Cation radical salts based on Te-containing tetrachalcogenotetracenes

Physica t43B (I986) 304-306 North-HoUand, Amsterdam

304

CATION RADICAL SALTS BASED ON Te-CONTAINING TETRACHALCOGENOTETRACENES

Reizo KATO, and Hayao KOBAYASHI Department of Chemistry, Faculty of Science, Toho U n i v e r s i t y ,

Funabashi, Chiba 274, Japan

Akiko KOBAYASHI Department of Chemsitry, l l 3 , Japan

Faculty of Science,

The U n i v e r s i t y of Tokyo, Hongo, Bunkyo-ku,

Tokyo

The c r y s t a l of (DSeDTeT)2Br ( D S e D T e T = 5 , 6 - d i s e l e n o - l l , 1 2 - d i t e l l u r o t e t r a c e n e ) is i s o s t r u c t u r a l w i t h (TSeT)2CI. In the c r y s t a l , the d i s o r d e r e d DSeDTeT molecules form f a c e - t o - f a c e columns, which are i n t e r r e l a t e d to each o t h e r by the d i r e c t T e ( S e ) . . . T e ( S e ) contacts and S e ( T e ) . . . B r . . Se(Te) c o n t a c t s . This compound is a semiconductor w i t h small a c t i v a t i o n energy.

I.

INTRODUCTION The one-dimensional metal,

instability

in general,

has

which leads to the m e t a l - i n s u l a t o r

(semiconductor) t r a n s i t i o n

a t low temperature.

atoms in

the DSeDTeT and TTeT molecules w i l l

increase

band

following

ideas

have been suggested;

Increase in the d i m e n s i o n a l i t y d i s t o r t s like

Fermi

nesting.

For

surfaces

and

example,

TMTSF in

(1)

suppresses which

thelr sulfur

atoms in TMTTF are replaced by selenium atoms, and

BEDT-TTF

in

which

the

TTF

moiety

is

obtained

electrolyte N2.

of

the

by

disorder

breaks

charge d e n s i t y

wave

s t r u c t u r e and e l e c t r i c a l

(DSeDTeT)2Br

(

DSeDTeT =

resistivity

of

5,6-diseleno-ll,12-

The

ment

con-

A,

at ca. 70 <~C under

data: group

V=1679.3

(DSeDTeT)2Br;

P42/n, ~3,

Z=2.

a=18.534(5),

a=17.95(2),

(TTeT)2Br; c=5.382(3)

d.c.

four-probe

resistivity

measure--

used gold p a i n t contacts

the

leads.

of

(TTeT)2Br

has

resistivlty not

been

measureobtained,

because s u i t a b l e conducting p a i n t is not a v a i l -

Unsymmetrical exhibit

solutions

the

Reliable

=

to

by

and 25 um diameter gold wlres

(TTeT)2Br

5,6,11,12-tetratelluro-

of

needles

to the c r y s t a l s for

TTeT

crystal space

ments of (DSeDTeT)2Br

and p r e l i m i n a r y s t u d i e s of

(

black

oxidation

Tetragonal(twinning?),

ditellurotetracene) tetracene),

by the

~, v=1848.7 ~3

( f o r example, Nbl_xTaxSe3). 2 We r e p o r t here the crystal

fine

in b e n z o n i t r i l e

The

c=5.212(2)

introduced

synthesized

t a i n i n g the corresponding donor and supporting

provided the organic superconductors, l (2) Weak order

TTeT were as

electrochemical

Tetragonal,

long-range

interstack

r e p o r t e d methods.3, 4 (DSeDTeT)2Br and (TTeT)2Br were

extended by i n c o r p o r a t i n g the h e t e r o r i n g s , have unperiodicity

enhance

EXPERIMENTAL DSeDTeT and

plane--

and

interaction. 2.

As the s t r a t e g y to avoid such an i n s t a b i l l t y , the

wldth

DSeDTeT molecule

orientational

disorder.

is

expected Tellurium

0378 - 4363/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) and Yamada Science Foundation

able. 3. RESULTS

R. Kato et al.

/ Cation radical salts based on Te-containing tetrachalcogenotetracenes

305

S 0

3,554(4)

FIGURE 1 Crystal structure of (DSeDTeT)2Br

FIGURE 2 Mode of overlapping

a

Table I. Comparison of the Se(Te)-Se(Te) bond lengths and Se(Te)-Se(Te)-C bond angle. a

b

(TSeT)2CI 2.323(I) TTeT 2.673(I) (DSeDTeT)2Br 2.479(3) Table 2.

91.7(2),91.5(2) 87.7(2),87.5(2) 91.3(7),89.6(7)

(TSeT)2Cl 3.473 3.831 3.37 3.024/3.544

1 shows the

crystal

isostructural

with

that

of of

structure

(TSeT)?Br (DSeDTeT)2Br 3.49/3.50 3.554(4) 3.86 3.877(4) 3.42/3.45 3.47 3.14/3.14/3.56/3.55 3.161(3)/3.651(3)

of

phically

of

the

molecule

independent.

This

observe the DSeDTeT u n i t

along the c axis. The normal of the molecular

(DSeDTeT)2Br is

plane l a r g e l y t i l t s

(TSeT)2Cl.5

Mode of overlapping is i l l u s t r a t e d in Fig. 2.

The

DSeDTeT molecule is on the inversion center, half

Ref. 5 4

Comparison of the intermolecular i n t e r a c t i o n s .

(DSeDTeT)2Br. The crystal

and

Se(Te)-C

8

1.904(6),I.898(6) 2.114(7),2.111(7) 2.00(2),I.99(3)

Se(Te)°°,Se(Te) ( i n t r a s t a c k ) Se(Te).°,Se(Te) ( i n t e r s t a c k ) Interplanar spacing Se(Te)°°°Br(CI) distance

Figure

and

is

crystallogra-

means that

superposed

we

upon i t s

from the c axis (48.2 °).

In t h i s culumn, the i n t e r p l a n a r spacing is 3.47 and

short

intermolecular

Se(Te)oo,Se(Te)

distances (3..554 A) are observed. In

table

2,

the

intermolecular

Se(Te).o.

inverted image and Se and Te cannot be i d e n t i fied by X-ray crystallography. In the r e f i n e -

Se(Te) and Se(Te)°o°X (X;anion) distances are

ment of the structure,

The most c h a r a c t e r i s t i c

the chalcogen atom was

The Se(Te)-Se(Te) and Se(Te)-C distances and intermediate

angle

between

in those

DSeDTeTI/2+

are

of

(in

TSeTI/2+

those of

(TSeT)2X (X=Cl, feature

is

that

Br). the

donor columns are linked together by very short

treated as the superposition of Se and Te. Se(Te)-Se(Te)-C

compared with

(TSeT)2CI) and TTeT (neutral) (Table I ) . The DSeDTeT units form a uniform column

chalcogen.°,anion contacts, in addition to the d i r e c t chalcogen°.°chalcogen contacts. The low-temperature phase of (X=CI,Br)

is

considered to

the

(TSeT)2X

be semimetallic. 5

(TSeT)2Br prepared by us as a reference sample

306

R. Kato et al. / Cation radical salts based o~ Te-containing telrachalcogetiotetrace~t(,.~

~

-2 !

5 ~-3

I

~

Qe

,le

•

10Q

•i

I

••of•

•

e•

/

0

i

,,,,

Q

°,,~"

1i

.,,.,"

--4

J •. I

-5

I

I

I

I

....

I

0.5

2

~___

20

I0

T - I ( K --! i

. . . .30 ..

.

-

40

50

T l,/lO-3K-I FIGURE 3 R e s i s t i v i t y of (TSeT)2Br exhibited 38

"metallic

K after

which

temperature however,

conductivity" the

very

down to

resistivity

dependence

became

FIGURE 4 R e s i s t i v i t y of {DSeDTeT)2Br

of

rose.

the

slow

ca. The

this

to

successfully

ACKNOWLEDGEMENTS

hand,

(DSeDTeT)2Br

W.

conductor.

Although

The a u t h o r s are much g r a t e f u l

3). On

the

other

relatively

poor

observed d.c.

small

temperature

resistivity

was we

a

have

dependence of

around the

the

phase

compound

down t o 1.36 K ( F i g .

r e t a i n e d high c o n d u c t i v i t y

suppress

transition. 6

resistivity,

and

appears

the

room t e m p e r a t u r e ,

Sasakl,

Dr.

K•

Kajita,

N i s h i o of Toho U n i v e r s l t y conductivity

for

to and the

Professor Dr.

Y.

electrlcal

measurements•

REFERENCES

(DSeDTeT)2Br was s e m i c o n d u c t i v e at low temperature

(Fig.

4).

energy from

The

the

characteristic

low t e m p e r a t u r e

activation slope

is

ca.

I.

For r e v i e w , f o r example, J.M. Williams and K. C a r n e i r o , Adv. Inorg. Radiochem., 29 (1985) 249.

150 K. This o b s e r v a t i o n has i n d i c a t e d s i g n i f i cant

effect

disorder conduction atoms. izes that

of

has

disorder. been

path

In

this

introduced

constructed

system,

into

by

the

the

they

over a finite

cannot

length

contribute

local-

scale

so

to

the

d.c.

the

degree o f

conductivity. These

results

disorder

is

tion

the

of

disorder sense, fluorine

it

that

very important metallic

which

conduction

indicate

path is

does

not

would

TSeT molecule b r i n g s

the s t a b i l i z a Small

directly

degree o f

disturb

be p r e f e r a b l e .

indicative

substituent

for

state.

in

that

2. W.W. F u l l e r , P.N. C h a i k i n , and Phys. Rev. L e t t e r s 45 (1980) 43.

N.P.

Ong,

chalcogen

Such a l a r g e degree of d i s o r d e r electrons

the main

In

introduction

the 2 - p o s i t i o n

of

the this

3. K.A. Balodis, R.S. Medne, and O. Ya. N e i l a n d , Zh. Org. Khim., 20 (1984) 891. 4. D.J. Sandman, J.C. Stark, and B.M. Foxman, O r g a n o m e t a l l i c s , l (1982) 739. 5. I . F . Shchegolev and E.B. Yagubskli, ~n: Extended L i n e a r Chain Compounds, Vol. ed. J.S. M i l l e r (Prenum Press, 1982) 385. R.P. Shlbaeva, ibid., pp 435, r e f e r e n c e s c i t e d here.

Z, pp. and

of a the

(maybe weak) d i s o r d e r and

6. B. H i l t i , C.W. Mayer, G. Rihs, H. L o e l i g e r , and P. B a l t z e r , Mol. C r y s t . Liq. Cryst., 120 (1985) 267.