s s t a r t i n g m a t e r i a l s . As shown by many i n v e s t i g a t i o n s d i o x i m a t o l i gands a r e c h e m i c a l l y v e r y s t a b l e and g i v e m e t a l column a r s t a c k s . " M i x e d v a l e n c e " s o l i d s i s o l a t e d by o x i d a t i o n o f B i s ( l , 2 - d i p h e n y l g l y o x i m a t o ) - n i c k e l ( I I ) and palladium(II) h a v e b e e n known f o r a l o n g t i m e b u t were not r e c o g n i z e d as s t r o n g l y i n t e r a c t i n g m e t a l c h a i n s . In f a c t the c r y s t a l s c o n t a i n stacks of pancaked metal c o m p l e x e s ( w i t h a n a v e r a g e o x i d a t i o n number o f 2.33 f o r t h e c e n t r a l m e t a l i o n ) and l i n e a r c h a i n s o f I j ~ u n i t s p a r a l l e l to these s t a c k s . A s t r u c t u r e very s i m i l a r t o t h e one f o u n d i n t h e b l u e s t a r c h - i o d i n e a d d u c t s was p r o p o s e d . The e s s e n t i a l d i f f e r e n c e i s t h a t b o t h s t a c k s c o u l d show c o l l e c t i v e e l e c t r o n b e h a v i o u r . This i s very i n t e r e s t i n g with respect to the p r e d i c t i o n t h a t m o b i l e e l e c t r o n s on two p a r a l l e l n o n - d e g e n e r a t e conduction spines could i n t e r a c t with each other i n a m a n n e r p r o p o s e d by L i t t l e f o r an e x c i t o n i c h i g h - t e m p e r a t u r e s u p e r c o n d u c t o r ( 2 8 ) . A s i m i l a r s o l i d c o u l d be o b t a i n e d by o x i d i z i n g b i s ( 1 , 2 - b e n z o q u i n o n e d i o x i m a t e ) p a l l a d i u m ( I I ) and n i c k e l ( I I ) i n d i c h l o r o b e n z e n e to mixed v a l e n c e s p e c i e s which d i f f e r i n t h e i r s o l i d s t a t e p r o p e r t i e s c o n s i d e r a b l y from t h e i r u n o x i d i z e d parent c o m p o u n d s . The r e s u l t s o f X - r a y a n a l y s i s s o f a r s u g g e s t t h a t l i n e a r m e t a l and i o d i n e c h a i n s r u n p a r a l l e l t h r o u g h t h e l a t t i c e o f t e t r a g o n a l s y m m e t r y a s shown s c h e m a t i c a l l y i n f i g u r e 3. F u r t h e r m o r e we h a v e u s e d a n o t h e r w e l l - k n o w n t y p e o f r e a c t i o n t o come t o m i x e d v a l e n c e s o l i d s : t h e s o c a l l e d 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 s . This type of r e a c t i o n c o u l d p o s s i b l y be u s e d f o r p i l i n g up l i n e a r met a l c h a i n s by a d d i n g a t e t r a k i s ( a r y l i s o n i t r i l e ) r h o dium(III) species to a t e t r a k i s ( a r y l i s o n i t r i l e ) rhod i u m ( I ) compound i n t h e f o l l o w i n g m a n n e r :



326

EXTENDED

INTERACTIONS

BETWEEN

METAL

IONS

Figure 3. Schematic of two non-degenerate conduction spines in the lattice of bis(1,2-benzoquinonedioximato)iodonickel (II, IV)

^7 ^7 ^7

RNCRNC "

Rh I

CNR CNR

I RNC RNC

Rh

CNR • CNR

I Figure 4. Structure "mixed valence'' solid methylphenylisonitrile

proposed for the diiodotetrakis(2fi-di)rhodium(I III ). y

RNC RNC

I Rh

I

•CNR CNR

I RNC RNC

Rh

CNR CNR

I RNC RNC

I Rh I

I


- CNR • CNR


Figure

5.

Molecular structure cation in

of the μ-iodobis [tetrakis(phenylisonitrilejcobaltfll)] diiodotetrakis(phenylisonitrile)cobalt(II)


+

328

EXTENDED

2[Rh(CNR)Z|]+ +

INTERACTIONS

METAL

IONS

+

[Rh(CNR)4l ] *==a 2

[I-Rh(CNR) -Rh(CNR)4-I]2+ i|

+

[Rh(CNR)i|]

[I-Rh(CNR) -Rh(CNR)i -Rh(CNR)i|-I]3 i |


BETWEEN

+

+

|

By m i x i n g t h e 2 , 6 - d i m e t h y l p h e n y l i s o n i t r i l e r h o d i u m ( I ) and r h o d i u m ( I I I ) d e r i v a t i v e s i n c h l o r o f o r m a s u d d e n change o f c o l o r i s observed t u r n i n g from a y e l l o w - r e d t o d a r k b l u e . From t h i s s o l u t i o n a v i o l e t s o l i d w i t h a s t r i k i n g l i n e a r l y p o l a r i z e d m e t a l l i c l u s t r e c a n be o b t a i n e d . W h e t h e r t h e compound c o n t a i n s d i r e c t l y b o u n d m e t a l - m e t a l c h a i n s o r an i o d i n e b r i d g e d M - I - M - I l a t t i c e c a n be d e c i d e d o n l y a f t e r t h e X - r a y determina t i o n has b e e n c o m p l e t e d . The p r e l i m i n a r y s p e c t r o s c o p i c d a t a i n d i c a t e an i o d i d e - b r i d g e d s t r u c t u r e (7) as i n d i c a t e d s c h e m a t i c a l l y i n f i g u r e 4. F i n a l l y we w o u l d l i k e t o p r e s e n t j u s t one r e s u l t w h i c h we o b t a i n e d o n o u r s e a r c h f o r l i n e a r c h a i n com p o u n d s c o n t a i n i n g d 7 - m e t a l i o n s . A t y p i c a l and v e r y stable i o n with t h i s e l e c t r o n i c c o n f i g u r a t i o n i s co b a l t ( I I ) . The e a r l i e r r e p o r t o f M a l a t e s t a t h a t d i i o d o t e t r a k i s ( a r y l i s o n i t r i l e ) c o b a l t ( I I ) compounds c a n be i s o l a t e d i n two c r y s t a l l i n e m o d i f i c a t i o n s o f w h i c h one i s d i a m a g n e t i c a n d shows a r e m a r k a b l e m e t a l l i c l u s t r e (29) p r o m p t e d us t o d e t e r m i n e t h e e x a c t s t r u c t u r e o f one o f t h e s e compounds ( 3 0 ) . T h e m o l e c u l a r s t r u c t u r e o f t h e t e t r a k i s ( p h e n y l i s o n i t r i l e ) c o b a l t ( I I ) i s shown i n f i g u r e 5 which i s i n f a c t μ-iodo-bis [ i o d o t e t r a k i s ( p h e n y l i s o n i t r i l e ) c o b a l t ( I I ) ] i o d i d e . The l i n e a r l y p o l a r i z e d o p t i c a l absorption of the s o l i d corresponds to a t r a n s i t i o n a l o n g t h e I - Co - I - Co - I h e a v y a t o m chains a l l o f which r u n p a r a l l e l t o each o t h e r . T h o u g h a p u r e l i n e a r c h a i n d^-compound w o u l d be i d e a l f o r our purposes t h e s y n t h e s i s o f such s o l i d s seems t o b e v e r y d i f f i c u l t b e c a u s e o f t h e s t r o n g L e w i s a c i d a c t i v i t y o f t h e s e compounds. Acknowledgements T h i s work was s u p p o r t e d by D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t and Fonds d e r Chemischen I n d u s t r i e .


ADERJAN E T A L .

21.

Linear

Chain

Complexes

329

"Literature Cited," Zeller, H.R., A d v . Solid S t a t e P h y s . , ( 1 9 7 3 ) , Vol. X I I I 2 Garito, A.F., Heeger, A.J., (preprint) 3 K r o g m a n n , K., Angew. Chem., ( 1 9 6 9 ) , 8 1 , 10 4 Thomas, T.W., Underhill, A . E . , Chem. S o c . R e v . , 1

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Gitsel,

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H.J.,

Lorentz,

R., Rupp, H.H.,

( 1 9 7 3 ) , 28b, 161

Dart, J.W., Lloyd, M.K., M a s o n , R., M c C l e v e r t y , J . A . , J.C.S. Dalton, ( 1 9 7 3 ) , 2039 Baumann, D., (1974),Dissertation, Univ.Heidelberg Mehran, F., Scott, B.A., Phys. Rev. Lett., (1973), 31, 99 Bailey, N.A., Coates, E.U., Robertson, G.B., Bonati, F . , U g o , R., Chem. Commun., ( 1 9 6 7 ) , 1041 Aderjan, R., Breer, H., Keller, H . J . , R u p p , H.H.,

( 1 9 7 3 ) , 28b, 164

Z.Naturforsch., 11

Aderjan, R., Keller, 28b, 500 12 Hieber, W., Lagally,

H.J.,

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(1973),

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13 B e n s o n , R . E . , U.S. Patent, ( 1 9 6 6 ) , 3-255-195 14 Malatesta, L . , Canziani, F . , J. Inorg. Nucl. Chem.,

(1961), 19, 81

15

Keller,

H.J.,

Seibold,

K., J. Amer.

Chem. Soc.,

(1971), 93, 1309 Dickinson, G.E., J. Amer. Chem. Soc., ( 1 9 2 2 ) , 44, 2404 17 Fritz, H.P., Keller, H.J., Z.Naturforsch., (1965), 20b, 1145 18 Lorentz, R., ( 1 9 7 4 ) , Dissertation, Univ.Heidelberg 19 Monteith, K.L., Ballard, L . F . , Pitts, C.G., Klein, B.K., Slifkin, L.M., C o l l m a n , J . P . , Solid S t a t e

16

Comm., ( 1 9 6 8 ) , 6, 301 20

Aderjan, R., Keller, H . J . , R u p p , H.H., (submitted for publication) 21 Aderjan, R., ( 1 9 7 3 ) , Dissertation, Univ.Heidelberg 22 Aderjan, R., Keller, H . J . , R u p p , H.H., W a g n e r , F . , W a g n e r , U., (to be published) 23 B a n k s , C.V., B a r n u m , D.W., J. Amer. Chem. S o c . ,

( 1 9 5 8 ) , 80, 3579

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( 1 9 7 4 ) , 10, 467

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Μ., Lett.,

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( 1 9 7 2 ) , 41, 1011


330

27

EXTENDED

Gitzel,

W.,

Z.Naturforsch., 28 29

Keller,

INTERACTIONS B E T W E E N

H . J . , Rupp, H.H.,

J.

Seibold,

IONS

K.,

( 1 9 7 2 ) , 27b, 365

Little, W.A., (private communication) Malatesta, L., Isocyanide Complexes o f

(1969),

METAL

Wiley,

Metals,

London H . J . , W e i s s , J.,


30 Baumann, D., E n d r e s , Η . , Keller, J . C . S . Chem. Comm., ( 1 9 7 3 ) , 853


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