Metal Tetrathiolenes: Chemistry, Stereochemistry ... - ACS Publications

29 Metal Tetrathiolenes: Chemistry, Stereochemistry, Electrochemistry, and Semiconductivity

Downloaded by CORNELL UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch029

BOON-KENG TEO B e l l Telephone Laboratories, M u r r a y Hill, N J 07974

A class of organochalcogen two chalcogen-chalcogen

compounds containing one or

bonds was chosen as ligands for

organometallic synthesis. New discrete molecular complexes containing two, four, and six metal atoms were

prepared

and characterized. These cluster systems exhibit rich electro chemistry as established by cyclic voltammetry and unusual stereochemistry as revealed by x-ray crystallography. A new class of organometallic polymers based on these ligands was synthesized

and

characterized.

Temperature-dependent

electrical conductivity measurements revealed

semiconduc

tivity consistent with pseudo-one-dimensionality.

Electrical

conductivity can be correlated with the oxidation potential of the free ligands.

These new semiconducting

organo

metallic polymers can be used as reversible anode materials for a rechargeable battery system.

" O e c e n t l y there has b e e n c o n s i d e r a b l e interest i n t h e m o l e c u l a r d e s i g n of b i m e t a l l i c c o m p l e x e s b r i d g e d b y a q u a d r i d e n t a t e o r a b i s - b i d e n tate l i g a n d w i t h h i g h l y d e l o c a l i z e d TT system (1-28).

O n e incentive for

s u c h a n a t t e m p t is to synthesize n e w b i m e t a l l i c clusters that a r e p o t e n t i a l l y c a p a b l e of f o r m i n g m u l t i p a r a l l e l stacks of p s e u d o - o n e - d i m e n s i o n a l systems v i a i n t e r m o l e c u l a r m e t a l a n d / o r l i g a n d o r b i t a l o v e r l a p s 7_9,

(1—5,

24-28). W e h a v e c h o s e n a class of o r g a n o c h a l c o g e n c o m p o u n d s c o n t a i n i n g

one o r t w o c h a l c o g e n - c h a l c o g e n b o n d s as p o t e n t i a l l i g a n d s f o r o r g a n o m e t a l l i c synthesis (1,2,3,4,5).

T y p i c a l members are C i H X Y 0

6

0-8412-0429-2 / 79 / 33-173-364$05.75/ 0 © 1979 American Chemical Society King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

(where

29.

TEO

Metal

365

Tetrathiolenes

X

Y

Figure 1. Dichalcolene ligands involving 1,8-substituted naphthalene systems

X Y = S S , SeSe,TeTe


SSe,STe,SeTe XY = one C

1 8

S , S e , T e , SSe, S T e , a n d S e T e ) (29,30,31,32) 2

2

H X 8

bond

(34,35), a n d C C 1 X

4

w h i c h contain

2

chalcogen-chalcogen 1 0

4

(cf. F i g u r e

1)

and Ci H X 0

4

4

(33),

(36) w h e r e X = S, Se, a n d T e ) w h i c h

4

contain t w o chalcogen-chalcogen bonds (cf. F i g u r e 2 ) . These organic m o l e c u l e s possess three f a v o r a b l e steric a n d e l e c t r o n i c features m a k e t h e m excellent l i g a n d s . extensive

electron

derealization

chalcogen bond(s)

which

First, they are structurally planar w i t h (29-36).

- Secondly,

the chalcogen-

i n e a c h of these m o l e c u l e s are w e l l s u i t e d f o r o x i -

d a t i v e a d d i t i o n reactions w i t h l o w - v a l e n t t r a n s i t i o n m e t a l c o m p l e x e s 2,3,4,5).

(1,

F o r t h e latter class of t e t r a c h a l c o g e n l i g a n d s , i t m a y constitute

a b r i d g e b e t w e e n t w o m e t a l atoms (1,2, 3, 4,5).

Finally, upon coordina-

t i o n t o o n e o r t w o m e t a l atoms, t h e d i - a n d t e t r a c h a l c o g e n l i g a n d s c a n a c c o m m o d a t e a f o r m a l c h a r g e of —2 a n d —4, r e s p e c t i v e l y (1,4).

The

i m p l i c a t i o n of s u c h a q u a l i t a t i v e c o n s i d e r a t i o n is that t h e r e s u l t i n g c o m plexes, w h i c h c a n a p p r o p r i a t e l y b e t e r m e d as m e t a l d i - a n d t e t r a c h a l c o lenes, w i l l e x h i b i t u n u s u a l l y r i c h e l e c t r o c h e m i s t r y (4).

I n this c h a p t e r ,

w e w i l l first g i v e a g e n e r a l v i e w o n t h e l i g a n d s a n d t h e n restrict ourselves to t h e m e t a l tetrathiolenes i n t h e s u b s e q u e n t discussions. Conceivably,

m e t a l tetrachalcolenes

of t h e types

exemplified i n

F i g u r e 3 f o r m e t a l tetrathiolenes c a n b e s y n t h e s i z e d . F o r discrete p o l y n u c l e a r m e t a l c o m p l e x e s , o n e c a n either b u i l d u p t h e o l i g o m e r i c clusters by f o r m i n g in-plane, m e t a l - l i g a n d a bonds w i t h tetrathiolene a n d other S—: S

S—S

S—S

S—S

S—S

S—S

TTT

TTN

TCTTN

Figure 2. Tetrathiolene ligands (a subclass of tetrachalcolenes) C H S,(TTT), C HtSJTTN), and C Cl S (TCTTN) 18

8

10

10

fy

h

King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

366

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES


MOLECULAR CLUSTERS

ORGANOMETALLIC POLYMERS

(b) Figure 3.

II

(d)

Examples of molecular and polymeric metal tetrathiolenes, subclass of metal tetrachalcolenes

a

b i d e n t a t e l i g a n d s ( F i g u r e 3 a ) o r f o r m s m a l l clusters b y o u t - o f - p l a n e 7r-orbital o v e r l a p s ( F i g u r e 3 b ) . F o r t h e p o l y m e r i c species, o n e c a n h a v e p s e u d o - o n e - d i m e n s i o n a l c h a i n s w i t h a l t e r n a t i n g units of m e t a l atoms ( o r c o m p l e x e s ) a n d t h e tetrathiolene l i g a n d s ( F i g u r e 3 c ) or m u l t i p l e c o l u m n a r stacks of m e t a l c o m p l e x e s a n d / o r t h e l i g a n d s ( F i g u r e 3 d ) . I t is o b v i o u s t h a t F i g u r e s 3c a n d 3 d c a n f o r m a l l y b e c o n s i d e r e d as extensions of F i g u r e s 3 a a n d 3 b . A f u r t h e r v a r i a t i o n of F i g u r e s 3 b a n d 3 d m a y i n v o l v e t h e c o r r e s p o n d i n g " s t a g g e r e d " structures, w i t h t h e m e t a l atoms i n t e r a c t i n g w i t h t h e sulfurs rather t h a n t h e metals of t h e a d j a c e n t u n i t ( s ) or c h a i n ( s )

( 3 7 ) . I t is also r e a d i l y a p p a r e n t that f o r s t r u c t u r a l types

s h o w n i n F i g u r e s 3 b a n d 3 d , i t is necessary t o m i n i m i z e t h e steric r e q u i r e ments of t h e t e r m i n a l l i g a n d s . A s u m m a r y of o u r recent attempts i n t h e synthesis, c h a r a c t e r i z a t i o n , structure, a n d b o n d i n g of n e w m e t a l t e t r a t h i o l e n e clusters a n d p o l y m e r s w i l l b e p r e s e n t e d . E m p h a s i s w i l l b e p l a c e d o n t h e i r n o v e l stereochemistry, t h e i r u n u s u a l l y r i c h e l e c t r o c h e m i s t r y , a n d t h e i r i n t e r e s t i n g p h y s i c a l p r o p e r t i e s (1,2,3,4,5),

w i t h t h e h o p e of g e n e r a t i n g a n d u n d e r s t a n d i n g

n e w m a t e r i a l s of t e c h n o l o g i c a l significance. Organocbalcogen

Ligands

A m a j o r i n c e n t i v e f o r t h e o r g a n i c synthesis of t h e l i g a n d s t o b e d i s c u s s e d i n this section comes f r o m t h e recent intense interest i n p s e u d o o n e - d i m e n s i o n a l " o r g a n i c m e t a l " (31, 33, 38-47). I n fact, 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 of t h e tetrathiotetracene ( T T T ) a n d its m o n o c a t i o n , first s y n t h e s i z e d b y M a r s c h a l k i n 1948 (34,35), has b e e n n o t e d f o r a l o n g


TEO

29. time.

Metal

367

Tetrathiolenes

I t is n o t u n t i l r e c e n t l y that its close analogs,

naphthalene

(TCTTN)

(36)

tetrachlorotetrathio-

a n d tetrathionaphthalene

w e r e m a d e i n 1972 a n d 1976, r e s p e c t i v e l y .

( T T N ) (33),

Similarly, while dithionaph-

t h a l e n e ( D T N ) ( 2 9 ) w a s m a d e i n 1911, t h e seleno a n d t e l l u r o ( a s w e l l as t h e m i x e d c o m b i n a t i o n s ) analogs w e r e r e p o r t e d o n l y r e c e n t l y ( 1 9 7 7 ) (31,32). T o get a n i d e a w h y these d i - o r t e t r a m e r c a p t o c o m p o u n d s are p r o n e to o x i d a t i o n a n d f o r m stable r a d i c a l m o n o c a t i o n s o r d i c a t i o n s , w e n e e d o n l y c o n s i d e r t h e c o n v e r s i o n of n a p h t h a l e n e lene

(DTN, C

1 0


three m o l e c u l e s

H S ) 6

2

( C i H ) to dithionaphtha0

to tetrathionaphthalene

8

(TTN,Ci H S ). All 0

4

are strictly planar w i t h h i g h l y delocalized

4

?r-systems.

H o w e v e r , t h e o r b i t a l characters of t h e h i g h e s t - o c c u p i e d m o l e c u l a r o r b i t a l s ( H O M O ) i n these m o l e c u l e s c h a n g e d r a m a t i c a l l y u p o n r e p l a c e m e n t of the h y d r o g e n s at 1,8 a n d 4,5 p o s i t i o n s , successively, b y t h e s u l f u r atoms. It goes f r o m a n a p h t h y l - r i n g - c e n t e r e d b o n d i n g TT o r b i t a l i n C i H 0

8

to a

d i t h i o - c e n t e r e d TT o r b i t a l w h i c h is a n t i b o n d i n g b e t w e e n t h e t w o s u l f u r atoms i n C i H S 0

6

2

to a tetrathio-centered

TT o r b i t a l w h i c h is a n t i b o n d i n g

b e t w e e n t h e t w o pairs of s u l f u r atoms i n C i H S , as p o r t r a y e d i n F i g u r e s 0

4a, 4 b , a n d 4c, r e s p e c t i v e l y .

4

4

A s e x p e c t e d , w i t h t h e i n c r e a s i n g degree of

a n t i b o n d i n g , t h e o r b i t a l energies rise d r a s t i c a l l y i n t h e same d i r e c t i o n : -12.79, -8.53, and - 6 . 1 7 eV in C

1 0

H , C 8

1 0

H S , and C 6

2

1 0

H S , 4

4

respec-

t i v e l y . T h e s e results w e r e b a s e d o n n o n p a r a m e t e r i z e d m o l e c u l a r o r b i t a l calculations performed using a n approximate

Hartree-Fock-Roothaan

S C F - L C A O m e t h o d d e v e l o p e d b y F e n s k e et a l . (48).

T h i s energetic

t r e n d t h e n p r e d i c t s that i t s h o u l d b e c o m e i n c r e a s i n g l y easy t o o x i d i z e t h e series d o H s - n S ^ w i t h i n c r e a s i n g n = 0,2,4 as d e p i c t e d i n F i g u r e 5 ( t h e potentials are c o n v e r t e d to v s . A g / O . O I M A g N 0 p l a t i n u m e l e c t r o d e ) (30,33).

3

i n acetonitrile

at a

I n fact, i t is p o s s i b l e t o p l o t t h e o r b i t a l

e n e r g y as a f u n c t i o n of t h e o n e - e l e c t r o n o x i d a t i o n p o t e n t i a l f o r t h e c o n -

Figure 4. Representations of highest occupied molecular orbital (HOMO) of naphthalene (a), dithionaphthalene (b), and tetrathionaphthalene (c). The shaded and empty circles represent the positive and negative lobes of the atomic iz orbitals (perpendicular to the molecular plane).


COMPOUNDS


INORGANIC

—

WITH

UNUSUAL PROPERTIES

if)

00

"d LU

fe Q_

®

o

Cvi


]

29.

Metal

TEO

369

Tetrathiolenes

v e r s i o n of t h e n e u t r a l C i H _ S „ t o its r a d i c a l cations [ C i H _ S ] 0

8

w

0

8

M

+

w

as

s h o w n i n F i g u r e 6. A g r a t i f y i n g l i n e a r r e l a t i o n s h i p is c l e a r l y o b s e r v e d . F u r t h e r m o r e , t h e f a c t that t h e e l e c t r o n ( s )

c o m e o u t of o r b i t a l s w h i c h

are h i g h l y a n t i b o n d i n g b e t w e e n t h e s u l f u r atoms f o r n = 2 a n d n = 4 i n Ci H . S 0

8

n

w

suggests t h a t t h e r e s u l t i n g cations s h o u l d b e q u i t e stable.

A n o b v i o u s v a r i a t i o n of these p r o t o t y p e s of o r g a n i c m o l e c u l e s is t h e r e p l a c e m e n t of o n e or b o t h of t h e s u l f u r atoms b y s e l e n i u m o r t e l l u r i u m . T h i s has b e e n d o n e w i t h C i H S . 0

6

I n fact, t h e c o m p l e t e series of c o m -

2

pounds w i t h the general f o r m u l a C i H X Y where X Y = 0

SS, SeSe, T e T e ,

6


SSe, S T e , a n d S e T e r e c e n t l y has b e e n s u c c e s s f u l l y s y n t h e s i z e d a n d c h a r a c t e r i z e d . T h e o x i d a t i o n p o t e n t i a l is b e l i e v e d t o decrease a l o n g t h e series Ci H S , 0

6

CioH Se , and CioH Te .

2

6

2

6

T h e room-temperature-compressed

2

p e l l e t e l e c t r i c a l r e s i s t i v i t y of t h e c o r r e s p o n d i n g m o n o c a t i o n s as T C N Q " salts also decreases d r a m a t i c a l l y f r o m 7.2 X 1 0 a l o n g t h e same series (30,31). e l e c t r i c a l r e s i s t i v i t y (R) a

t o 1 X 1 0 t o 50 o h m - c m 7

T h e t e m p e r a t u r e (T)

d e p e n d e n c e of t h e

f o l l o w the linear relationship InR vs. T "

r e a s o n a b l y l a r g e t e m p e r a t u r e range,

sionality.

1 1

1 / 2

over

suggesting pseudo-one-dimen-

S i m i l a r r e p l a c e m e n t of t h e s u l f u r atoms i n C10H4S4 b y its

h e a v i e r congeners t o f o r m C i o H X Y _ 4

n

4

n

(where X , Y =

0 < n < 4 ) or C H X j Y Z „ ( w h e r e X , Y , Z = 1 0

0.2

4

m

S, Se, o r T e a n d

S, Se, o r T e a n d I + m

0.4 0.6 0.8 1.0 1.2 OXIDATION POTENTIAL (VOLTS) (vs Ag/0.01M Ag N0 )

14

3

Figure 6. A linear correlation of the first one-electron oxidation potential of naphthalene (C H ), dithionaphthalene (C H S ), and tetrathionaphthalene (C^HfiJ with the calculated HOMO energies 10

8

10

6

2


+

370 n =

INORGANIC COMPOUNDS W I T H UNUSUAL

PROPERTIES

II

4 ) has not b e e n r e a l i z e d . S u c h a series of c l o s e l y r e l a t e d c o m p o u n d s

u n d o u b t e d l y w i l l g i v e rise to h i g h l y i n t e r e s t i n g trends of r e d o x p o t e n t i a l s , e l e c t r i c a l c o n d u c t i v i t i e s , as w e l l as other p h y s i c a l or t r a n s p o r t p r o p e r t i e s w h i c h w i l l s h e d l i g h t o n the c h e m i c a l b o n d i n g a n d solid-state p r o p e r t i e s ( e . g . c o l u m n a r s t a c k i n g interactions v i a o r b i t a l o v e r l a p s ) of these species. A

different v a r i a t i o n of these p l a n a r

organic

molecules

can

be

a c h i e v e d b y r i n g s u b s t i t u t i o n . F o r e x a m p l e , f o r m a l r e p l a c e m e n t s of the four hydrogens i n C i H S 0

yield C


2).

1 8

H S 8

4

4

(TTT)

4

( T T N ) b y t w o b e n z o r i n g s a n d f o u r chlorines

and C C 1 S 1 0

4

4

( T C T T N ) , r e s p e c t i v e l y (cf.

T h e s e c o m p o u n d s , h o w e v e r , w e r e m a d e b y different

Figure

procedures

u n d e r different c o n d i t i o n s . T h e r e d o x potentials are also d r a s t i c a l l y d i f ferent.

E a c h m o l e c u l e exhibits t w o r e v e r s i b l e o x i d a t i o n s a n d one

t w o ) irreversible reduction reaction(s).

(or

T h e first o x i d a t i o n step occurs

at —0.05, + 0 . 2 7 , a n d + 0 . 6 4 V w h e r e a s the s e c o n d o x i d a t i o n r e a c t i o n occurs at + 0 . 4 4 , + 0 . 6 5 , a n d + 0 . 9 7 V f o r T T T TCTTN

(4),

T T N (33),

and

i n F i g u r e 7.

The

(49),

r e s p e c t i v e l y , as s h o w n s c h e m a t i c a l l y

c o r r e s p o n d i n g i r r e v e r s i b l e r e d u c t i o n w a v e occurs at —1.30 ( a l s o —1.67), — 1.42,

a n d —1.26 V .

Ag/O.OIM A g N 0 . 3

0.07 to -

T h e s e values are s t a n d a r d i z e d w i t h respect

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 of the m o n o c a t i o n s

1 a n d 40 ( o h m - c m ) "

1

for T T T

(38,39,40)

and T T N

to are

(33),

+

r e s p e c t i v e l y . It is clear that there seems to b e a c o r r e l a t i o n b e t w e e n the e l e c t r i c a l c o n d u c t i v i t y a n d the o x i d a t i o n p o t e n t i a l : v i z , as the ease of o x i d a t i o n declines a l o n g the series T T T , T T N , T C T T N , so does the c o n ductivity.

T h i s m a y b e r e l a t e d to the b a n d g a p of the

semiconducting

m o n o c a t i o n i c species w h i c h , q u a l i t a t i v e l y s p e a k i n g , increases w i t h

the

l o w e r i n g of the e n e r g y of the h i g h e s t o c c u p i e d m o l e c u l a r o r b i t a l w h i c h , i n t u r n , correlates w i t h the d e c l i n e of the ease of o x i d a t i o n . It occurs to us that these p l a n a r , h i g h l y 7r-delocalized, easily r e d o x e d o r g a n o c h a l c o g e n c o m p o u n d s c a n f u n c t i o n as excellent l i g a n d s i n o r g a n o m e t a l l i c synthesis. T h e c h a l c o g e n - c h a l c o g e n b o n d ( s ) i n these m o l e c u l e s c a n u n d e r g o f a c i l e o x i d a t i v e - a d d i t i o n reactions w i t h a v a r i e t y of i n o r g a n i c or o r g a n o m e t a l l i c c o m p o u n d s , e s p e c i a l l y those w i t h l o w o x i d a t i o n states, t h e r e b y p r o d u c i n g o l i g o m e r i c or p o l y m e r i c o r g a n o m e t a l l i c plexes c o m p r i s e d of chains of t r a n s i t i o n metals b r i d g e d b y the

comabove-

m e n t i o n e d t e t r a c h a l c o g e n l i g a n d s as w e l l as other b i d e n t a t e l i g a n d s . free ends of these clusters or chains c a n b e t e r m i n a t e d b y the

The

above-

m e n t i o n e d d i c h a l c o g e n l i g a n d s , other l i g a n d s , or other m e t a l c o m p l e x e s . W e expect these n e w m a t e r i a l s to e x h i b i t n o v e l stereochemistry, electrochemistry,

a n d u n u s u a l t r a n s p o r t or c a t a l y t i c p r o p e r t i e s .

In

rich the

f o l l o w i n g sections, w e s u m m a r i z e p a r t of o u r recent attempts i n synthes i z i n g these n e w materials a n d i n s t u d y i n g t h e i r i n t r i g u i n g c h e m i c a l a n d p h y s i c a l properties. TTT,

W e w i l l focus o n the three tetrathiolene

ligands

T T N , a n d T C T T N . It s h o u l d b e e m p h a s i z e d , h o w e v e r , that a l a r g e



-0.8

If -6.2

©^=©

04 i t |

is

2

i 2

2

3 k

3

4

3

!

0.2 f

3

04

2

3 If

(VS Ag/0.01 M Ag N 0 )

TCTTNPt (PPh ) O^0

4

I TTNPt (PPh3) 0^©©^l@br©

3 4

(PPh ) 0^=©

-0.6

"Of© 0.6

3 k

~08

©

4

^

1.0

®

Oxidation potentials (vs. Ag/O.OIM AgN0 ) of tetrathiolene ligands TTT, TTN, and TCTTN (top) and tetrathiolene complexes Pt (PPh ) TTT, Pt (PPh ) TTN, and Pt,(PPh ) TCTTN (bottom,)

TTTPtg

Figure 7.

1.0

T

© f © ll

T C T T N Q ^ ©


diplatinum-

POTENTIAL "(VOLTS)

372

INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES

II

n u m b e r of d i f f e r e n t types of reactions a n d p r o p e r t i e s are c o n c e i v a b l e f o r these d i - a n d t e t r a c h a l c o g e n - o r g a n o m e t a l l i c

compounds.

T h e s e are c u r -

r e n t l y u n d e r i n v e s t i g a t i o n a n d w i l l b e subjects of f u t u r e p u b l i c a t i o n s . Molecular

Metal Tetrathiolene

Clusters

B i m e t a l l i c t e t r a t h i o l e n e c o m p l e x e s of t h e g e n e r a l t y p e L

2 n

M (TTL) 2

c a n b e o b t a i n e d b y r e a c t i n g t w o moles of l o w - v a l e n t t r a n s i t i o n m e t a l complex L

n

+

W

M

( h e r e L a n d M refers to t h e l i g a n d s a n d t h e

metal,

r e s p e c t i v e l y ; t h e m - f n l i g a n d s L n e e d n o t b e i d e n t i c a l ) w i t h one m o l e


of t h e T T L ( w h e r e T T L =

T T T , T T N , or T C T T N ) ligands v i a oxida-

t i v e a d d i t i o n of the t w o s u l f u r - s u l f u r b o n d s to t h e t w o m e t a l (Equation 1).

2L structure (3)

atoms

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

m

+ n

M +

T T L -> L

2 n

M (TTL) + 2

c o m p r i s e d of a tetrathiolene

(TTL)

2mL

(1)

ligand bridging two

m e t a l complexes ( L M ) v i a f o u r m e t a l - s u l f u r b o n d s , t w o o n e a c h side of n

the m o l e c u l e as e x e m p l i f i e d i n F i g u r e 3a. T h e s o l u b i l i t i e s of these c o m p l e x e s i n c o m m o n o r g a n i c solvents rather

limited,

being

somewhat

soluble

are

in N,N'-dimethylformamide,

methylene chloride, a n d chloroform, sparingly soluble i n benzene, insoluble i n acetonitrile, precludes measurements

acetone, hexane,

etc.

The

and

limited solubility

s u c h as m o l e c u l a r w e i g h t d e t e r m i n a t i o n s .

Nev-

ertheless, the p r o d u c t s g e n e r a l l y p r e c i p i t a t e o u t of solvents s u c h as b e n zene

as m i c r o c r y s t a l l i n e solids a n d c a n b e

solvents

recrystallized w i t h

mixed

(1,3,4).

T h e I R s p e c t r a of the r e s u l t i n g c o m p l e x e s r e v e a l c h a r a c t e r i s t i c b a n d s w h i c h are d i a g n o s t i c of t h e p r e s e n c e of t h e T T L l i g a n d s . T h e s e b a n d s , h o w e v e r , are s h i f t e d f r o m those of the free l i g a n d s w h i c h o c c u r as f o u r s t r o n g features at: (or 7 1 4 ( w ) ) cm" cm"

1

1

(a)

1616(m),

for T T T ;

for T T N ; and (c)

TCTTN.

(b)

1317(m),

1304(s), 9 6 8 ( w ) ,

742(s)

I540(s), 1362(s), 1185(vs), 797(vs)

1528(s), 1428(s), 1299(vs), 854(m) c m "

S i m i l a r l y , the U V - v i s i b l e s p e c t r a of these c o m p l e x e s

features c h a r a c t e r i s t i c of t h e T T L l i g a n d s .

for

1

exhibit

I n fact, the colors of these

c o m p l e x e s p a r a l l e l those of t h e free l i g a n d s : the T T T , T T N , a n d T C T T N c o m p l e x e s are g e n e r a l l y green, r e d , a n d orange, r e s p e c t i v e l y . T h i s c o r r e lates w i t h the v i s i b l e a b s o r p t i o n s of the f r e e l i g a n d s w h i c h o c c u r at ( A in n m and c in M

1

c m ' i n parentheses):

1 0 ) , 583 ( s h , 3.08 X 1 0 ) , 471 (4.85 3

694 (6.39

1

3

1 0 ) , 637 (4.85

X

3

X 1 0 ) , 428 ( s h , 2.86 3

X

10 ),

3

4

4

X

10 ) 3

f o r T T N ( r e d ) ; a n d 423

(2.07

X

X and

3

403 ( s h , 1.54 X 1 0 ) f o r T T T ( g r e e n ) ; 420 (1.84 X 1 0 ) , 397 ( s h , 1.49 1 0 ) , a n d 377 ( s h , 8.60

m a x

X

10 ), 4

397 (1.58 X 1 0 ) , a n d 372 ( s h , 7.23 X 1 0 ) f o r T C T T N ( g o l d e n y e l l o w ) . 4

3


29.

TEO

Metal

373

Tetrathiolenes

T h e reactions of Vaska's c o m p o u n d s , £ r a n s - I r ( P P h ) ( C O ) X ( X = 3

CI,

2

B r , I), w i t h T T N i n b e n z e n e u n d e r reflux f o r 3 - 5 h r i n a 2:1 m o l a r ratio gave rise to o r a n g e complexes w h i c h a n a l y z e as ( P h P ) 2 ( C O ) X 2 l r 2 ( T T N ) 3

( E q u a t i o n 2) (4).

2Ir(PPh ) (CO)X + 3

2

T h e I R spectra r e v e a l e d t h e presence of c o o r d i n a t e d TTN->

2

(Ph P) (CO) X Ir (TTN) + 2PPh 3

2

2

2

2

(2)

3

C O , T T N , a n d P h P l i g a n d s . T h e c a r b o n y l s t r e t c h i n g f r e q u e n c y occurs at 3

2019, 2017, a n d 2005 c m " for X =

C I , B r , a n d I, r e s p e c t i v e l y , w i t h


1

fine

structures d e v e l o p i n g u p o n r e f l u x i n g . T h e f o u r T T N b a n d s , w h i c h analogous

f o r the

series,

occur

at

1532(s),

1340(s),

are

1190(m),

and

8 1 3 ( b r , w ) c m " . T h e intensities of the T T N b a n d s are c o m p a r a b l e w i t h 1

those of the P h P b a n d s for these complexes w i t h the T T N : P h P ratio of 3

1:2.

3

T h e e l e c t r o n i c spectra of ( P h P ) ( C O ) X I r ( T T N ) complexes i n 3

CH C1 2

2

2

2

2

are d o m i n a t e d b y t w o m a j o r b a n d s i n the v i s i b l e r e g i o n .

2

l o w e s t - e n e r g y b a n d , w h i c h occurs at 446 (2.42 X d 0 ) , 452 ( 2.52 X a n d 438 n m (2.62 X 1 0 M " c m " ) for X = 4

1

1

The 10 ),

4

4

C I , B r , a n d I, r e s p e c t i v e l y , is

m o r e or less insensitive to the n a t u r e of the h a l o g e n . O n the other h a n d , the s h o u l d e r - l i k e b a n d at h i g h e r energy w h i c h occurs at ( A c in M

in n m and

m a x

c m " i n parentheses) 318 ( s h , 1.42 X 1 0 ) , 349 ( s h , 1.27 X

1

1

10 ),

4

a n d 380 (sh, 1.61 X

10 )

for X =

4

4

C I , B r , a n d I, r e s p e c t i v e l y , is h i g h l y

h a l o g e n sensitive, b e i n g s h i f t e d to l o w e r energy a l o n g the sequence X

=

C I , B r , I. T h e U V b a n d s o c c u r at 270 n m (sh, 2.56 X 10 , 2.70 X 10 , a n d 4

3.17 X 1.0 for X =

C I , B r , a n d I, r e s p e c t i v e l y ) .

4

ammetry

studies r e v e a l e d t h a t

4

Preliminary cyclic volt-

these d i i r i d i u m clusters

undergo

one

irreversible oxidation and one irreversible reduction reaction. A series of d i p l a t i n u m t e t r a t h i o l e n e c o m p l e x e s c a n b e p r e p a r e d b y reacting P t ( P P h ) 3

i n b e n z e n e w i t h the c o r r e s p o n d i n g T T L l i g a n d i n a

4

m o l a r r a t i o of 2 : 1

( E q u a t i o n 3)

2Pt(PPh ) 3

+

4

The microcrystalline products,

(4).

T T L -> ( P h P ) P t ( T T L ) + 3

4

2

4PPh

w h i c h f o r m as green, r e d , a n d o r a n g e p r e c i p i t a t e f o r T T L = a n d T C T T N , r e s p e c t i v e l y , h a v e b e e n f o r m u l a t e d as b y e l e m e n t a l analysis.

(3)

3

TTT, T T N ,

(Ph P) Pt (TTL) 3

4

2

I R s p e c t r o s c o p y r e v e a l e d the presence

of b o t h

T T L a n d P h P l i g a n d s , w i t h the f o r m e r b e i n g m u c h w e a k e r i n b a n d 3

i n t e n s i t y t h a n the latter, a t t r i b u t a b l e to the 1:4 ratio of T T L : P h P . 3

f o u r s t r o n g T T L b a n d s o c c u r i n the c o m p l e x e s at 1 6 0 9 ( w ) , 954(vw),

and 740(m) cm"

1

f o r T T L — T T T ; at I 5 3 0 ( w ) ,

The

1276(s), 1346(m),

1 1 7 8 ( s ) , 8 1 8 ( w ) , a n d 8 0 8 ( s h ) c m " f o r T T L — T T N ; a n d at 1 4 6 5 ( w ) , 1

1392(w), 1239(s), a n d 8 3 6 ( w ) c m " for T T L — T C T T N . 1

The visible

spectra of the ( P h P ) P t T T L complexes h a v e t w o m a j o r b a n d s 3

4

2


with

374


v a r y i n g degrees of u n r e s o l v e d fine structure at ( A c m " i n parentheses):

PROPERTIES

II

in n m and e in M '

m a x

1

720 (1.80 X 1 0 ) , 652 ( s h , 1.03 X 1 0 ) , 440 w • s h ,

1

4

4

5.54 X 1 0 ) , a n d 387 ( s h , 1.05 X 1 0 ) f o r T T L = T T T ; 519 (1.44 X 1 0 ) , 3

4

4

490 (1.35 X 1 0 ) , 439 (1.43 X 1 0 ) , a n d 423 (1.43 X 1 0 ) f o r T T L — 4

4

4

T T N ; a n d 502 (1.24 X 1 0 ) , 447 (8.50 X 1 0 ) , a n d 409 (9.44 X 1 0 ) f o r 4

TTL =

TCTTN.

3

3

T h e s e v i s i b l e b a n d s are, i n general, s h i f t e d to l o w e r

energies i n c o m p a r i s o n w i t h t h e free l i g a n d s . I n o r d e r t o e s t a b l i s h u n a m b i g u o u s l y t h e stereochemistry

of these

m e t a l tetrathiolenes as w e l l as t h e m o d e of b i n d i n g of t h e t e t r a t h i o l e n e


ligands

to t r a n s i t i o n m e t a l

determinations

complexes,

of ( P h P ) P t ( T T N ) 3

4

single-crystal

and

2

x-ray

structural

(Ph P)2(CO) Br Ir (TTN) 3

2

2

2

were undertaken ( 3 ) . F i g u r e s 8 a n d 9 d e p i c t t h e structure of ( P h P ) P t ( T T N ) 3

ferent v i e w s . I t i n v o l v e s a t e t r a t h i o n a p h t h a l e n e

4

i n dif-

2

( T T N ) ligand bridging

t w o b i s - t r i p h e n y l p h o s p h i n e p l a t i n u m moieties w i t h e a c h p l a t i n u m a t o m being coordinated to t w o phosphorus ( f r o m t w o P P h

3

ligands) a n d t w o

s u l f u r ( f r o m t h e T T N l i g a n d ) atoms. T h e p l a t i n u m c o o r d i n a t i o n a n d t h e b r i d g i n g T T N l i g a n d (except, p e r h a p s , t h e s u l f u r a t o m s ) are close t o planarity.

T h e m o l e c u l e as a w h o l e , h o w e v e r , is b y n o means

planar.

T h e o v e r a l l distortions f r o m p l a n a r i t y c a n b e v i s u a l i z e d as a s m a l l r o t a t i o n of t h e s u l f u r atoms a b o u t t h e C ( 3 ) - C ( 3 ) ' b o n d , f o l l o w e d b y a l a r g e r o t a t i o n of e a c h

of t h e t w o p l a t i n u m c o o r d i n a t i o n planes

S • • • S edge, r e s u l t i n g i n t h e d i h e d r a l angles average planes f o r m e d b y n a p h t h a l e n e

about the

of 1 2 . 6 ° b e t w e e n t h e

group a n d

S(l)-C(l)-C(3)-

C ( 2 ) - S ( 2 ) a n d of 3 8 . 4 ° b e t w e e n t h e average planes f o r m e d b y S ( l ) C(l)-C(3)-C(2)-S(2) molecular geometry

a n d the P t S P 2

is c e n t r o s y m m e t r i c

2

coordination.

T h e resulting

w i t h t h e center of s y m m e t r y

l o c a t e d at t h e m i d p o i n t of C ( 3 ) a n d C ( 3 ) ' .

A n interesting observation

of t h e c r y s t a l structure of ( P h P ) P t ( T T N ) is that t h e i n t r a - a n d i n t e r 3

4

2

m o l e c u l a r F t • • • P t vectors f o r m p a r a l l e l arrays of z i g - z a g chains, w i t h the

former

(9.043(4) A ) being

substantially

longer

than

the

latter

(7.662(4) A ) . O n the other h a n d , t h e structure o f ( P h P ) ( C O ) B r I r ( T T N ) 3

2

2

2

2

is

a t o t a l surprise t o us ( 3 ) . O n c h e m i c a l as w e l l as s t e r e o c h e m i c a l g r o u n d s , one m i g h t expect t w o s q u a r e - p y r a m i d a l o r t r i g o n a l - b i p y r a m i d a l ( P h P ) 3

Br(CO)IrS (TTN)).

2

complexes

b r i d g e d b y the T T N l i g a n d (cf.

(Ph P) Pt 3

4

2

T h e d e t e r m i n e d structure of t h e f o r m e r c o m p o u n d , h o w e v e r ,

bears n o r e s e m b l a n c e t o t h e latter.

T h e t w o i r i d i u m s , i n s t e a d of o x i d a -

t i v e l y c l e a v i n g t h e t w o s u l f u r - s u l f u r b o n d s i n T T N , react w i t h o n l y o n e of t h e m , r e s u l t i n g i n a " b u t t e r f l y " a r r a n g e m e n t of the I r S 2

2

(from T T N )

f r a g m e n t . T h e m o l e c u l e is best d e s c r i b e d as t w o ( P h P ) ( C O ) B r l r m o i e 3

ties b r i d g e d b y t w o s u l f u r atoms ( S • • • S of 3.07 A ) f r o m T T N . T h i s u n u s u a l i r i d i u m d i m e r has a n I r - I r d i s t a n c e of 2.68 A w i t h t h e m e t a l -


29.

TEO

Metal

375

Tetrathiolenes

m e t a l b o n d c o n c e p t u a l l y o c c u p y i n g t h e s i x t h c o o r d i n a t i o n site of t h e highly distorted octahedral coordinations. T h e significance of t h e ( P h P ) P t ( T T L ) 3

r i c h e l e c t r o c h e m i s t r y (4). 9

+

complexes lies i n t h e i r

2

3

(n-C H )4N C104" in CH C1 4

4

C y c l i c voltammetry ( a 10~ M solution i n 0 . 1 M 2

2

u s i n g a s c a n rate of 200 m V / s e c , a p l a t i n u m

b e a d as w o r k i n g electrode, a p l a t i n u m w i r e as c o u n t e r electrode, a n d C(4)

C(5)


P(2)

P(l)' (b) Figure 8. The P Pt C S core of the [(C H ) P]t Pt (C H S ) molecule (ORTEP diagram, 50% probability thermal ellipsoids, infinity projection) with cry stalio graphic C I symmetry located at the midpoint between C(3) and C(3)'. (a) View along the normal of the naphthalene plane and (b) view similar to (a) but rotated 90° about the C(3)-C(3)' bond. k

2

10

h

6

5 3

f

2

10

Jt

If

r


INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES


376


II

29.

TEO

Metal

Ag/O.OIM A g N 0

3

377

Tetrathiolenes i n C H C N as reference 3

electrode)

r e v e a l e d t w o re-

v e r s i b l e one-electron oxidations at —0.51 a n d —0.28 V f o r (TTT)

(Ph P) Pt 3

4

2

(at ambient temperature) but four reversible one-electron oxida-

t i o n w a v e s at - 0 . 2 8 , ~ - 0 . 0 5 , ~ 0.01, a n d 0.31 V f o r ( P h P ) P t ( T T N ) 3

(at

ambient temperature).

4

T h e c y c l i c v o l t a m m o g r a m of

2

(Ph P) Pt 3

4

2

( T C T T N ) at a m b i e n t t e m p e r a t u r e turns o u t to b e m o r e c o m p l i c a t e d . H o w e v e r , at d r y ice/acetone t e m p e r a t u r e , i t exhibits t w o r e v e r s i b l e onee l e c t r o n o x i d a t i o n s at —0.02 a n d + 0 . 2 1 V a n d t w o q u a s i - r e v e r s i b l e o x i d a tions at + 0 . 5 8 a n d + 0 . 9 4 V . T h e s e o x i d a t i o n p o t e n t i a l s are s h i f t e d d r a m a t i c a l l y i n the n e g a t i v e d i r e c t i o n ( m o r e easily o x i d i z e d ) w i t h

respect


to the free l i g a n d s ( v i d e s u p r a ) as d e p i c t e d i n F i g u r e 7. T h i s is t a k e n as a n i n d i c a t i o n of a b u i l d u p of n e g a t i v e charge i n t h e T T L l i g a n d u p o n c o o r d i n a t i o n . T h e E P R s p e c t r a of the p a r a m a g n e t i c m o n o - a n d t r i c a t i o n s of ( P h P ) P t ( T T N ) i n d i c a t e d t h a t i n the m o n o c a t i o n t h e s p i n densities 3

4

2

are s u b s t a n t i a l l y l o c a l i z e d o n the T T N l i g a n d w i t h n o o b s e r v a b l e h y p e r fine i n t e r a c t i o n ( s ) w i t h the p l a t i n u m atoms, w h e r e a s i n the t r i c a t i o n there is a significant a m o u n t of s p i n densities " l o c a l i z e d " o n one p l a t i n u m a t o m ( n o n e q u i v a l e n t h y p e r f i n e i n t e r a c t i o n s ) e v e n t h o u g h the u n p a i r e d e l e c t r o n also resides m a i n l y o n the b r i d g i n g l i g a n d ( I ) . T h e s t e r e o c h e m i c a l n o v e l t y a n d the e l e c t r o c h e m i c a l richness of t h e b i m e t a l l i c tetrathiolene complexes p r o m p t e d us to synthesize a n d s t u d y l o n g e r chains of o l i g o m e t a l l i c t e t r a t h i o l e n e clusters. clusters ( D P P A ) P t ( T T L ) 4

4

3

(where D P P A =

The tetraplatinum

Ph C =

CPh ; T T L

2

2

—

T T T , T T N ) c a n b e p r e p a r e d b y r e a c t i n g s t o i c h i o m e t r i c e q u i v a l e n t s of the D P P A - b r i d g e d p l a t i n u m d i m e r P t ( D P P A ) ( P P h ) 2

2

3

s p o n d i n g t e t r a t h i o l e n e as s h o w n i n E q u a t i o n 4 ( 5 0 ) . 2Pt (DPPA) (PPh ) 2

2

spectroscopies

3

4

4

+ 3 T T L -> ( D P P A ) P t ( T T L ) 4

suggest the presence

4

w i t h the corre-

IR and UV-visible

3

of the t e t r a t h i o l e n e

+ 8PPh

3

(4)

a n d the bis-

p h o s p h i n e l i g a n d s . T h e s e c o m p o u n d s are i n g e n e r a l m o r e d e e p l y c o l o r e d a n d less s o l u b l e t h a n the d i p l a t i n u m c o m p l e x e s . s t r u c t u r e w i t h b r i d g i n g tetradentate

A zig-zag chain-like

T T L a n d bidentate D P P A ligands

d e p i c t e d i n 1 is e x p e c t e d f o r these t e t r a p l a t i n u m clusters. C y c l i c v o l t a m m o g r a m s of these t e t r a p l a t i n u m - t e t r a t h i o l e n e clusters i n d i c a t e d a c o m p l e x m a n i f o l d of o v e r l a p p i n g r e v e r s i b l e a n d q u a s i - r e v e r s i b l e o x i d a t i o n w a v e s l I I I I I I I i I I I (TTL) Pt (DPPA) Pt (TTL) Pt (DPPA) Pt (TTL) I I I I I I I I l I I l 2

2

1


378


PROPERTIES

II

( w h i c h a m o u n t to a t o t a l of a p p r o x i m a t e l y 12 e l e c t r o n transfers i n t h e case of ( D P P A ) P t ( T T N ) ) 4

4

(50).

3

L o n g e r h o m o - or h e t e r o n u c l e a r c h a i n - l i k e clusters s u c h as the h e x a m e t a l c o m p l e x 2 c a n b e p r e p a r e d b y r e a c t i n g the c o r r e s p o n d i n g m e t a l clusters w i t h a c o m b i n a t i o n of the tetrathiolenes m u l t i d e n t a t e l i g a n d s as b r i d g e s .

a n d other a p p r o p r i a t e

T h e m e t a l atoms M , M ' , a n d M " , t h e

t e t r a t h i o l e n e l i g a n d s , T T L , T T L ' , a n d the 1 b i d e n t a t e L L a n d 1' t e r m i n a l L

ligands need not be identical w i t h i n each group.

W e are

actively

p u r s u i n g the synthesis, structure, a n d e l e c t r o c h e m i s t r y of these u n u s u a l


cluster compounds. I I I I L i ' M " (TTL) ' M ' (LL) I I I l I I

I I

I l I I I I M (TTL) M (LL) , M ' (TTL) ' M " ^ * I i I i l i I I l i I I 2

Semiconducting

Organometallic

Polymers

I n a n a t t e m p t to synthesize n e w p l a n a r o r g a n o m e t a l l i c

complexes

w h i c h w i l l f o r m m u l t i p a r a l l e l c o l u m n a r stacks of s q u a r e - p l a n a r t r a n s i t i o n m e t a l c o m p l e x e s b r i d g e d b y a h i g h l y d e l o c a l i z e d o r g a n i c IT system, tetrathiotetracene

( T T T ) , tetrathionaphthalene

thionaphthalene

( T T N ) , a n d tetrachlorotetra-

( T C T T N ) were reacted

w i t h a v a r i e t y of 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 v a r y i n g degree of steric r e q u i r e m e n t s .

S i n c e car-

b o n y l s are c a p a b l e of s t a b i l i z i n g metals i n l o w f o r m a l o x i d a t i o n states and

are also s t e r i c a l l y q u i t e i n n o c e n t , m e t a l c a r b o n y l s w e r e c h o s e n

s t a r t i n g reactants f o r s u c h investigations ( 2 , 5 ) .

as

O u r initial goal was to

p r e p a r e b i m e t a l l i c c o m p o u n d s s u c h as N i ( C O ) ( T T L ) (cf. F i g u r e 3a) 2

4

w h i c h w i l l c o n c e i v a b l y f o r m c o l u m n a r s t a c k i n g v i a o v e r l a p s of the IT o r b i t a l s of the b r i d g i n g l i g a n d a n d / o r the m e t a l o r b i t a l s ( e i t h e r w i t h or w i t h o u t the i n v o l v e m e n t of the t e r m i n a l c a r b o n y l l i g a n d s ) .

Instead,

m u c h to o u r i n i t i a l surprise, w e o b t a i n a n e w class of p o l y m e r i c m e t a l tetrathiolene

c o m p o u n d s f o r m u l a t e d as

[Ni(TTL)]a. and

[Co (CO) 2

2

( T T L ) ] * f r o m the r e a c t i o n of the tetrathiolenes w i t h the c o r r e s p o n d i n g metal c a r b o n y l (phosphine) complexes.

These new organometallic poly-

mers e x h i b i t i n t e r e s t i n g s e m i c o n d u c t i n g p r o p e r t i e s (2,5).

T h e s e mate-

rials are d i s t i n c t l y different f r o m either the o r g a n i c c o n d u c t o r s s u c h as T T F - T C N Q ( 5 1 , 5 2 ) or the i n o r g a n i c c o n d u c t o r s s u c h as K P t ( C N ) • 2

X . 3 (53, 54, 55) 0

(where X =

4

C I , B r ) i n that the c h a i n d i r e c t i o n lies, p r e -

s u m a b l y , i n the m o l e c u l a r p l a n e ( a l o n g the l o n g m o l e c u l a r a x i s ) t h a n p e r p e n d i c u l a r to it.


rather

29.

TEO

Metal

379

Tetrathiolenes

Ni(CO)

4

+ TTN-» ^ [Ni(TTN)] + 4C0

(5)

x

T h e compound [ N i ( T T N ) ] # can be prepared b y reacting T T N w i t h excess n i c k e l t e t r a c a r b o n y l i n b e n z e n e ( E q u a t i o n 5 ) .

T h e dark b r o w n -

r e d a m o r p h o u s m a t e r i a l , i n s o l u b l e i n c o m m o n o r g a n i c solvents, exhibits n o c a r b o n y l s t r e t c h i n g f r e q u e n c i e s b u t f o u r s t r o n g T T N b a n d s at 1 5 2 8 ( s ) , 1338(s), (1320(sh)), 1185(m), and 800(m) c m ' A n e w b a n d also is o b s e r v e d at 965 c m "

1

1

i n the I R s p e c t r u m .

w h i c h can be attributed to

C • • • S b o n d s . T h e p o l y m e r i c c h a i n - l i k e structure 3 w a s p r o p o s e d f o r Downloaded by CORNELL UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch029

[Ni(TTN)]«. . . . Ni (TTN) Ni (TTN)

. . .

3 S i m i l a r l y , r e a c t i o n of T T N w i t h a s t o i c h i o m e t r i c a m o u n t of C o ( C O ) i n 2

b e n z e n e gave the p o l y m e r [ C o ( C O ) ( T T N ) ] 2

Co, (CO)

8

2

1

+ T T N ->

a ?

(Equation 6).

8

I R spec-

[Co (CO) ( T T N ) ] + 6 C O 2

2

(6)

x

t r o s c o p y i n d i c a t e d the presence of: ( 1 ) t e r m i n a l c a r b o n y l s ( b r o a d b a n d at 2 0 1 0 ( s ) ) ;

(2)

the c o o r d i n a t e d T T N l i g a n d at I 5 2 5 ( m ) ,

1339(m),

1 3 2 0 ( s h ) , 1 1 9 0 ( m ) , a n d 8 1 0 ( b r , w ) c m " ; a n d ( 3 ) a n e w b a n d at 970 c m " 1

w h i c h is p r o b a b l y a t t r i b u t a b l e to C • - • S s t r e t c h i n g f r e q u e n c i e s .

1

Again,

a p o l y m e r i c c h a i n - l i k e structure 4 w a s p r o p o s e d f o r [ C o ( C O ) ( T T N ) ] . . 2

. . . (TTN) Co (CO) (TTN) 2

2

2

a

. . .

4 T h e most i n t r i g u i n g p h y s i c a l p r o p e r t y of these p o l y m e r i c m a t e r i a l s is t h e i r e l e c t r i c a l c o n d u c t i v i t y . T h e t e m p e r a t u r e ( T ) d e p e n d e n c e of t h e p o w d e r resistance ( R )

c a n b e c h a r a c t e r i z e d b y the r e l a t i o n

w h e r e T is the square of the slope of the In R vs. T " 0

1 / 2

p l o t a n d is i n v e r s e l y

p r o p o r t i o n a l to the d e n s i t y of l o c a l i z e d states ( E q u a t i o n 8)

4a

T 0

(56,57,58).

=

=

kAN(e ) F


(8)

380

INORGANIC

Here a

COMPOUNDS W I T H UNUSUAL

PROPERTIES

is the r a d i u s o f the l o c a l i z e d state w a v e f u n c t i o n , N(e )

1

F

II

is t h e

d e n s i t y o f l o c a l i z e d states, A is the a r e a o f the c o m p r e s s e d p e l l e t , a n d k is B o l t z m a n n constant. P l o t s o f this t y p e h a v e b e e n o b s e r v e d f o r a n u m b e r o f k n o w n o n e - d i m e n s i o n a l systems a n d t a k e n as e v i d e n c e f o r oned i m e n s i o n a l h o p p i n g c o n d u c t i v i t y b e t w e e n l o c a l i z e d states (38-47,56F o r comparison, the hopping conductivity f o r a two-dimensional

64).

system c a n b e c h a r a c t e r i z e d b y the r e l a t i o n In R/R = ( T / T ) ~ 0

0

T

= 8a /(kDN(e )) 2

0

1 / 3

where

( h e r e D is t h e t h i c k n e s s ) , whereas t h e h o p p i n g

F

c o n d u c t i v i t y f o r a t h r e e - d i m e n s i o n a l system f o l l o w s the r e l a t i o n I n R/R

0


=

where T =

(T/T )~

1/4

0

0

T h i s t h e o r y has b e e n

!6a /(kN(e )). 3

F

ques-

t i o n e d r e c e n t l y b y M o t t (64). N e v e r t h e l e s s , this t y p e o f p l o t c a n b e u s e d to c h a r a c t e r i z e the c o n d u c t i v i t y of these materials.

T h e T values o f 1.7 0

X 10 K o b s e r v e d f o r b o t h c o m p o u n d s are, h o w e v e r , s i g n i f i c a n t l y h i g h e r 5

than that generally observed f o r one-dimensional conductors

or semi-

c o n d u c t o r s ( r a n g e : 0.5 - 5 X 1 0 K ) (24-26, 38-47, 56-64). 4

A m o r e c o n v e n i e n t p r e p a r a t i o n of the series of p o l y m e r s

[Ni(TTL)]#

( w h e r e T T L = T T T , T T N , o r T C T T N ) starts w i t h a 2 : 1 r a t i o o f N i (CO) (PPh ) 2

3

2

and T T L i n refluxing benzene ( E q u a t i o n 9) ( 5 ) . Simireflux

Ni(CO) (PPh ) 2

3

2

+ TTL

-j > - [ N i ( T T L ) ] , + 2CO + 2PPh

benzene

3

X

(9) l a r l y , the series o f c o b a l t tetrathiolene p o l y m e r s [ C o ( C O ) ( T T L ) ] a . 2

b e e n p r e p a r e d f r o m t h e r e a c t i o n of C o ( C O ) 2

benzene ( E q u a t i o n 10).

2

has

w i t h T T L i n refluxing

8

A l l of these materials e x h i b i t I R b a n d s i n d i c a -

t i v e o f the c o o r d i n a t e d l i g a n d s .

Co (CO) 2

8

+ TTL

reflux

-j > - [ C o ( C O ) ( T T L ) ] , + 6CO 2

benzene

2

(10)

X

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 of a l l these n e u t r a l o r g a n o m e t a l l i c p o l y mers f o l l o w s the same t e m p e r a t u r e d e p e n d e n c e as the T T N c o m p o u n d s ( E q u a t i o n 7 ) . T h e T values a n d the r o o m t e m p e r a t u r e r e s i s t i v i t y p , 0

s00

h o w e v e r , are s i g n i f i c a n t l y different for different tetrathiolene l i g a n d s . F o r the same T T L l i g a n d , the T a n d the p oo values are v e r y s i m i l a r d e s p i t e 0

the f a c t t h a t different metals

3

of v a r y i n g l o c a l geometries

(nickel vs.

d i c o b a l t d i c a r b o n y l m o i e t i e s ) are i n v o l v e d . I n g o i n g f r o m T T T t o T T N to T C T T N , t h e s l o p e - r e l a t e d

quantity T

0

=

1.1-5.6 X 10 K increases 5

o n l y s l i g h t l y (less t h a n or e q u a l to a f a c t o r of t w o ) whereas the r e s i s t i v i t y p oo increases b y one o r d e r of m a g n i t u d e i n e a c h step, g o i n g f r o m 1 0 t o 5

3

1 0 t o 1 0 o h m - c m (5). W e b e l i e v e t h a t this t r e n d is r e l a t e d to the o x i d a 6

7

t i o n p o t e n t i a l o f the T T L l i g a n d . T h a t is, since the o x i d a t i o n p o t e n t i a l s of the free l i g a n d s increase a l o n g t h e series T T T

< TTN
T T N - » T C T T N ) , the n e g a t i v e charges l o c a l i z e d o n the l i g a n d increase p r o g r e s s i v e l y . T h i s i m p l i e s that the n u m b e r of effective c h a r g e carriers ( o r the d e n s i t y of the d i s o r d e r e d l o c a l i z e d states) decreases as one goes f r o m T T T to T T N to T C T T N . T h i s t h e n causes a s l i g h t increase of a p p r o x i m a t e l y less t h a n or e q u a l to a factor of t w o i n T b u t a n e x p o n e n t i a l increase i n p o a l o n g the series T T T < T T N < T C T T N . 30

0

Both [ N ^ T T L ) ] ^ and [ C o ( C O ) ( T T L ) ] react w i t h o x i d i z i n g agents s u c h as i o d i n e either i n s o l u t i o n - s u s p e n s i o n or i n s o l i d - g a s phases, a c c o r d i n g to E q u a t i o n s 11 a n d 12, r e s p e c t i v e l y ( 5 ) . A suspension of the


2

2

~ [ N i ( T T L ) ] . . + 11 ±

| [Ni(TTL)I,],

2?

\ [Co (CO) (TTL)]. 2

i

2

2

a ?

?

(11)

± i [Co (CO) (TTL)I L 2

2

(12)

! /

complexes i n a b e n z e n e ( o r other o r g a n i c solvents) s o l u t i o n of i o d i n e w i l l a b s o r b m o l e c u l a r i o d i n e to f o r m [ N i ( T T L ) I ] a . a n d [ C o ( C O ) (TTL)I ] ( w h e r e y is the m o l a r ratio of i o d i n e to [ N i ( T T L ) ] « c a n d [ C o ( C O ) ( T T L ) ] . , r e s p e c t i v e l y ) . T h e r e s u l t i n g complexes are also i n s o l u b l e i n most o r g a n i c solvents. T h e same r e a c t i o n c a n b e c a r r i e d out i n s o l i d - g a s phase. T h e s o l i d [ N i ( T T L ) ] * or [ C o ( C O ) ( T T L ) ] * c o m plexes a b s o r b i o d i n e v a p o r s l o w l y at r o o m t e m p e r a t u r e t o f o r m [ N i ( T T L J I J a . or [ C o ( C O ) ( T T L ) I ] . T h e rate of these s o l i d - g a s reactions c a n be a c c e l e r a t e d b y i n c r e a s i n g t e m p e r a t u r e . F u r t h e r m o r e , these reactions are t o t a l l y r e v e r s i b l e i n the sense that the a b s o r b e d i o d i n e c a n be removed by p u m p i n g [ N i ( T T L ) I J * and [ C o ( C O ) ( T T L ) I ] under v a c u u m at e l e v a t e d temperatures. T h e k i n e t i c s of these s o l i d - g a s reactions c a n be m o n i t o r e d b y m e a s u r i n g the w e i g h t g a i n ( f o r w a r d reactions, E q u a t i o n s 11 a n d 12) a n d w e i g h t loss ( r e v e r s e d reactions, E q u a t i o n s 11 a n d 12) of the s o l i d complexes i n a n a t m o s p h e r e saturated w i t h i o d i n e vapor a n d i n vacuo, respectively ( 5 ) . y

y

2

2

2

x

2

a

2

2

2

2 /

2

; r

2

2

2 /

a ;

T h e I R spectra of these o x i d i z e d p o l y m e r s are v e r y s i m i l a r to those of the n e u t r a l p o l y m e r s except f o r a n e w b a n d at 1050 c m " w h i c h c a n reas o n a b l y be assigned to the f o r m a t i o n of n e w C = S b o n d s i n the o x i d i z e d p o l y m e r chains. 1

T h e r e v e r s i b i l i t y of these reactions suggests that t h e y are t o p o t a c t i c or i n t e r c a l a t i o n reactions.

We

b e l i e v e that these reactions

o x i d a t i o n of the p o l y m e r i c [ N i ( T T L ) ] * or

represent

[Co (CO) ,TTL]«, 2

2


chains

382

INORGANIC

COMPOUNDS WITH UNUSUAL

PROPERTIES

II

w i t h m o l e c u l a r i o d i n e w h i c h is c o n c o m i t a n t l y r e d u c e d to i o d i d e or p o l y i o d i d e anions w h i c h t h e n " i n t e r c a l a t e " i n t o the s o l i d m a t r i x . T o investigate the o x i d a t i o n states of [ N i ( T T L ) I ] a . a n d [ C o ( C O ) y

2

( T T L ) ^ ] ^ w e m e a s u r e d the resonant R a m a n spectra of where y =

2

[Ni(TTT)I ] 1 /

1,2,3. F o r [ N i ( T T T ) I ] , intense r e s o n a n c e - e n h a n c e d 3

s y m m e t r i c I—I—I s t r e t c h i n g f r e q u e n c y of I ~ was o b s e r v e d at 107

cm'

3

a l o n g w i t h the e x p e c t e d

overtone progressions

(65, 66).

a ?

totally

; r

1

T h i s is c o n -

sistent w i t h the f o r m u l a t i o n of [ N i ( T T T ) I " ] . F o r [ N i ( T T T ) I ] * o n the +

3

a ?

other h a n d , n o I ~ f r e q u e n c y w a s o b s e r v e d . T h o u g h the f a i l u r e to observe 3


the e x p e c t e d f r e q u e n c i e s

i n R a m a n spectroscopy does n o t constitute

a

p r o o f of the absence of the species, it is o u r b e l i e f t h a t the result is c o n sistent w i t h the f o r m u l a t i o n [ N i ( T T T )

y +

• y\~] f o r y < 1 since w e expect x

the [ N i ( T T T ) ] ^ c h a i n c h r o m o p h o r e to b e r e l a t i v e l y l i t t l e affected b y t h e o x i d a t i o n , a n d h e n c e the presence of y/3 h a v e b e e n easily detectable.

m o l e e q u i v a l e n t s of I ~ w o u l d 3

F o r [ N i ( T T T ) I ] ^ the resonance R a m a n 2

s p e c t r u m shows not o n l y the intense f u n d a m e n t a l a n d overtone p r o g r e s s i o n of I " b u t also the " a n t i s y m m e t r i c " stretch at 143 c m " , s u g g e s t i n g 1

3

either some d i s t o r t i o n of the t r i i o d i d e i o n f r o m the i d e a l i z e d D

x

h

sym-

m e t r y a n d / o r the presence of b o t h s y m m e t r i c a n d a s y m m e t r i c t r i i o d i d e ions

We

(65,66).

p r o p o s e that

[Ni(TTT)I ]* 2

can be formulated

as

( N i T T P • ( 1 / 2 ) 1 " • ( 1 / 2 ) I - ) * i n w h i c h the coexistence of I" a n d I " i n 3

3

the channels p r o v i d e d b y the o x i d i z e d [ N i ( T T T ) ]

; r

chains causes some

or a l l of the t r i i o d i d e ions to b e d i s t o r t e d . P r e l i m i n a r y e x t e n d e d x-ray a b s o r p t i o n fine structure

( E X A F S ) spectroscopic measurements

of t h e

o x i d i z e d p o l y m e r i c species also r e v e a l e d n o d i s t i n c t N i - I a n d Co—I b o n d s i n [ N i ( T T L ) I J , (nickel K edge) and [ C o ( C O ) ( T T L ) I ] , 2

edge),

r e s p e c t i v e l y , w h i c h is consistent

2

y

i o d i d e s or p o l y i o d i d e s are not d i r e c t l y b o n d e d to the m e t a l p o l y m e r chains

(cobalt

w i t h the f o r m u l a t i o n that

K the

tetrathiolene

(67).

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 d a t a of the o x i d i z e d species [ N i ( T T T ) I ] 1 /

(where y =

1,2,3) f o l l o w the same t e m p e r a t u r e d e p e n d e n c e

7 ) as the n e u t r a l species w i t h , h o w e v e r , a significant decrease i n T

0

f a c t o r of t w o to three a n d a d r a m a t i c decrease i n r o o m

a r

(Equation by a

temperature

r e s i s t i v i t y p o b y three orders of m a g n i t u d e i n g o i n g f r o m the n e u t r a l to 30

the o x i d i z e d p o l y m e r s . T h i s is consistent w i t h the increase i n the n u m b e r of effective charge carriers o n the o r g a n o m e t a l l i c c h a i n u p o n o x i d a t i o n . An

initially p u z z l i n g observation

[Ni(TTT)Iy]

that the

electrical conductivities

of

are v i r t u a l l y i n v a r i a n t to the d e g r e e of o x i d a t i o n w i t h y

=

1, 2, a n d 3 c a n n o w b e e x p l a i n e d b y t h e a b o v e f o r m u l a t i o n that f o r y >

1,

the extra i o d i n e s go i n as n e u t r a l i o d i n e m o l e c u l e s , c o n v e r t i n g p a r t (y

=

t 2 7

2 ) or a l l (y =

3) of the i o d i d e (I") i n t o the t r i i o d i d e ( I " ) 3

ions s u c h that

t h e o x i d a t i o n states of the n i c k e l tetrathiolene chains r e m a i n essentially the same for y > 1.


29.

TEO

Metal

383

Tetrathiolenes

Applications T h e r e are several p l a u s i b l e t e c h n o l o g i c a l a p p l i c a t i o n s of these n e w m e t a l tetrathiolene p o l y m e r s . A p r i m e e x a m p l e is the use of these o r g a n o m e t a l l i c p o l y m e r s as r e v e r s i b l e a n o d e m a t e r i a l s i n r e c h a r g e a b l e

(sec-

o n d a r y ) batteries.

these

W e take a d v a n t a g e of the f o l l o w i n g facts:

(1)

p o l y m e r s c a n b e o x i d i z e d w i t h oxidants s u c h as m o l e c u l a r i o d i n e reversibly;

(2)

b o t h the n e u t r a l a n d the o x i d i z e d species

are i n s o l u b l e i n

c o m m o n solvents; a n d ( 3 ) b o t h the n e u t r a l a n d the o x i d i z e d species t h e r m a l l y , air, a n d m o i s t u r e stable. Downloaded by CORNELL UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch029

process

of a b a t t e r y

are

W e reason that, i n t h e d i s c h a r g i n g

w i t h m e t a l tetrathiolene

p o l y m e r s as

reversible

anodes, electrons flow t h r o u g h the outer l o a d c i r c u i t ; the o x i d i z e d p o l y mers t h e n p i c k u p a n e q u i v a l e n t a m o u n t of i o d i d e or p o l y i o d i d e ions f r o m the electrolyte s o l u t i o n . I n the r e c h a r g i n g process, a n o p p o s i t e p o t e n t i a l is a p p l i e d w h i c h reduces t h e o x i d i z e d species to the n e u t r a l p o l y m e r s w i t h the c o n c o m i t a n t ejection of a n e q u i v a l e n t a m o u n t of the i o d i d e or p o l y i o d i d e ions b a c k to the electrolyte. A t y p i c a l rechargeable structed.

b a t t e r y b a s e d o n this i d e a has b e e n

con-

I t uses the [ N i ( T T L ) ] . p o l y m e r as the a n o d e , p o l y - 2 - v i n y l r

pyridine-iodine

(P2VP • (x/2)I ) 2

(68)

c o m p l e x as the c a t h o d e ,

aqueous K I s o l u t i o n as the electrolyte s o l u t i o n ( E q u a t i o n 1 3 ) .

and

I n the

d i s c h a r g i n g process, electrons flow f r o m the a n o d e [ N i ( T T L ) ] ^ to t h e c a t h o d e P 2 V P • (x/2)l

2

t h r o u g h the l o a d c i r c u i t ; the i o d i d e ( o r p o l y -

i o d i d e ) ions f o r m e d at the c a t h o d e t h e n enter the e l e c t r o l y t e w h i l e a n e q u i v a l e n t a m o u n t of i o d i d e ions f r o m the electrolyte s o l u t i o n i n t e r c a l a t e i n t o the o x i d i z e d m e t a l tetrathiolene p o l y m e r ( a n o d e ) .

The

electrolyte

c o n c e n t r a t i o n is therefore c o n s e r v e d . U p o n r e c h a r g i n g w i t h a n o p p o s i t e [Ni(TTL)],/KI(H 0)/P2VP •J I 2

p o t e n t i a l , these processes are r e v e r s e d .

2

(13)

Since b o t h the a n o d e a n d t h e

c a t h o d e are i n s o l u b l e i n the electrolyte, t h e o v e r a l l process amounts to t r a n s p o r t i n g i o d i n e f r o m P 2 V P p o l y m e r to m e t a l tetrathiolene p o l y m e r ( a r e d o x r e a c t i o n ) i n the d i s c h a r g i n g process a n d v i c e v e r s a i n the rec h a r g i n g process.

T h e m e a s u r e d v o l t a g e f o r s u c h a b a t t e r y ranges f r o m

0.5 to 0.8 V , d e p e n d i n g u p o n the t y p e of m e t a l t e t r a t h i o l e n e p o l y m e r chosen. It is c o n c e i v a b l e that h i g h e r voltages c a n b e a c h i e v e d b y c h a n g i n g the m e t a l a n d / o r the l i g a n d ( s )

of the a n o d e or b y r e p l a c i n g t h e

cathode w i t h more p o w e r f u l oxidizing materials. Conclusions I n c o n c l u s i o n , w e h a v e d e m o n s t r a t e d that the o r g a n o c h a l c o g e n c o m p o u n d s d i s c u s s e d i n the section o n " O r g a n o c h a l c o g e n L i g a n d s " are excel-


384

INORGANIC

COMPOUNDS

l e n t l i g a n d s f o r o r g a n o m e t a l l i c syntheses.

WITH UNUSUAL PROPERTIES

II

T h e resulting metal complexes,

e i t h e r as d i s c r e t e o l i g o m e r i c clusters o r i n f i n i t e - c h a i n p o l y m e r s , e x h i b i t novel stereochemistry a n d r i c h electrochemistry. T h e pseudo-one-dimens i o n a l s e m i c o n d u c t i v i t i e s a n d t h e r e v e r s i b l e t o p o t a c t i c o x i d a t i o n reactions of t h e i n s o l u b l e m e t a l t e t r a t h i o l e n e p o l y m e r s o p e n u p a n e w d i m e n s i o n of p o t e n t i a l t e c h n o l o g i c a l a p p l i c a t i o n s .

W e continue to develop the

c h e m i s t r y , s t e r e o c h e m i s t r y , a n d e l e c t r o c h e m i s t r y of these ( a n d r e l a t e d ) materials.


Acknowledgment I thank J. J . H a u s e r a n d P . K . G a l l a g h e r at B e l l Laboratories ( M u r r a y H i l l ) for permission to quote the conductivity a n d thermogravimetric results ( R e f . 5 ) , r e s p e c t i v e l y .

I a m also g r a t e f u l to J . S a n F i l i p p o at

R u t g e r s U n i v e r s i t y ( N e w B r u n s w i c k ) f o r laser R a m a n m e a s u r e m e n t s . S p e c i a l t h a n k s g o t o P . A . S n y d e r f o r h e r s k i l l f u l t e c h n i c a l assistance. I also e n j o y e d h e l p f u l discussions w i t h D . W . M u r p h y a n d J . N . C a r i d e s . O t h e r c o n t r i b u t o r s are a c k n o w l e d g e d i n R e f . 1,2,3, 4, a n d 5.

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