New electron donors: BEDT-TTF derivatives bearing a pyridine group; synthesis, crystal structure, electrochemical studies and the formation of charge transfer complexes

Article abstract of DOI:10.1039/a900063a

Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives 1a,b and 2a,b containing a pyridine group have been synthesized and their redox potentials have been studied by cyclic voltammetry in dichloromethane solution, which indicate that they are weaker electron donors than BEDT-TTF. Compound 2b has been studied by X-ray crystallography, which revealed a column-packing pattern in its crystal lattice. The charge transfer (CT) complexes formed between these new donors and tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyanobenzo-1,4-quinone (DDQ) as well as cupric chloride (CuCl2) have been investigated. Among them the CT complexes 1b_1.1*TCNQ and 1a*CuCl2 show conductivity in the semiconducting range at room temperature (?_rt=1.6*10^-3 S cm^-1 for 1b_1.1*TCNQ, 4.3*10^-3 S cm^-1 for 1a*CuCl2 measured on a compressed pellet). From the results of X-ray photoelectron spectroscopy (XPS) and conductivity measurements, we suggest that charge transfer and coordination contact coexist in the complex 1a*CuCl2.

Full text of DOI:10.1039/a900063a

J O U R N A L O F
New electron donors: BEDT-TTF derivatives bearing a pyridine
group; synthesis, crystal structure, electrochemical studies and the
formation of charge transfer complexes
Wei Xu,* Deqing Zhang, Hongxiang Li and Daoben Zhu
C H E M I S T R Y
Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080,
P.R. China
Received 4th January 1999, Accepted 26th March 1999
Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives 1a,b and 2a,b containing a pyridine group have been
synthesized and their redox potentials have been studied by cyclic voltammetry in dichloromethane solution, which
indicate that they are weaker electron donors than BEDT-TTF. Compound 2b has been studied by X-ray
crystallography, which revealed a column-packing pattern in its crystal lattice. The charge transfer (CT) complexes
formed between these new donors and tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyanobenzo-1,4-
quinone (DDQ) as well as cupric chloride (CuCl ) have been investigated. Among them the CT complexes
2
1
1
b
·TCNQ and 1a·CuCl show conductivity in the semiconducting range at room temperature (s =
1
.1
2
rt
.6×10−3 S cm−1 for 1b ·TCNQ, 4.3×10−3 S cm−1 for 1a·CuCl measured on a compressed pellet). From the
1.1
2
results of X-ray photoelectron spectroscopy ( XPS) and conductivity measurements, we suggest that charge transfer
and coordination contact coexist in the complex 1a·CuCl .
2
Introduction
Results and discussion
Since discovery of the first organic metal TTF–TCNQ (TTF:
tetrathiafulvalene, TCNQ: tetracyanoquinodimethane) in
Synthesis of BEDT-TTF derivatives
Synthesis of the target molecules 1a,b and 2a,b started from
1
972,1 great progress has been achieved in the field of organic
trithione oligomer (C S ) , oligo(4,5-dihydro-1,3-dithiole-
conductors and superconductors.2 Nowadays, efforts are still
being devoted to the chemical modification of the donor of
the TTF series, for enhancement of the intermolecular inter-
actions among electron donors and acceptors (or counter
anions), which is essential for stabilizing the conducting and
superconducting state (suppressing the Peierls distortions) at
low temperature. Such studies include replacing the sulfur
atoms of TTF by more orbitally diffuse selenium atoms (e.g.
tetramethyltetraselenafulvalene, TMTSF)3 and substituting
the four hydrogen atoms by sulfur rich substituents (e.g. bis-
3 5 x
2
,4,5-trithione), as shown in Scheme 1, which was prepared
by the oxidation of bis(tetrabutylammonium) bis[2-thioxo-
,3-dithiole-4,5-bis(thiolato)]zincate with iodine.7 This olig-
1
omer undergoes thermal depolymerization on heating to give
the unstable 4,5-dihydro-1,3-dithiole-2,4,5-trithione monomer,
which acts as an effective 4p component to form Diels–Alder
adducts with dienophiles.8 Accordingly, the oligomer reacted
with 4-vinylpyridine and 2-vinylpyridine leading to the key
intermediate compounds 3a and 3b in yields of 15 and 20%
after recrystallization. Compounds 3a and 3b were converted
to compounds 4a and 4b by a conventional method9 in high
yield. The cross coupling reaction of 4,5-ethylenedithio-1,3-
dithiole-2-thione10 and compounds 4a,b in the presence of
triisopropyl phosphite afforded the target compounds 1a and
(
ethylenedithio)tetrathiafulvalene, BEDT-TTF)4 to increase
the chance of contact. These efforts have led to the discovery
of more than forty organic superconductors with a highest
critical temperature of 12.8 K.5 Another trend developed
recently is introducing a hydroxy group or other functional
groups into donor molecules to set up intermolecular hydrogen
bonds2b,6 to increase the intermolecular interactions in the
materials. From a similar consideration, our project is aimed
at introducing a coordination group such as pyridine into the
BEDT-TTF molecule to enhance the intermolecular inter-
actions between electron donors and counter anions in the
crystal of their charge transfer (CT) complexes by the forma-
tion of coordination bonds between the coordination groups
and the metallic atoms of counter anions. Furthermore, such
electron donors containing coordination groups may form
special supermolecular structures with inorganic metallic ions
through the coordination effect (self-assembly). Recently, for
studies on conducting Langmuir–Blodgett (LB) films,7 J. Y.
Becker et al. prepared several ethylenedithiotetrathiafulvalene
1
b in yields of 26 and 25% after recrystallization from 1,2-
dichloroethane. The homo-coupling products of 4a,b have
been observed in the mass spectra of the reaction mixture, but
have not been isolated; they are expected to be a mixture of
isomers. The above coupling reaction was also conducted
using 4,5-ethylenedithio-1,3-dithiol-2-one instead of the corre-
sponding thione, but isolation of the target compounds was
much more difficult due to the formation of side products
such as BEDT-TTF. In contrast, in the coupling reaction
with 4,5-ethylenedithio-1,3-dithiole-2-thione the formation of
BEDT-TTF was largely suppressed.
Dehydrogenation of 1a and 1b was carried out by treatment
with an excess of DDQ in refluxing xylene (mixture of isomers)
to give compounds 2a and 2b in yields of 20 and 44% after
chromatography on silica gel with dichloromethane–ethyl acet-
ate (151). Charge transfer complexes were found to be formed
during the reaction, which lowered the reaction yields.
In the 1H-NMR spectra of 3b and 4b a typical ABX
hydrogen–hydrogen coupling system was observed, a quad-
ruplet for the pyridine ring linked methine proton ( X) (d=
4.90–5.10 ppm) and four doublets for the adjacent methylene
protons (AB) (d=3.60–3.95 ppm). For compounds 3a and 4a
(
EDT-TTF) derivatives bearing a pyridine or N-methylpyri-
dine group as a hydrophilic tail, which should be favorable
for the formation of LB films. In this paper we will report the
synthesis, crystal structure and electrochemical studies on new
electron donors (1a,b and 2a,b) containing a pyridine group.
We will also discuss preliminary investigations on their CT
salts formed with TCNQ and 2,3-dichloro-5,6-dicyanobenzo-
1
,4-quinone (DDQ) as well as cupric chloride (CuCl ).
2
J. Mater. Chem., 1999, 9, 1245–1249
1245

S
S
S
S
R
S
S
S
S
R
effect of conjugation and the electron withdrawing behavior
of pyridine. From the data in Table 1, it can also be concluded
that the substituent position of the pyridine has no significant
effect on the electrochemical behavior of these BEDT-TTF
derivatives.
S
S
S
S
S
S
S
S
1
a R =
b R =
2a R =
2b R =
Crystal structure of 2b
N
N
Crystallographic data of 2b are presented in the Experimental
section and selected bond lengths and angles are listed in
Table 2. Fig. 1 shows the molecular structure of 2b.
Apparently, compound 2b in the crystal adopts a non-planar
conformation. The TTF moiety shows a boat conformation,
folding along the S(3),S(4) and S(5),S(6) vectors by 10.7
and 27.2° respectively. The planar pyridine ring forms a
dihedral angle of 26.3° with the adjacent S(7)C(9)C(10)S(8)
moiety. The C(7)C(8)S(8)C(10)C(9)S(7) ring is folded along
the S(7),S(8) vector by 40.0°. The bond lengths and angles
of 2b are all in the normal range, and are similar to those of
BEDT-TTF.11 The bond length of C(9)–C(10) is 1.329(7) A,
typical for carbon–carbon double bonds,12 which further
confirms the dehydrogenation position.
In the crystal lattice of 2b (Fig. 2), molecules are stacked in
columns. Interestingly, ‘BEDT-TTF’ and the pyridine moiety
of 2b are arranged in two columns separately. Within the
1
N
N
S
S
S
S
S
S
S
Zn
S
4
Bu N
S
S
2
˚
I
2
, EtOH
acetone, –50 °C, 2 h
7%
S
S
S
S
9
S
n
(
C S )
3 5 x
‘
3
BEDT-TTF column’, short S,S contacts in the range
˚
.425(1)–3.554(1) A are observed and neighboring molecules
are displaced toward each other. In the ‘pyridine column’
adjacent pyridine rings are planar with an inter-planar distance
of about 3.818 A. Thus, if the pyridine part of the compound
2b is considered to be an electron acceptor, the crystal structure
of 2b is very similar to those of organic conductors and
superconductors.
Hx
S
S
S
N
S
R
S
R
Hg(AcO)
2
˚
S
O
CHCl
3
S
Ha
Hb
S
dioxane
5 °C
S
7
3
a-b
4a-b
Charge transfer complexes
S
S
S
a R =
b R =
By directly mixing 1a or 1b with TCNQ or DDQ black
polycrystals or powders were obtained. These should be the
CT complexes formed between 1a (or 1b) with TCNQ (or
DDQ). The stoichiometric ratio of these CT complexes was
determined based on elemental analysis as indicated in Table 3.
Their room-temperature conductivities measured on a com-
pressed pellet are also listed in Table 3, and only the conduc-
tivity of the complex 1b ·TCNQ was in the semi-conducting
range. The cyano group stretching frequencies of the TCNQ
complexes of 1a and 1b (Table 3) are shifted to low wave-
numbers with respect to that of TCNQ (2222 cm−1); this is
due to the influence of the delocalised radical anion in the
complex.13
When 2a and 2b were treated with TCNQ and DDQ under
the same conditions as for 1a and 1b, no black precipitate was
obtained. This observation suggested that the electron
donating abilities of 2a and 2b were lower than those of 1a
and 1b, which was fully in accordance with the results of
electrochemical studies.
S
S
DDQ
N
N
1
2
(
isoPrO)
3
P
xylene
reflux
Scheme 1
1
.1
as well as 1a and 1b, however, the methylene protons (AB)
were found to be a doublet.
Electrochemical studies
The redox potentials of new electron donors 1a,b and 2a,b
were measured in dichoromethane by cyclic voltammetry.
Their cyclic voltammetric data are collected in Table 1 together
with those of BEDT-TTF for comparison. For 1a and 1b as
well as 2a and 2b, two reversible single-electron oxidation
waves are observed, corresponding to E1/2 and E1/2 in Table 1.
The values of 1a and 1b are slightly raised as compared to
those of BEDT-TTF, which is probably due to the electron
withdrawing effect of the pyridine units. The results also
indicate that 2a and 2b are even more difficult to oxidize than
In addition, we also conducted a preliminary study of the
complexes of these new donors with metallic compounds,
taking advantage of the coordination ability of the pyridine
group. As an example, the complex formed between 1a and
CuCl ·2H O in dichloromethane was studied by X-ray photo-
1
2
2
2
1
a and 1b. This may be accounted for by the cooperative
electron spectroscopy ( XPS). The binding energies (BE) of
Cu(2p ), Cl(2p ), N(1s) and S(2p ) in the complex,
3
/2
3/2
3/2
compound 1a and CuCl are listed in Table 4. There are two
Table 1 Cyclic voltammetric data of 1a,b and 2a,b (10−4 mol l−1 in
2
kinds of sulfur atoms with different BE (166.17 and 163.90 eV)
CH Cl , TBAPF as supporting electrolyte, Pt electrode as working
2
2
6
in the complex in the approximate ratio of 1511, and the
former has a significantly increased energy while the latter
remains at almost the same energy as in 1a. This result may
suggest that charge transfer occurs between parts of the donor
molecules and copper chloride, which is further confirmed by
the conductivity measurement for this complex (Table 3). The
electrode, scan rate 50 mV s−1, reported voltage vs. SCE)
E/V
1a
1b
2a
2b
BEDT-TTF
E1/2
E1/2
0.45
0.82
0.45
0.87
0.50
0.89
0.48
0.89
0.43
0.84
1
2
1
246
J. Mater. Chem., 1999, 9, 1245–1249

˚
Table 2 Selected bond lengths (A) and angles (°) for compound 2b
S(1)–C(1)
S(3)–C(3)
S(3)–C(5)
N–C(11)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(7)–C(8)
1.759(6)
1.744(5)
1.760(5)
1.396(7)
1.491(9)
1.342(7)
1.323(6)
1.332(7)
S(6)–C(8)
S(6)–C(6)
S(7)–C(7)
S(7)–C(9)
S(5)–C(6)
S(5)–C(7)
S(8)–C(10)
S(8)–C(8)
1.736(5)
1.762(5)
1.737(5)
1.796(5)
1.750(5)
1.764(5)
1.743(5)
1.763(5)
S(4)–C(4)
S(4)–C(5)
S(2)–C(4)
S(2)–C(2)
S(1)–C(3)
C(9)–C(10)
C(9)–C(11)
C(11)–C(12)
1.741(5)
1.745(5)
1.746(5)
1.797(6)
1.739(5)
1.329(7)
1.463(6)
1.342(7)
C(8)–S(6)–C(6)
C(7)–S(7)–C(9)
C(10)–S(8)–C(8)
C(4)–S(4)–C(5)
C(4)–S(2)–C(2)
C(3)–S(1)–C(1)
C(11)–N–C(15)
C(2)–C(1)–S(1)
C(4)–C(3)–S(1)
92.3(2)
98.5(2)
99.9(2)
C(3)–C(4)–S(4)
C(3)–C(4)–S(2)
C(6)–C(5)–S(3)
S(4)–C(5)–S(3)
C(5)–C(6)–S(5)
C(5)–C(6)–S(6)
C(8)–C(7)–S(7)
C(8)–C(7)–S(5)
S(7)–C(7)–S(5)
117.0(4)
127.5(4)
122.4(4)
113.7(3)
123.9(4)
123.3(4)
125.6(4)
115.3(3)
118.9(3)
C(7)–C(8)–S(6)
C(7)–C(8)–S(8)
S(6)–C(8)–S(8)
C(10)–C(9)–C(11)
C(10–C(9)–S(7)
C(11)–C(9)–S(7)
C(9)–C(10)–S(8)
C(12)–C(11)–N
118.9(4)
120.9(3)
119.7(3)
124.9(4)
121.1(4)
114.0(3)
124.7(4)
122.9(4)
95.6(2)
101.0(3)
101.8(3)
117.8(5)
115.0(5)
129.2(4)
and counter anions by electrochemical and diffusion methods
is also in progress.
Summary
Four novel pyridine-substituted BEDT-TTF derivatives (1a,b
and 2a,b) were synthesized and characterized. Their redox
potentials were determined by cyclic voltammetry in CH Cl
2
2
solution and the results revealed that they were weaker donors
than BEDT-TTF. A crystal structure analysis was carried out
for compound 2b; an interesting molecular packing pattern
was observed. Preliminary results on CT complexes of these
Fig. 1 Molecular structure of compound 2b.
new donors with TCNQ and DDQ as well as CuCl are
2
presented. Further investigations on CT complexes based on
these new donors are in progress.
Experimental
X-Ray crystallography†
A single crystal of 2b with the size of 0.4×0.4×0.15 mm
suitable for X-ray structure analysis was obtained from 1,2-
dichloroethane. Intensity data were collected on a Rigaku
AFC-6 four-circle diffractometer with graphite monochrom-
Fig. 2 Crystal packing of compound 2b.
Table 3 Physical data of the CT complexes
˚
ated Mo-Ka radiation (l=0.71069 A) using the 2h-v scan
mode (3°<2h<52°). All collected reflections are unique.
Refined cell parameters were obtained from the setting angles
of 15 reflections with 2hÁ22°. Intensities were corrected for
Lp effects and theoretical absorption corrections. A total of
Donor, D
Acceptor, A
D5Aa
n
CN/cm−1
srtb/S cm−1
1a
1a
1b
1b
1a
TCNQ
DDQ
TCNQ
DDQ
1.151
351
2182
2.24×10−8
<10−8
1.151
251
2181
1.60×10−3
3
025 reflections were collected, 2157 reflections with I>2s(I)
<10−8
were considered as observed. The structure was solved by
direct methods and refined using SHELXL software (Siemens
SHELXL PLUS, PC version).14 All non-H atoms were refined
anisotropically using full-matrix least squares refinement based
on F2 with weights of the form given in eqn. (1).
CuCl
151
4.3×10−3
2
aDetermined based on elemental analysis. bRoom-temperature
conductivity measured on a compressed pellet.
N(1s) BE in the molecular donor is 399.21 eV, but in the salt
it is shifted to 399.87 eV. This may be due to the coordination
effect between the nitrogen atom of the donor molecule and
w=1/[s2(F 2)+(0.1426P)2+0.0000P]
o
where P=(F 2+2F 2)/3
(1)
o
c
the copper atom of CuCl .
Hydrogen atoms are included and all H-atom parameters
2
Attempts to obtain single crystals of the CT complexes
refined. Convergence to R=0.0646 (R =0.1956) was obtained
w
mentioned above are still under way. The preparation of CT
complexes of these new electron donors with other acceptors
using 219 variable parameters. The final value of S is 1.004.
Crystal data: C H NS ; crystal system: orthorhombic, space
1
5 9
8
group: Pbca; cell parameters: a=11.448(5), b=35.680(10),
˚
Table 4 Binding energies (eV) of Cu(2p ), Cl(2p ), N(1s) and
c=8.632(3) A; Z=8; Dcalcd=1.732 g cm−3; F(000)=1872.
3
/2
3/2
S(2p ) of 1a, CT complex 1a·CuCl and CuCl
/2
3
2
2
Synthesis
Compound
Cu(2p
)
Cl(2p
)
N(1s)
S(2p
)
3
/2
3/2
3/2
163.96
General. Melting points were measured with an XT –100
microscope apparatus and are uncorrected. 1H-NMR spectra
4
X
1
1
a
399.21
399.87
a·CuCl
934.38,
32.51
934.3
198.95,
197.62
199.5
166.17 (8%),
163.90 (92%)
2
9
†
CCDC reference number 1145/150. See http://www.rsc.org/
suppdata/jm/1999/1245/for crystallographic files in .cif format.
CuCl
2
J. Mater. Chem., 1999, 9, 1245–1249
1247

were recorded on a UNITY 200 (Varian) instrument. Infrared
spectra were recorded on a Perkin-Elmer SYSTEM 2000 FT-
IR spectrometer. Mass spectra were determined with the
instruments AEI-MS50 for EI-MS, KYKY-ZH-P-5 for FAB-
MS and BEFLEX III for TOF-MS. Elemental analyses were
performed on a Carlo-Erba-1106 instrument. Cyclic voltam-
metric measurements were conducted on an EGDG PAR
4,5-Ethylenedithio-4∞,5∞-(4-pyridylethylenedithio)tetra-
thiafulvalene 1a‡
Compound 4a (0.57 g, 2 mmol) and 4,5-ethylenedithio-1,3-
dithiole-2-thione (1.34 g, 6 mmol) were suspended in triisopro-
pyl phosphite (30 ml). The mixture was heated up to
1
2
20–130 °C under nitrogen atmosphere and stirred for a further
h. The resulting mixture was allowed to cool to room
3
70 System.
temperature and methanol (50 ml) was added. The mixture
was further cooled in a refrigerator. A yellow solid precipitated
out which was filtered off, washed with methanol, then recrys-
tallized from 1,2-dichloroethane to give 1a as a yellow solid
Chemicals. The (C S ) oligomer was synthesized by the
3
5 x
method described in ref. 8. Triisopropyl phosphite (Acros
Chemicals) was used without purification. All solvents were
dried by standard procedures.
(
0.24 g, 26% yield). Mp 187–188 °C (dec). Anal. calcd for
C H NS : C, 39.01; H, 2.40; N, 3.03. Found: C, 38.71; H,
1
5 11
8
2
.32; N, 2.95%. m/z (FAB) 461 (M+); d (CDCl ): 3.30 (4H,
H
3
s), 3.42 (2H, d, J 6.7), 4.64 (1H, dd), 7.32 (2H, d, J 5.0), 8.62
(
2H, d, J 5.0); nmax(KBr)/cm−1: 2914, 1597, 1443 and 1023.
4
,5-(4-Pyridylethylenedithio)-1,3-dithiole-2-thione 3a
4
,5-Ethylenedithio-4∞,5∞-(2-pyridylethylenedithio)tetra-
4
-Vinylpyridine (1.05 ml, 10 mmol) was added to a stirred
thiafulvalene 1b
suspension of oligomeric 4,5-dihydro-1,3-dithiole-2,4,5-tri-
thione (1.7 g) in dioxane (15 ml). The mixture was heated to
7
mixture was filtered hot, and the remaining solid was further
washed with CH Cl (3×10 ml) for complete extraction of
the product. The filtrate and washings were treated with
activated charcoal. The solvent was evaporated under vacuum
on a rotary evaporator. The resulting solid was recrystallized
from acetonitrile–dichloromethane (351) to give 3a as yellow
crystals (0.4 g) in 15% yield, mp 129–131 °C (dec). Anal. calcd
for C H NS : C, 39.84; H, 2.34; N, 4.64. Found: C, 39.71;
1
b was synthesized by a similar method to 1a and isolated as
5 °C and stirred for 1.5 h at this temperature. The resulting
a yellow solid in 25% yield. Mp 173–175 °C (dec). Anal. calcd
for C H NS : C, 39.01; H, 2.40; N, 3.03. Found: C, 38.49;
1
5 11
8
H, 2.16; N, 2.80%. m/z (TOF) 461 (M+); d (DMSO-d ): 3.38
2
2
H
6
(
4H, s), 3.75 (2H, m), 5.00 (1H, dd), 7.35–8.58 (4H, m);
n
max(KBr)/cm−1: 1584, 1505, 1468, 1056 and 848.
4
,5-Ethylenedithio-4∞,5∞-(4-pyridylethenylenedithio)tetra-
thiafulvalene 2a
1
0 7
5
A solution of DDQ (80 mg, 0.35 mmol) in xylene (isomer
mixture) (5 ml) was added dropwise under argon over 20 min
to a solution of 1a (92 mg, 0.2 mmol) in mixed xylenes (20 ml)
under reflux. After an additional 10 min, the reaction mixture
was allowed to cool to room temperature, then filtered and
the remaining solid was washed with CH Cl . Evaporation of
solvents from the filtrate and washing afforded an oily brown
residue, which was chromatographed on silica gel with dich-
loromethane–ethyl acetate (151) as the eluent. The product
was further purified by recrystallization from 1,2-dichloro-
ethane to give 2a as an orange solid (18 mg, 20% yield). Mp
222–224 °C (dec). Anal. calcd for C H NS : C, 39.19; H,
H, 2.06; N, 4.36%. m/z (FAB) 302 (M++1); d (CDCl ): 3.54
H
3
(
2H, d, J 3.3), 4.74 (1H, dd), 7.34 (2H, d, J 5.6), 8.67 (2H,
d, J 5.6); nmax(KBr)/cm−1: 1595, 1559, 1488 and 1064.
4
,5-(2-Pyridylethylenedithio)-1,3-dithiole-2-thione 3b
2 2
Thione 3b was prepared from 2-vinylpyridine by an analogous
procedure to that used for the synthesis of compound 3a and
isolated as yellow crystals in 20% yield, mp 122–124 °C. Anal.
calcd for C H NS : C, 39.84; H, 2.34; N, 4.64. Found: C,
1
0 7
5
3
3
9.59; H, 2.16; N, 4.48%. m/z (EI) 301 (M+); d (CDCl ):
H
3
15 9
8
.60–3.95 (2H, m), 4.95 (1H, dd), 7.28–8.60 (4H, m);
1.97; N, 3.05. Found: C, 38.76; H, 1.72; N, 2.82%. m/z (EI)
459 (M+); d (CDCl ): 3.34 (4H, s), 6.95 (1H, s), 7.43 (2H,
n
max(KBr)/cm−1: 1582, 1567, 1486, 1469, 1431 and 1058.
H
3
d, J 6.2), 8.64 (2H, d, J 6.2); n (KBr)/cm−1: 2919, 1587,
max
1
408 and 803.
4
,5-(4-Pyridylethylenedithio)-1,3-dithiol-2-one 4a
4
,5-Ethylenedithio-4∞,5∞-(2-pyridylethenylenedithio)tetra-
To a solution of thione 3a (0.5 g, 1.66 mmol) in CHCl
thiafulvalene 2b
3
(
25 ml), Hg(AcO) (1.5 g, 4.8 mmol) was added. The resulting
2
solution was stirred at room temperature for 1 h. The precipi-
tate was filtered off and the filtrate washed with water
2b was synthesized by a similar procedure to that for
compound 2a and isolated as an orange solid in 44% yield,
mp 204–206 °C (dec). Anal. calcd for C H NS : C, 39.19; H,
(
3×10 ml). After drying (Na SO ) the solvent was evaporated
2
4
15 9
8
and the resulting solid was recrystallized from acetonitrile to
give 4a as white crystals (0.39 g, 83% yield), mp 132–133 °C.
Anal. calcd for C H NOS : C, 42.08; H, 2.47; N, 4.91. Found:
1.97; N, 3.05. Found: C, 38.91; H, 1.97; N, 2.88%. m/z (EI)
459 (M+); d (CDCl ): 3.32 (4H, s), 7.34 (1H, s), 7.60–8.60
H
3
(4H, m); n (KBr)/cm−1: 2922, 1623, 1581, 1460, 1434, 1022
1
0 7
4
max
C, 42.09, H, 2.22; N, 4.65%. m/z (FAB) 286 (M++1);
and 761.
d (CDCl ): 3.56 (2H, d, J 11.4), 4.74 (1H, dd), 7.34 (2H, d,
H
3
J 6.0), 8.67 (2H, d, J 6.0); nmax(KBr)/cm−1: 1671, 1625, 1597
Preparation of CT complexes
and 1504.
To a solution of the donor (1 equiv.) in dichloromethane
under reflux, a hot solution of TCNQ or DDQ (1 equiv.) in
acetonitrile was added. The mixture was heated gently under
reflux for 30 min before cooling. After several hours the charge
transfer complexes were collected by filtration.
4
,5-(2-Pyridylethylenedithio)-1,3-dithiol-2-one 4b
Compound 4b was prepared from thione 3b by an analogous
procedure to that used for the synthesis of compound 4a and
isolated as white crystals in 80% yield, mp 102–104 °C. Anal.
calcd for C H NOS : C, 42.08; H, 2.47; N, 4.91. Found: C,
4
3
1
a with TCNQ: mp >300 °C. n (KBr)/cm−1: 3419, 2182,
max
2
123, 1733, 1690, 1631, 1571, 1505, 1414, 1346, 1282, 1179,
1
0 7
4
2.07, H, 2.19; N, 4.72%. m/z (EI) 285 (M+); d (CDCl ):
‡
IUPAC name: 5,5∞,6,6∞-tetrahydro-5-(4-pyridyl)-2,2∞-bi([1,3]dithi-
H
3
.60–4.95 (2H, m), 4.95 (1H, dd), 7.30–8.60 (4H, m);
olo[4,5-b][1,4]dithiin-2-ylidene). Related compounds 2–4 can be
named similarly.
n
max(KBr)/cm−1: 1678, 1615, 1585, 1501, 1469, 1142 and 901.
1
248
J. Mater. Chem., 1999, 9, 1245–1249

1
C
107. C, 47.92; H, 2.37; N, 10.68 (Anal. calcd for
: C, 48.07; H, 2.43; N, 10.22%).
valuable discussions. The present work was supported financi-
ally by the Chinese Academy of Sciences (KJ951-A1–501–03).
H
N S
2
8.5 16.1 5.1 8.8
1
a with DDQ: mp >300 °C. n (KBr)/cm−1: 3417, 3025,
max
2
214, 1629, 1590, 1455, 1410, 1255, 1201, 1171, 1035. The
References
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1
F. Wudl, D. Wobschall and E. J. Hufnagel, J. Am. Chem. Soc.,
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2
2
N, 4.34%).
1
b with TCNQ: mp >300 °C. n (KBr)/cm−1: 4324, 2924,
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2
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.1
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8.5 16.1 5.1 8.8
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1
b
n
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4
5
6
3
022, 2220, 1622, 1579, 1444, 1348, 1170, 1107. The composi-
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1
4
b ·DDQ·(CH CN)
1.5
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2
3
7
41 26.5 2 5.5 2 16
C, 40.63; H, 2.20; N, 6.36%).
8
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1
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2
2
9
0
(
5 ml) was added to a hot solution of 1a (46 mg, 0.1 mmol)
1
in dichloromethane (5 ml). The resulting mixture was stirred
overnight at room temperature. The precipitate was collected
by filtration; 1a·CuCl was obtained as a black solid after
drying under vacuum. Mp >300 °C. Anal. calcd for
C H Cl NS Cu: C, 30.22; H, 1.86; N, 2.35. Found: C, 29.71;
H, 1.66; N, 1.97%.
1
1
11 H. Kobayashi, A. Kobayashi, Y. Sasaki, G. Saito and
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Acknowledgements
1
4
G. M. Sheldrick, SHELXL-93, Program for Crystal Structure
Refinement, University of G o¨ ttingen, Germany, 1993.
We thank Professor Zhesheng Ma and Mrs Ming Xiong of
the China University of Geosciences for their X-ray crystallog-
raphy analysis and Associate Professor Bing Zhang for
Paper 9/00063A
J. Mater. Chem., 1999, 9, 1245–1249
1249