New donors for organic metals

Synthetic Metals, 19 (1987) 5 6 9 - 5 7 2

NEW DONORS

FOR O R G A N I C

TOYO N A R I

SUGIMOTO,

ZEN-ICHI

YOSHIDA

Department

569

METALS

HIROSHI

of S y n t h e t i c

AWAJI,

IWAO SUGIMOTO,

Chemistry,

YOHJI

K y o t o University,

MISAKI

Kyoto

and

606

(Japan)

ABSTRACT Six kinds sp

2

carbons

of new d o n o r s are

inserted

1,3-dithiol-2-ylidene framework,

were

potentials

between

formers

have

temperature

moieties

synthesized.

was o b t a i n e d

and TTF,

ability

or four

into c y c l o b u t a n e y l i d e n e of the first o x i d a t i o n

it was

to the

shown

latter.

that

the

The new donors

salts on c o m p r e s s e d

S/cm. In p a rt i c u l a r ,

crystal,

temperature

two or t h r e e

TCNQ or T C N Q F 4, and the r o o m

of the

- 0.8

as a single

with d e c r e a s i n g

are c o m b i n e d

salts w i t h

conductivities

in the range of 0.03

formally

From comparison

donating

transfer

in w h i c h

two 1 , 3 - d i c h a l c o g e n o l e s

the new d o n o r s

superior

formed c h a r g e

(i - 6),

between

pellets

the 1 - TCNQ

and the c o n d u c t i v i t y

in the range

of 300

were salt

increased

(16 S/cm)

and 200 K

(23 S/cm).

INTRODUCTION TTF and its c h a l c o g e n important salts.

donor

Nevertheless,

skeletal

structures

accomplishment

analogs

for c o n d u c t i n g

development from TTF,

of o r g a n i c

in kind and quantity.

(TSF and TTeF)

and

of new donors

is b e i n g

conductors

In this paper

six kinds

of new donors

2-ylidene

moieties:

containing

serve

superconducting

having

required

1,3-dithiol-

the

0379-6779/87/$3.50

different

superconductors synthesis

ethanediylidene-2,2'-bis(l,3-dithiole)

(3),

of

or 1 , 3 - d i s e l e n o l -

ethanediylidene-2-(l,3-dithiole)-2'-(l,3-diselenole) diylidene-2,2'-bis(l,3-diselenole)

transfer

for u l t i m a t e

and f u t h e r m o r e is d e s c r i b e d

as a m o s t

charge

(2),

(i), ethane-

1,4-cyclohexenylidene-2,2'-

© Elsevier Sequoia/Printed in The Netherlands

570 bis(l,3-dithiole)

(4), t e t r a k i s ( l , 3 - d i t h i o l - 2 - y l i d e n e ) c y c l o b u t a n e

(5) and t e t r a k i s ( l , 3 - b e n z o d i t h i o l - 2 - y l i d e n e ) c y c l o b u t a n e charge transfer

(6), whose

salts are expected as a new type of organic

conductors. RESULTS New donor synthesis The synthesis of 1 - 3 was achieved by using the Wittig reaction of

(4,5-dicarbomethoxy-l,3-dithiol-

or 1,3-diselenol-2-ylidene)-

phosphorane with 2 - f o r m y l m e t h y l e n e - 4 , 5 - d i c a r b o m e t h o x y - l , 3 - d i t h i o l e or 1,3-diselenole resulting

and further by d e c a r b o m e t h o x y l a t i o n

tetracarbomethoxy

derivatives

of the

[1,2]. The t e t r a c a r b o m e t h o x y

4 was already synthesized by Cava et al.

[3], so that it was

decarbomethoxylated

The tetracarbomethoxy-

by the method above.

dibenzo-l's were converted

to the corresponding

which were subjected to reductive Ni(PPh3)4/Zn-Cu octacarbomethoxy

couple to give 5 derivative)

s ES~\~_.<~ ~

cyclodimerization

Se

S

(1)

R-~S

Se

(3)

R

S

of the

[4].

...Se

(2)

S

by aid of

(after d e c a r b o m e t h o x y l a t i o n

and 6, respectively

and

dibromo derivatives,

R

S"~R (5) R = H

(4_) Electrochemical

R"~.S S./~R R R

¢6_) R---¢¢.=C~h-

properties

In order to estimate

the donating ability of ~ - 6, their

oxidation potentials were m e a s u r e d by using cyclic voltammetry (see Table i). The new donors except oxidation potentials indicating

for 6 have the lower first

(E 1 ) than that of TTF

(+0.34 V

us.

Ag/AgCI),

that the formers are superior donors to the latter.

571 TABLE 1 The o x i d a t i o n p o t e n t i a l s a Donor

E1

E2

1

+0.20 b

+0.36 b

0.16

2

+0.26 b

+0.40 b

0.14

3

+0.33 b

+0.47 b

0.14

4

E3

E4

E2 - E1

+0.23 b

5

+0.19 c

6

+0.43 b

aV us. Ag/AgCI.

(+0.98) c" d (+i. 30) c +0.72 b

(+1.40) b

b M e a s u r e d in CH3CN.

means an i r r e v e r s i b l e

Charge-transfer

%0 ~0 ~0

C M e a s u r e d in CH2CI 2.

a( )

step.

salts w i t h TCNQ or TCNQF 4

Table 2 shows the c o m p o s i t i o n and e l e c t r i c a l p r o p e r t i e s of charge transfer salts between the new donors and TCNQ or TCNQF4, p r e p a r e d by m i x i n g method.

The room t e m p e r a t u r e c o n d u c t i v i t i e s on c o m p r e s s e d

pellets are c o n s i d e r a b l y high the a c t i v a t i o n energies

(0.03 - 0.8 S/cm).

It is noted that

are very low for all the salts. The single

crystal p r e p a r a t i o n by d i f f u s i o n m e t h o d was first of all carried out for the 1 - TCNQ salt. From change of the r e s i s t a n c e by t e m p e r a t u r e as shown in Fig.

i, the single crystal is m e t a l l i c

in

the t e m p e r a t u r e range of 300 - 200 K, and the m a x i m u m c o n d u c t i v i t y is 23 S/cm.

However,

b e l o w 200 K the c o n d u c t i v i t y sharply decreases

and this crystal becomes

semiconductor

[5].

TABLE 2 The c o m p o s i t i o n and e ~ e c t r i c a l p r o p e r t i e s of CT c o m p l e x e s b e t w e e n n e w donors and TCNQ or TCNQF 4 Donor

Acceptor

D:Aa

CRT

(S/cm)°

Ea

(eV) C

1

TCNQ

i:i

0.79

2

TCNQ

2:3

0.072

0.046

3

TCNQ

2:3

0.24

0.038

4

TCNQ

i:i

0.26

0.062

5

TCNQ

1:2

0.032

0.057

TCNQF 4

i:I

0.07~

a D e t e r m i n e d by the e l e m e n t a l analysis, p e l l e t by u s i n g f o u r - p r o b e method.

0.09 - 0.4

0.04 - 0.06

b M e a s u r e d on c o m p r e s s e d

CE a =

(103kA)/(log e)

•

where

A is the slope of s t r a i g h t line o b t a i n e d by p l o t t i n g log R w i t h r e s p e c t to

(1000/T).

572 1" 1(30

30(3 2Q(3

(K)

~

~--:'"" .... ' ....

."" ./

t

'

L

.

z

--

°:"

.7 .:

m+

:..:/ - ". +

~

.-~

-

.-:Y

~

-

::: s:-"-

103

] J

I

102

5

10

15

20

IO00/T

Fig. I. The plot of resistance (R, ohm) vs. for a single crystal of ~ - TCNQ complex.

1000/T

(l/K)

ACKNOWLEDGEMENTS We are deeply indebted to Prof. K. Imaeda

technical Laboratory), University)

H. Inokuchi,

(Institute of Molecular Science), Prof.

I. Tsujikawa

Dr. T. Enoki,

Dr. H. Anzai

and Dr. N. Kojima

for their kindness of electrical

Dr.

(Electro(Kyoto

conductivity m e a s u r e m e n t

REFERENCES 1

Z. Yoshida, S. Yoneda,

2

T. Kawase, Tetrahedron

Z. Yoshida,

H. Awaji,

H. Awaji,

I. Sugimoto,

Lett.~ (1983)

T. Sugimoto,

and

3469.

and T. Sugimoto,

Tetrahedron

Lett.~ (1984)

4227. 3

M. Sato, N. C. Gonnella,

and M. P. Cava, J. Or~. Chem.,

44

(1974)

930. 4

T. Sugimoto, and N. Kasai,

5

T. Sugimoto, Yoshida,

H. Awaji,

Y. Misaki,

J. Am. Chem. H. Awaji,

and H. Anzai,

Soc.,

Z. Yoshida, 107

I. Sugimoto,

(1985)

T. Kawase,

in preparation

Y. Kai, H. Nakagawa,

5792. S. Yoneda,

for publication.

Z.