Unusual Properties Associated with One ... - ACS Publications

2 Unusual Properties Associated with One-Dimensional Inorganic Complexes J O E L S. M I L L E R

Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch002

Physical and Chemical Sciences Laboratory, Webster Research Center, Xerox Corp., 800 Phillips Rd.-114, Webster, N . Y. 14580

In recent years there has been increased interest in inorganic and organic materials which exhibit highly anisotropic properties arising from a one-dimensional or pseudo-one-dimensional structure in the solid state. Besides being pleochroic, such one-dimensional materials may exhibit cooperative magnetic interactions (ferro and antiferromagnetic coupling) as well as unusual electrical properties (e.g. high conductivity and low thermal electric power). The unusual properties of 1-D systems are surveyed while focusing is on the structural and electronic features of the materials to aid in predicting new classes of materials which may exhibit unusual electrical, magnetic, and optical properties. These properties are discussed in terms of transition metal (row and group), oxidation state, geometry, ligand field strength, stoichiometry, etc. / ^ \ n e - d i m e n s i o n a l ( l - D ) systems (1, 2, 3, 4, 5, 6) are best defined i n terms of t h e i r a n i s o t r o p i c e l e c t r i c a l , m a g n e t i c , a n d o p t i c a l properties. A l l n o n c u b i c crystals w i l l e x h i b i t s u c h a n i s o t r o p i c properties b y v i r t u e of the s y m m e t r y , b u t for this discussion a 1-D system is defined b y a n intensive p r o p e r t y w h i c h is p r o n o u n c e d i n a single d i r e c t i o n w i t h respect to the r e m a i n i n g o r t h o g o n a l directions—e.g. t h e e l e c t r i c a l c o n d u c t i v i t y ( 7 ) a n d o p t i c a l (8) a n d reflectance ( 9 ) spectra of K P t ( C N ) B r . 3 o o • 3 H 0 (10, 11). T h e s e p r o n o u n c e d a n i s o t r o p i c properties arise f r o m stronger i n t e r m o l e c u l a r interactions i n one d i m e n s i o n i n the c r y s t a l t h a n i n the r e m a i n i n g directions. I n the context of the b r o a d subject of i n o r g a n i c c h e m i s t r y , the complexes w h i c h e x h i b i t strong a n i s o t r o p i c p r o p e r ties are r e l a t i v e l y f e w i n n u m b e r , a n d , h a v i n g b e e n s t u d i e d i n d e t a i l o n l y r e c e n t l y , t h e y are classified as u n u s u a l . T h e most extensively s t u d i e d 1-D i n o r g a n i c c o m p l e x K P t ( C N ) B r o . 3 o o * 3 H 0 , is d e p i c t e d i n F i g u r e 1. 2

4

2

2

4

2

18 King; Inorganic Compounds with Unusual Properties Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

0


2.

MILLER

One-Dimensional Complexes

19

T h i s p a p e r focuses o n t h e u n u s u a l p r o p e r t i e s associated w i t h

1-D

i n o r g a n i c complexes w h i c h m a k e s t h e m w o r t h y of s p e c i a l s t u d y . A l t h o u g h a v a r i e t y of p r o p e r t i e s are u n u s u a l because 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 the s o l i d , o n l y those m o s t f a m i l i a r to i n o r g a n i c chemists are d i s c u s s e d — n a m e l y , t h e o p t i c a l , m a g n e t i c , a n d e l e c t r i c a l properties. f a m i l i a r to p h y s i c i s t s (2, 3, 6)—e.g.,

t e r i n g , piezoresistance, a n d specific h e a t — a r e n o t discussed. s p e c i a l features

of s t r u c t u r e , s t o i c h i o m e t r y ,

o x i d a t i o n state a r e d i s c u s s e d

Topics more

t h e r m o e l e c t r i c p o w e r , n e u t r o n scatligand

field

In addition, strength, a n d

since they f r e q u e n t l y y i e l d clues t h a t a

complex m a y exhibit unusual properties.

T h e s u r v e y is n o t i n t e n d e d to

b e exhaustive b u t rather to g i v e a n i n d i c a t i o n of w h i c h p r o p e r t i e s m o s t u s e f u l i n the c h a r a c t e r i z a t i o n of n e w

are

and, i n particular, highly

c o n d u c t i n g 1-D c o m p l e x e s . T h e f o l l o w i n g is a case h i s t o r y of the o n e - d i m e n s i o n a l

inorganic

c o m p l e x , K ^ o . 5 l r ( C O ) C l 2 , w h i c h exhibits h i g h c o n d u c t i v i t y at r o o m t e m 2

perature.

T h i s c o m p l e x e x h i b i t s a v a r i e t y of u n u s u a l p r o p e r t i e s

which

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

f o r its s t r u c t u r e .

T h i s m a t e r i a l serves as a n

i n s t r u c t i v e e x a m p l e to p o i n t o u t s e v e r a l features w h i c h m a k e the c o m p l e x w o r t h y of d e t a i l e d s t u d y .

T o date, the d e t a i l e d s t u d y of its e l e c t r i c a l ,

m a g n e t i c , a n d o p t i c a l p r o p e r t i e s has not b e e n r e p o r t e d .

King; Inorganic Compounds with Unusual Properties Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

20

INORGANIC

COMPOUNDS

I n 1961 M a l a t e s t a a n d C a n z i a n i (12)

WITH

UNUSUAL PROPERTIES

r e p o r t e d the r e a c t i o n of potas-

s i u m h e x a c h l o r o i r i d a t e ( I V ) w i t h c a r b o n m o n o x i d e a n d a c o p p e r catalyst a b o v e 1 0 0 ° C at h i g h - p r e s s u r e to y i e l d K I r ( C O ) C l 2

4

and K I r ( C O ) C l 4 . ,

4

2

4

8

w h i c h suggests a m i x e d v a l e n t character for the m a t e r i a l s . T h e s e

com-

plexes h a d a m e t a l l i c luster a n d w e r e r e p o r t e d to b e d i a m a g n e t i c i n the s o l i d a n d i n acetone. T h e b r o m o analogs, K I r ( C O ) B r 2

4

4

and K I r ( C O ) 2

2

4

B r , w e r e also p r e p a r e d as w e r e a v a r i e t y of salts w i t h different cations. 5

T h e former bromo complex exhibited v agrees w i t h the v

co

at 2092 a n d 2053 c m "

co

which

1

absorptions of v a r i o u s h a l o c a r b o n y l I r a n d I r 1

com-

1 1

plexes. A n almost c o m p l e t e a n d c o n t i n u o u s I R a b s o r p t i o n was also n o t e d w h i c h p r e s u m a b l y arises f r o m the h i g h r e f l e c t i v i t y of the m a t e r i a l . T h e authors f o r m u l a t e d d i n u c l e a r structures to a c c o u n t for t h e s t o i c h i o m e t r y Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch002

a n d the t e r m i n a l c a r b o n y l groups.

H o w e v e r , these structures d o

not

a c c o u n t f o r the t w o c a r b o n y l absorptions i n the I R , the solid-state a n d s o l u t i o n d i a m a g n e t i s m , or the m e t a l l i c color of these complexes

which

is i n contrast w i t h the colors of other i r i d i u m complexes. A d e c a d e later C l e a r e a n d G r i f f i t h (13) concentrated

r e p o r t e d that the r e a c t i o n of

h y d r o h a l i c a n d f o r m i c acids w i t h

hexachloroiridate(IV)

results i n the f o r m a t i o n of d i a m a g n e t i c n e e d l e crystals of

[Ir (CO) X ] " 2

4

4

1

s t o i c h i o m e t r y w h i c h e x h i b i t m e t a l l i c reflections. I n a c c o r d w i t h the w o r k of M a l a t e s t a a n d C a n z i a n i (12),

they p r e p a r e d t h e b r o m o complexes

as

w e l l as complexes c o n t a i n i n g different cations, b u t t h e y d i d not p r e p a r e complexes

containing more than four halides.

T o account for the

ob-

s e r v e d d i a m a g n e t i s m , t h e y p r o p o s e d a p l a n a r t e t r a n u c l e a r structure b a s e d o n the s t r u c t u r e of the isoelectronic R e ( C O ) i 4

I n 1972 B u r a v o v et al. four-probe (CO) Cl 4

4 8

(15)

6

2 +

r e p o r t e d the

ion

(14).

temperature-dependent

p o l y c r y s t a l l i n e d c c o n d u c t i v i t y of K I r ( C O ) C l 2

4

4

and K I r 2

p r e p a r e d b y the m e t h o d of M a l a t e s t a a n d C a n z i a n i

B o t h complexes

2

(12).

h a d high conductivity, w h i c h implies intermolecular

i n t e r a c t i o n s a n d a p a r t i a l l y o x i d i z e d character i n the s o l i d . T h e p r e v i o u s l y p r o p o s e d d i n u c l e a r a n d t e t r a n u c l e a r structures l a c k 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 n d thus m u s t b e d i s c o u n t e d . R e c e n t l y K r o g m a n n et

al. p o s t u l a t e d a cation-deficient,

partially

o x i d i z e d f o r m u l a t i o n for this m a t e r i a l , K ~ . 5 l r ( C O ) C l , a n d a c o l u m n a r 0

s t r u c t u r e i n the s o l i d (16).

2

2

T h i s o n e - d i m e n s i o n a l s t r u c t u r e is consistent

w i t h the o b s e r v e d d i a m a g n e t i s m , s t o i c h i o m e t r y , I R spectra, d c t i v i t y , a n d v i s u a l a p p e a r a n c e of the complexes.

conduc-

P r e l i m i n a r y powder x-ray

d a t a s u p p o r t this f o r m u l a t i o n w i t h a short 2.86 A I r - I r distance.

This

i n f o r m a t i o n sets a basis for the i n t e r p r e t a t i o n of d e t a i l e d o p t i c a l , e l e c t r i c a l , a n d m a g n e t i c measurements t h a t w i l l h e l p i n f u r t h e r u n d e r s t a n d i n g of the c h e m i s t r y a n d p h y s i c s of o n e - d i m e n s i o n a l i n o r g a n i c complexes. I n a d d i t i o n to a d i s c u s s i o n of the p h y s i c a l p r o p e r t i e s , a short d e s c r i p t i o n of the features i m p o r t a n t i n the u n d e r s t a n d i n g of h i g h l y c o n d u c t i n g


2.

One-Dimensional

MILLER

m a t e r i a l s is presented.

21

Complexes

These include crystallographic,

stoichiometric,

t r a n s i t i o n m e t a l , o x i d a t i o n state, a n d l i g a n d field s t r e n g t h artifacts assoc i a t e d w i t h p a r t i a l l y o x i d i z e d i n o r g a n i c systems. Optical

Properties

S o l u t i o n . I n o r g a n i c complexes t y p i c a l l y e x h i b i t e l e c t r o n i c a b s o r p t i o n spectra i n the U V - v i s i b l e r e g i o n w h i c h are assigned to w -> ir, d-d, charge transfer a n d L —> M c h a r g e transfer absorptions. tions h a v e b e e n r e p o r t e d for f e w e r complexes, assigned to d-d


(17, 18)1

a n d charge transfer absorptions [e.g. of N i ( S C ( C N ) ) ~ 2

2

2

or to i n t r a v a l e n c e transfer ( I V T ) absorptions (19, 20, 21,

t w e e n m e t a l sites of a m i x e d v a l e n t d i m e r [e.g. 3

N e a r - I R absorp-

a n d t h e y are g e n e r a l l y 2

z

22,

a r i s i n g f r o m the F r a n c k - C o n d o n b a r r i e r to e l e c t r o n transfer b e -

23, 24)

(NH )

M —> L

5

5 +

( C o m p l e x I ) , E q u a t i o n 1 (25, 26)].

(HsNJsRuN^O^NRuI n terms of the R o b i n a n d

D a y classification, this is a C l a s s I I m a t e r i a l i n w h i c h the m e t a l ions are d i s t i n g u i s h a b l e (21,

T h e properties

24).

of the m i x e d v a l e n t complexes t y p i f i e d b y

I

are

u n u s u a l b e c a u s e of the n a t u r e of the l o w e n e r g y a b s o r p t i o n , a n d u n u s u a l magnetic

a n d e l e c t r i c a l properties w o u l d b e

e x p e c t e d i f the

discrete

d i m e r molecules i n t e r a c t e d i n the s o l i d . U n u s u a l o p t i c a l , m a g n e t i c , a n d e l e c t r i c a l properties are e x p e c t e d f o r m i x e d v a l e n t c o m p l e x e s of infinite l e n g t h , i.e. g o i n g f r o m R o b i n a n d D a y C l a s s I I I - A to C l a s s I I I - B (21, A n o t h e r u n u s u a l o p t i c a l p r o p e r t y is s o l v a t o c h r o m i s m (27, 28). i n o r g a n i c complexes h a v e s m a l l s o l v e n t - d e p e n d e n t

absorption

24). Most

spectra.

P r o n o u n c e d s o l v a t o c h r o m i s m has n o t b e e n extensively c h a r a c t e r i z e d for i n o r g a n i c c o m p l e x e s i n s o l u t i o n w i t h the e x c e p t i o n of a recent r e p o r t o n the e l e c t r o n i c spectra of a v a r i e t y of d i p o l a r d i t h i o l e n e a - d i i m i n e n i c k e l complexes

(29).

S o l i d . M o s t i n o r g a n i c c o m p l e x e s h a v e solid-state electronic t h a t are v i r t u a l l y s u p e r i m p o s a b l e

w i t h t h e s o l u t i o n spectra.

spectra

F o r these

c o m p l e x e s i t c a n b e stated that the same species ( s a m e electronic s t r u c t u r e s ) exist i n b o t h states. D e v i a t i o n s f r o m the i d e n t i t y of s o l u t i o n a n d solid-state d a t a m a y result f r o m ( a )

e q u i l i b r i a a r i s i n g f r o m association,


22

INORGANIC

COMPOUNDS WITH

UNUSUAL

PROPERTIES

e.g. Ru[S C (CF )2]2PPh3 + 2

or

from

2

PPh

3

different

conformations

Ru(S C (CF ) )(CO)(PPh ) 2

2

3

2

3

^

3

Ru[S C (CF )2]2(PPh3)2 2

i n the

or

actions a r i s i n g f r o m m e t a l - m e t a l b o n d i n g

(b)

N i ( S C ( C N ) 2 ) 2 " (17,

[e.g.

1

2

i n t e r a c t i o n s [e.g.

2

[e.g. M ( H D P G )

[Pt (en)X ] [Pt n

2

z a t i o n of free electrons

I V

18, 3 5 ) ] ,

[e.g.

intermolecular inter-

d i p h e n y l g l y o x i m e ; M — N i (32, 3 3 ) , P d ( 3 2 , 3 3 ) , P t (34))], zation

(30)

3

s o l i d t h a n i n solutions

31)]

(30,

2

2

(H DPG

2

from dimeri-

f r o m infinite m e t a l - h a l o

( e n ) X ] ( 3 6 ) ] , or f r o m t h e d e r e a l i 4

resulting i n a D r u d e behavior

and a

plasma

a b s o r p t i o n c h a r a c t e r i s t i c of a m e t a l [e.g. K P t ( C N ) B r o . 3 o o * 3 H 0 2


4

2

4

0

(2,6,

2

I n aqueous solution K P t ( C N ) B r . 3 o o * 3 H 0

9)"\.

=

2

2

has a n

absorption

s p e c t r u m w h i c h c a n b e d e c o m p o s e d i n t o the s p e c t r a associated w i t h P t n

(CN)

4

2

" a n d f r a r w - P t ( C N ) B r " . N e i t h e r of these latter species i n I V

4

2

2

s o l u t i o n or i n the s o l i d e x h i b i t s the absorptions o b s e r v e d for K P t ( C N ) 2

4

Br .3oo • 3 H 0 i n the s o l i d ( J O ) . 2

0

S i n g l e crystals w h i c h d o not h a v e c u b i c s y m m e t r y s h o u l d e x h i b i t d i c h r o i s m or p l e o c h r o i s m .

P r o n o u n c e d d i c h r o i s m is g e n e r a l l y

w i t h l a r g e a n i s o t r o p i c p r o p e r t i e s a n d is c h a r a c t e r i s t i c of m a t e r i a l s , e.g. M ( C O ) ( a c a c ) ( M — R h , I r (37)

and K P t ( C N ) B r . o o •

2

3 H 0 (8,9).

associated

one-dimensional

2

4

0

3

B a n d semiconductors should have an absorption that corre-

2

s p o n d s to t h e b a n d gap, b u t i t m a y b e difficult to observe. H i g h l y c o n ducting one-dimensional

materials have

a p l a s m a e d g e w h i c h is

the

s i g n a t u r e of a m e t a l l i c state. Color.

I n a d d i t i o n to

white, inorganic

r e m i n i s c e n t of c o m p o n e n t s of the r a i n b o w .

complexes exhibit

colors

A t y p i c a l l y some c o m p l e x e s

h a v e h i g h r e f l e c t i v i t y i n the v i s i b l e r e g i o n a n d a m e t a l l i c luster. A m e t a l l i c l u s t e r n e e d n o t i n d i c a t e a m e t a l l i c state since a p l a s m a a b s o r p t i o n necessary

for t h e existence

crystals of K P t ( C N ) 2

4

of a m e t a l l i c state.

F o r example,

are l i g h t y e l l o w a n d crystals of K P t ( C N ) 2

is

whereas 4

• 3H 0 2

are w h i t e , t h e c r y s t a l faces of K P t ( C N ) B r . 3 o o ' 3 H 0 are c o p p e r c o l o r e d 2

4

2

0

a n d h a v e a p l a s m a a b s o r p t i o n ( a n d m e t a l l i c state) a b o v e 620 n m . faces of s e m i c o n d u c t i n g (38)

Sur-

crystals of I r ( C O ) ( a c a c ) are also m e t a l l i c 2

g o l d i n a p p e a r a n c e a n d h a v e a s t r o n g reflectance at 568 n m (16, 37).

The

e y e c a n n o t d i s t i n g u i s h b e t w e e n the sources of s t r o n g reflectances, a n d a m e t a l l i c luster is a necessary b u t n o t sufficient c o n d i t i o n for a m e t a l l i c state; thus " A l l is n o t g o l d that g l i s t e n s " Magnetic

(39).

Properties

C o o r d i n a t i o n complexes typically exhibit identical magnetic behavior ( d i a m a g n e t i s m or p a r a m a g n e t i s m ) i n b o t h the s o l i d state a n d i n s o l u t i o n . D e v i a t i o n s f r o m s o l u t i o n a n d solid-state m a g n e t i c d a t a suggest e q u i l i b r i a


2.

One-Dimensional

MILLER

[e.g. T N i ( I I ) ^± D d

N i ( I I ) ] o r association w i t h f e r r o m a g n e t i c o r a n t i -

4h

ferromagnetic

23

Complexes

coupling.

Temperature

independent

(Pauli)

paramag-

n e t i s m a r i s i n g f r o m t h e m a g n e t i c m o m e n t o f c o n d u c t i o n electrons u s u a l l y is n o t o b s e r v e d f o r i n o r g a n i c c o m p l e x e s i n t h e s o l i d state b u t is c h a r a c teristic of a m e t a l l i c system (40).

T h u s the molar magnetic susceptibility

should be positive i n sign a n d lower i n value than w o u l d b e expected for one u n p a i r e d e l e c t r o n p e r m e t a l site, i.e. fi

< 1.73 B M . A o n e - d i m e n -

ett

s i o n a l m e t a l l i c system s h o u l d e x h i b i t t e m p e r a t u r e - i n d e p e n d e n t netism.

A

variety

of

first-row

paramagnetic

metal

paramag-

complexes,

e.g.

M e N M n C l , forms c o l u m n a r structures i n t h e s o l i d state w h i c h e x h i b i t 4

3

a n t i f e r r o m a g n e t i c c o u p l i n g (6, 41, 42).

E x a m p l e s of systems w i t h f e r r o -


m a g n e t i c c o u p l i n g h a v e also b e e n r e p o r t e d (6, Electrical

41).

Properties

M o s t inorganic a n d organic materials have l o w conductivity i n either s i n g l e - c r y s t a l or p o l y c r y s t a l l i n e f o r m . ohm^cm"

V a l u e s t y p i c a l l y less t h a n 1 0 "

10

are o b s e r v e d , a n d t h e complexes are l a b e l e d as to i n s u l a t o r s .

1

T h e s e m a t e r i a l s are p r o b a b l y large g a p s e m i c o n d u c t o r s

w i t h large i m -

p u r i t y c o n t r i b u t i o n s , a n d o n l y a c a r e f u l , d e t a i l e d s t u d y of t h e t e m p e r a t u r e d e p e n d e n c e of t h e e l e c t r i c a l c o n d u c t i v i t y

( i n c l u d i n g e l e c t r i c field d e -

p e n d e n c e ) o n single crystals c a n a d e q u a t e l y c h a r a c t e r i z e t h e m . A p l o t of l o g c o n d u c t i v i t y vs. i n v e r s e t e m p e r a t u r e s h o u l d r e s u l t i n a straight l i n e f o r a s e m i c o n d u c t o r ( a s s u m i n g t h a t the m o b i l i t y is t e m p e r a t u r e i n d e p e n d e n t ) . S o m e i n o r g a n i c c o m p l e x e s a t y p i c a l l y h a v e a m u c h l a r g e r c o n d u c t i v i t y at r o o m t e m p e r a t u r e w h i c h m a y arise f r o m a m e t a l l i c state. I n contrast to a s e m i c o n d u c t o r , t h e c o n d u c t i v i t y of a m e t a l increases w i t h d e c r e a s i n g t e m p e r a t u r e a n d exhibits a m o r e c o m p l e x t e m p e r a t u r e d e p e n d e n c e . T h u s a d e t a i l e d s t u d y of t h e t e m p e r a t u r e d e p e n d e n c e is necessary to d i s t i n g u i s h b e t w e e n a s m a l l g a p s e m i c o n d u c t o r a n d a m e t a l l i c state (6).

K Pt(CN) 2

4

Br .3oo • 3 H 0 ( a n d p o s s i b l y t h e c h l o r o a n a l o g u e ) is t h e o n l y 1 - D t r a n s i 0

2

t i o n m e t a l c o m p l e x w h i c h has b e e n c h a r a c t e r i z e d so f a r as a m e t a l A t r o o m t e m p e r a t u r e , K P t ( C N ) B r . 3 o o * 3 H 0 has a c o r r e c t e d 2

4

t i v i t y (43) of ~ 5 . 5 X 1 0 o h r n ^ c m " 3

10" f o r K P t ( C N ) 6

2

4

2

0

1

(7)

(2,6). conduc-

[ c o m p a r e d w i t h v a l u e s of ~ 9 X

• * H 0 ( 44) a n d 9.4 X 1 0 f o r p l a t i n u m m e t a l 2

4

(45)]

a n d a n a n i s o t r o p i c c o n d u c t i v i t y r a t i o (o-||/o-j_) of 1 0 ( 7 ) . I n a d d i t i o n to 5

h i g h c o n d u c t i v i t y , a l o w v a l u e f o r t h e t h e r m o e l e c t r i c p o w e r also c h a r a c terizes a m e t a l l i c state

(6).

Crystallography B y definition, 1-D complexes have a columnar structure. T h e p r o p erties associated w i t h these c o m p l e x e s arise f r o m t h e e l e c t r o n i c a n d steric


24

INORGANIC

properties of the molecules interactions. m e t a l atoms,

UNUSUAL

PROPERTIES

i n the chain a n d the inter- a n d intrachain

F o r 1-D square t h e spacings

COMPOUNDS WITH

planar complexes w h i c h have

characterize

spacings m a y b e equivalent

collinear

the resultant properties.

(Structure I I ) or inequivalent

The

(Structure

III) throughout the chain.

II

III


W i t h e q u i v a l e n t s p a c i n g t h e shorter t h e s p a c i n g s , t h e stronger t h e anisotropic properties.

C o m p l e x e s w h i c h h a v e short e q u i v a l e n t s p a c i n g s ,

i.e. ^ 3.0 A , h a v e b e e n c h a r a c t e r i z e d as p a r t i a l l y o x i d i z e d as t h e y h a v e h i g h e l e c t r i c a l c o n d u c t i v i t y as w e l l as s t r o n g l y a n i s o t r o p i c p r o p e r t i e s , K Pt(CN) Bro.3oo ' 3 H 0 with 2

4

2

~ 2 . 8 8 A spacings

(46)

e.g.

Table I ) .

(see

F o r m o d e r a t e s p a c i n g s , ~ 3 . 0 ~ 3.5 A , t h e o b s e r v e d a n i s o t r o p i c p r o p e r t i e s are n o t as d r a m a t i c a n d l o w c o n d u c t i v i t y is o b s e r v e d , e.g. K P t ( C N ) 2

4

•

x H o O [ ~ 3 . 5 A (49)~\. F o r crystals w i t h spacings w h i c h e x c e e d t h e v a n der W a a l r a d i i , the complexes d o not exhibit enhanced properties. f o r m short spacings a r e n o t sufficient to w a r r a n t e n h a n c e d

Uni-

properties.

S t r o n g m e t a l - m e t a l i n t e r a c t i o n s are i m p o r t a n t . T h u s , square p l a n a r t h i r d r o w t r a n s i t i o n m e t a l c o m p l e x e s w i t h t h e greater s p a t i a l extent a n d i n t e r a c t i o n w i t h n e i g h b o r i n g c o m p l e x e s of t h e 5d 2 o r b i t a l e n h a n c e t h e a n i s o Z

t r o p i c p r o p e r t i e s w i t h respect to t h e first a n d s e c o n d r o w congeners

(4,6).

A v a r i e t y of d i v a l e n t 1 - D i n o r g a n i c c o m p l e x e s a r e c o m p r i s e d o f a l t e r n a t i n g cations a n d anions. T h e most e x t e n s i v e l y s t u d i e d m e m b e r o f t h i s class is M a g n u s ' G r e e n Salt, [ P t ( N H ) ] 3

[ P t C l ] (4, 6).

4

Complexes of

4

this t y p e , as w e l l as c o m p l e x e s c o m p r i s e d o f c h a i n s o f i d e n t i c a l n e u t r a l molecules

(6)

[e.g. P t ( e t h y l e n e d i a m i n e ) C l n

P d , P t ) ] containing metals w i t h

filled

or M ( H D P G )

2

2

( M= Ni,

v a l e n c e shells e x h i b i t

moderate

( ^ 3 . 5 A ) to l o n g ( ^ 3 . 5 A ) spacings, d i c h r o i c o p t i c a l p r o p e r t i e s , d i a m a g netism, a n d l o w conductivity. Several 1-D inorganic complexes are comprised of alternating m i x e d v a l e n t c o m p l e x e s w i t h l o n g e q u i v a l e n t m e t a l - m e t a l spacings. of t h i s t y p e h a v e b e e n o b s e r v e d f o r A u - A u T

(4, 6).

i n

T h e complexes of [ M ( a m i n e ) X ] 2

h a v e h a l i d e atoms b r i d g i n g t h e M

1

1

and M

n

I V

I

V

Complexes

, and P t - P t

( X = halide)

3

associated w i t h t h e t e t r a v a l e n t m e t a l (6).

, Pd -Pd

n

I V

stoichiometry

atoms, b u t t h e y a r e c l e a r l y

T h e resultant properties are

best d e s c r i b e d i n terms o f t h e s u m of t h e i n d i v i d u a l m o l e c u l e s a n d a r e p l a c e d i n C l a s s I I b y R o b i n a n d D a y (21, 24).

L o w c o n d u c t i v i t y has b e e n

o b s e r v e d f o r c o m p o u n d s o f this t y p e .


2.

One-Dimensional

MILLER

25

Complexes

S o m e c o l l i n e a r c o m p l e x e s d o n o t h a v e c o l l i n e a r m e t a l - m e t a l atoms, e.g. P ( C H ) 3 C H 3 N i [ S C ( C N ) ] 6

5

+

2

2

2

2

1

- (Complex I V )

does not h a v e e q u i v a l e n t i n t e r p l a n a r spacings.

(50).

Complex I V

T h i s complex exhibits a

s i n g l e g r o u n d state w i t h a l o w l y i n g t r i p l e t e x c i t e d state (51). cal properties characterize C o m p l e x

Its e l e c t r i -

I V as a n i n t r i n s i c s e m i c o n d u c t o r

a l o n g the c h a i n axis w i t h a n a n i s o t r o p i c c o n d u c t i v i t y

(35).

Structures of 1-D a n t i f e r r o m a g n e t i c a l l y c o u p l e d p a r a m a g n e t i c r o w t r a n s i t i o n metals e x h i b i t l i g a n d b r i d g e d p o l y m e r s w i t h l o n g m e t a l - m e t a l spacings (6, 41, 42).

F o r example, N M e M n C l 4

c h a i n w i t h t h r e e b r i d g i n g h a l i d e atoms b e t w e e n t h e d

5

Mn

first

equivalent has a

3

atoms t h a t

1 1

p r o v i d e s a p a t h w a y for m a g n e t i c c o u p l i n g .


I n s u m m a r y , c r y s t a l s t r u c t u r e d i r e c t l y relates t o t h e t y p e a n d extent of i n t e r m o l e c u l a r interactions w h i c h c h a r a c t e r i z e t h e p r o p e r t i e s of system.

the

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

w i t h short e q u i v a l e n t spacings e x h i b i t the strongest a n i s o t r o p i c p r o p e r t i e s . T h e s e 1-D crystals a r e d a r k , d i c h r o i c needles w h i c h m a y a p p e a r m e t a l l i c . C h a i n c o m p l e x e s of the first r o w p a r a m a g n e t i c ions f r e q u e n t l y e x h i b i t 1-D antiferromagnetic coupling. Stoichiometry A n i m p o r t a n t a r t i f a c t of h i g h l y c o n d u c t i n g 1-D m a t e r i a l s is the p a r t i a l l y o x i d i z e d c h a r a c t e r of t h e m e t a l w h i c h results f r o m n o n s t o i c h i o m e t r y of ions i n the u n i t c e l l ( T a b l e I ) . F o r e x a m p l e , K P t ( C N ) B r . 3 o o • 3 H 0 2

4

m a y b e m a d e r e p r o d u c i b l y w i t h a 0.300:1: : B r : P t (11)

2

0

r a t i o : thus t h e sys-

t e m is n o n s t o i c h i o m e t r i c . H i s t o r i c a l l y this was e x p l a i n e d b y t h e i n v o c a t i o n of m i x e d v a l e n c e states for t h e m e t a l . R e c e n t w o r k has r e v e a l e d u n e q u i v o c a l l y that a l l the m e t a l atoms are e q u i v a l e n t (1, 2, 3, 4,5,6) classified b y R o b i n a n d D a y as C l a s s I I I - B (21,

24).

a n d they are

The unusual con-

d u c t i v i t y of these systems arises d i r e c t l y f r o m the e l e c t r o n i c associated w i t h the p a r t i a l l y o x i d i z e d ( n o n s t o i c h i o m e t r i c ) Nonstoichiometry

can be

assessed b y

precise

properties

system.

e l e m e n t a l analysis.

E x t r e m e care m u s t b e t a k e n to ensure that r e p r o d u c i b l e n o n s t o i c h i o m e t r y is c h a r a c t e r i z e d .

F o r example,

absorption spectra, x-ray

fluorescence,

n e u t r o n a c t i v a t i o n , a n d mass s p e c t r a l analysis w e r e u s e d to d e t e r m i n e t h e 0.300 ±

0 . 0 0 6 : 1 : : B r : P t r a t i o for K P t ( C N ) B r . o o • 3 H 0 2

4

0

3

2

(10).

The

errors associated w i t h r o u t i n e e l e m e n t a l analysis a l l o w significant differences i n the s t o i c h i o m e t r y of n o n s t o i c h i o m e t r i c m a t e r i a l s .

I n order

to

u n d e r s t a n d f u l l y the p h y s i c s of 1-D systems, it is i m p e r a t i v e that the exact s t o i c h i o m e t r y be k n o w n as this relates d i r e c t l y t o the b a n d

filling

which,

i n g e n e r a l , cannot b e o b t a i n e d b y a l t e r n a t i v e t e c h n i q u e s . A p a i r of c o m p u t e r p r o g r a m s w a s w r i t t e n to a i d i n t h e i n t e r p r e t a t i o n of c h e m i c a l analysis (52,

53).

F o r e x a m p l e , o x i d a t i o n of b i s ( d i p h e n y l -


26

INORGANIC

COMPOUNDS WITH

Table I. Complex

M-M,

(Cation) P t ( C N ) X ^ . i • 2 / H 0 2

4

0

K . Pt(CN)4-2/H 0 (Cation) J?t(0rf3t0*),-»Hrf) 1

7 4

I r ( C O ) i C l i . or I r ( C O ) C l i . (Cation) J r (CO) X w

3

2

C ations/A

A

~2.95 2.88-2.9

2

M

Classes of H i g h l y Conducting

2.88-2.95

2

2


2

2

4

6

6

x

3

2 +

H + , K + , Cs+, N M e + 4 , AsPh+4, L i + Mg +, B a C1-, (Br-?, I-?)

2.8-3.0 2.64 1°

0.5 ?


0.5 >10« 8 X 10 >10 >10 >

3c

3 a

0

Ze

d

* From Ref. 48. Anisotropy is suggested by crystallographic data, but it has not been confirmed experimentally. A superconducting transition has been observed at ~ 0 . 3 ° K , Ref. 61. 1

9

glyoximato)nickel(II),

N i ( H D P G ) , w i t h h a l o g e n (54, 55, 56) y i e l d s a 2

series o f m a t e r i a l s of M ( H D P G ) X y ( X = B r , I ; 0 < y < 1.15) s t o i c h i 2

o m e t r y i n contrast to p r e v i o u s l i t e r a t u r e reports.

A preliminary report

suggests s i m i l a r p r o p e r t i e s f o r 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 o ) c o m p l e x e s of t h e n i c k e l t r i a d (57). F i g u r e 2 depicts a s a m p l e c o m p u t e r o u t p u t w h i c h characterizes a set o f analysis as N i ( H D P G ) B r . 7 9 - o . 8 2 . 2

crystallography Ni(HDPG)

2

demonstrated

0

Microscopy a n d

t h a t this m a t e r i a l is n o t a m i x t u r e o f

a n d N i ( H D P G ) B r as is suggested b y t h e d a t a t h a t a p 2

p e a r e d p r e v i o u s l y i n t h e l i t e r a t u r e (58). A n e w material m a y or m a y not be nonstoichiometric. plexes a r e s t o i c h i o m e t r i c .

Most com-

I f a n i n o r g a n i c c o m p l e x e x h i b i t s h i g h aniso-

tropic conductivity, the complex m a y be nonstoichiometric. U p o n r e v i e w i n g the properties of inorganic complexes w h i c h exhibit h i g h c o n d u c t i v i t y , o n e notices s e v e r a l trends w h i c h m a y b e i n s t r u c t i v e i n the p r e d i c t i o n o f n e w m a t e r i a l s . T h e i n o r g a n i c 1 - D m a t e r i a l s t h a t a r e characterized b y h i g h conductivity (Table I ) are comprised of partially o x i d i z e d square p l a n a r I r a n d P t c o m p l e x e s w h i c h c o n t a i n r i g o r o u s l y 1

planar ligands. spacings

n

T h e o v e r a l l g e o m e t r y a l l o w s f o r short

a n d strong intermolecular interactions

intermolecular

(provided

for b y the

greater s p a t i a l extent o f t h e 5dz* o r b i t a l w i t h respect t o t h e 4d * a n d z

3(2*2 o r b i t a l s ) . P a r t i a l o x i d a t i o n seems to b e necessary f o r h i g h c o n d u c t i v i t y a n d seems t o r e q u i r e a p a i r o f stable o x i d a t i o n states, b u t p a r t i a l o x i d a t i o n m a y s t a b i l i z e a p r e v i o u s l y u n c h a r a c t e r i z e d o x i d a t i o n state o f a


28

INORGANIC

COMPOUNDS

m e t a l . T o date n o p a r t i a l l y o x i d i z e d A u

m

WITH

UNUSUAL PROPERTIES

complexes h a v e b e e n r e p o r t e d .

T h i s m a y b e a t t r i b u t a b l e to t h e i n s t a b i l i t y of A u

I V

o r to t h e h i g h e r c h a r g e

w h i c h w i l l decrease t h e s p a t i a l extent of t h e 5d * o r b i t a l . T h e l i g a n d s z

(1,4,6)

w h i c h h a v e b e e n successful i n s t a b i l i z i n g p a r t i a l l y o x i d i z e d m a t e -

rials r a n g e f r o m m o n o d e n t a t e

( C O , C I , C N ) to b i d e n t a t e ( o x a l a t e ) a n d

f r o m a strong field l i g a n d ( C O ) t o a w e a k field l i g a n d ( o x a l a t e ) .

Thus no

c o n c l u s i o n c a n b e m a d e a b o u t t h e l i g a n d s except f o r t h e i r p l a n a r i t y . C o m p l e x e s c o n t a i n i n g m a c r o c y l i c l i g a n d s are p o o r c a n d i d a t e s f o r f o r m i n g a h i g h l y c o n d u c t i n g 1 - D m a t e r i a l s as t h e v a n d e r W a a l r a d i i f o r t h e i n t e r m o l e c u l a r ir i n t e r a c t i o n s (i.e. > 3.3 A ) is greater t h a n t h e spacings r e q u i r e d f o r strong m e t a l - m e t a l o v e r l a p (i.e. < 3.0 A ) .

C a t i o n i c square


p l a n a r complexes a r e also p o o r c a n d i d a t e s f o r t h e f o r m a t i o n of a h i g h l y conducting

complex

as t h e p l u s c h a r g e w i l l c o n t r a c t t h e 5d * o r b i t a l z

d i m i n i s h i n g the o v e r l a p b e t w e e n adjacent molecules i n the c h a i n . T h u s a l i k e l y c a n d i d a t e f o r t h e f o r m a t i o n of a n e w h i g h l y c o n d u c t i n g m a t e r i a l w o u l d b e b a s e d o n I r ( C N ) ~ . T h e 3 — c h a r g e o n this d c o m p l e x s h o u l d I

4

3

8

increase t h e s p a t i a l extension of t h e 5d * o r b i t a l e n a b l i n g stronger i n t e r z

m o l e c u l a r o v e r l a p a l o n g the c h a i n . I n i t i a l attempts a t p r e p a r i n g I r ( C N ) has l e d to t h e i s o l a t i o n of I r

n i

4

3

~

( C N ) H ~ f r o m a l c o h o l a n d w a t e r solutions 5

3

(1, 59) a l t h o u g h the R h a n a l o g has r e c e n t l y b e e n i s o l a t e d as t h e salt of a 1

b u l k y c a t i o n (60). N e w m a t e r i a l s are necessary to c h a r a c t e r i z e the i n o r g a n i c p a r a m e t e r s associated w i t h t h e h i g h l y c o n d u c t i n g materials as w e l l as to u n d e r s t a n d the physics of one dimension

(2,3,5,6).

Literature Cited 1. Krogmann, K., Angew. Chem. Int. Ed. Engl (1969) 8, 35. 2. Zeller, H . R., Advan. Solid State Phys. (1973) 13, 31. 3. Shchegolev, I. F., Phys. Status Solidi A (1972) 12, 9. 4. Thomas, T. W., Underhill, A. E., Chem. Soc. Rev. (1972) 1, 99. 5. Garito, A. F., Heeger, A. J., Acc. Chem. Res. (1974) 7, 232. 6. Miller, J. S., Epstein, A. J., Prog. Inorg. Chem. (1975) 20, 1 and references therein. 7. Zeller, H. R., Beck, A., J. Phys. Chem. Solids (1974) 35, 77. 8. Bernasconi, J., Bruesch, P., Kuse, D., Zeller, H . R., J. Phys. Chem. Solids (1974) 35, 145. 9. Geserich, H . P., Hausen, H . D., Krogmann, K., Stampel, P., Phys. Status Solidi A (1972) 9, 187. 10. Saillant, R. B., Jaklevic, R. C., ACS Symp. Ser. (1974) 5, 376. 11. Saillant, R. B., Jaklevic, R. C., Bedford, C. D., Mater. Res. Bull. (1974) 9, 289. 12. Malatesta, L., Canziani, F., J. Inorg. Nucl. Chem. (1961) 19, 81. 13. Cleare, M . J., Griffith, W. P., J. Chem. Soc. A (1970) 2788. 14. Churchill, M . R., Bau, R., Inorg. Chem. (1968) 7, 2606. 15. Buravov, L . N., Stepanova, K. N., Khidekel', M . L., Shchegolev, I. F., Dokl. Chem. (1972) 203, 283.



2.

MILLER

One-Dimensional

Complexes

29

16. Krogmann, K., Geserich, H . P., Wagner, H., Zielke, H . J., "Abstracts of Papers," 167th National Meeting, ACS, March 1974, INOR 221. 17. Shupack, S. I., Billig, E., Clark, R. J. H., Williams, R., Gray, H . B.,J.Amer. Chem. Soc. (1964) 86, 4594. 18. Maki, A. H., Edelstein, N., Davison, A., Holm, R. H., J. Amer. Chem. Soc. (1964) 86, 4586. 19. Allen, G. C., Hush, N. S., Prog. Inorg. Chem. (1967) 8, 357. 20. Hush, N. S., Prog. Inorg. Chem. (1967) 8, 391. 21. Robin, M . B., Day, P., Adv. Inorg. Chem. Radiochem. (1967) 10, 247. 22. Cowan, D. O., LeVanda, C., Park, J., Kaufman, F., Acc. Chem. Res. (1973) 6, 1. 23. Day, P., ACS Symp. Ser. (1974) 5, 234. 24. Day, P., NATO Adv. Study Inst. (1975) 7B, 191. 25. Creutz, C., Taube, H., J. Amer. Chem. Soc. (1969) 91, 3988. 26. Ibid. (1973) 95, 1086. 27. Liptay, W., Angew. Chem. Int. Ed. Engl. (1969) 8, 177. 28. Reichardt, C., Angew. Chem. Int. Ed. Engl. (1965) 4, 29. 29. Dance, I. G., Miller, T. R., J. Chem. Soc. Chem. Commun. (1973) 433. 30. Miller, J., Balch, A. L., Inorg. Chem. (1971) 10, 1410. 31. Bernal, I., Clearfield, A., Epstein, E. F., Ricci, J. S., Jr., Balch, A., Miller, J. S., J. Chem. Soc. Chem. Commun. (1973) 39. 32. Banks, C. V., Barnum, D. W., J. Amer. Chem. Soc. (1958) 80, 3579. 33. Ibid. (1958) 80, 4767. 34. Miller, J. S., Goldberg, S. Z., accepted for publication. 35. Miller, J. S., Epstein, A. J., "Abstracts of Papers," 167th National Meeting, ACS, March 1974, INOR 110. 36. Watt, G. W., McCarley, R. E., J. Amer. Chem. Soc. (1957) 79, 4585. 37. Dessent, T. A., Palmer, R. A., Horner, S. M . , ACS Symp. Ser. (1974) 5, 301. 38. Pitt, C. G., Monteith, L. K., Ballard, L . F., Collman, J. P., Morrow, J. C., Roper, W. R., Ulkü, D., J. Amer. Chem. Soc. (1966) 88, 4286. 39. Cervantes, M . , "Don Quixote," Part II, Book III, Chap. 33, p. 1615. 40. Kittel, C., "Introduction to Solid State Physics," 4th ed., p. 518, John Wiley & Sons, New York, 1971. 41. Ackerman, J. F., Cole, G. M., Holt, S. L., Inorg. Chim. Acta (1974) 8, 323. 42. Hone, D. W., Richards, P. M . , Ann. Rev. Mater. Sci. (1974) 4, 337. 43. Miller, J. S., J. Amer. Chem. Soc. (1974) 96, 7131. 44. Minot, M . J., Perlstein, J. H., Phys. Rev. Lett. (1971) 26, 371. 45. "Handbook of Chemistry and Physics," 53rd ed., p. F145, Chemical Rubber, Cleveland, 1972. 46. Krogmann, K., Hausen, H . D., Z. Anorg. Allg. Chem. (1968) 358, 67. 47. Cutforth, B. D., Datars, W. R., Gillespie, R. J., van Schyndel, A., ADVAN. C H E M . SER. (1975) 150, 56.

48. MacDiarmid, A. G., MiKulski, C. M . , Saran, M . S., Russo, P. J., Cohen, M. J., Bright, A. F., Garito, A. J., Heeger, A. J., ADVAN. C H E M . SER.

(1975) 150, 63. 49. Moreau-Colin, M . L., Bull. Soc. R. Sci. Liege (1965) 34, 778. 50. Fritchie, C. J., Jr., Acta Crystallogr. (1966) 20, 107. 51. Weiher, J. F., Melby, L. R., Benson, R. E., J. Amer. Chem. Soc. (1964) 86, 4329. 52. Miller, J. S., Goedde, A. O., J. Chem. Educ. (1973) 50, 431. 53. Miller, J. S., Kirschner, S. Kravitz, S. H , Ostrowski, P., manuscript in preparation. 54. Edelman, L. E., J. Amer. Chem. Soc. (1950) 72, 5765. 55. Foust, A. S., Soderberg, R. H., J. Amer. Chem. Soc. (1967) 89, 5507. 56. Keller, H . J., Seibold, K., J. Amer. Chem. Soc. (1971) 93, 1309.


30

INORGANIC

COMPOUNDS

WITH UNUSUAL

PROPERTIES

57. Endres, H . , Keller, H . J . , Mégnamisi-Bélombé, Moroni, W., Nörte, D., Inorg. Nucl. Chem. Lett. (1974) 10, 467. 58. Miller, J. S., Griffiths, C. H., manuscript in preparation. 59. Krogmann, K., Binder, W., Angew. Chem., Int. Ed. Engl. (1967) 6, 881. 60. Halpern, J., Cozens, R., Goh, L-Y., Inorg. Chim. Acta. (1975) 12, L35. 61. Greene, R. L., Street, G. B., Suter, L. J., Phys. Rev. Lett. (1975) 34, 577.


RECEIVED January 24, 1975.


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