Molecular modifications of methylenedithio-tetraselenafulvalene (MDT-TSF) and methylenedithio-diselenadithiafulvalene (MDT-ST) for superior electron donors

Article abstract of DOI:10.1055/s-2004-822362

The dimethyl-, bis(methylthio)-, and ethylenedithio-derivatives of methylenedithio-tetraselenafulvalene and methylenedithio-diselenadithiafulvalene have been synthesized as new electron donors. The formation and electrical conductivities of their radical

Full text of DOI:10.1055/s-2004-822362

PAPER
1315
Molecular Modifications of Methylenedithio-Tetraselenafulvalene
(MDT-TSF) and Methylenedithio-Diselenadithiafulvalene (MDT-ST) for
Superior Electron Donors
M
olecular Modific
a
ation of
M
D
z
T–TSF an
u
d
M
DT–ST o Takimiya,* Yoshiro Kataoka, Yuki Nakamura, Yoshio Aso, Tetsuo Otsubo
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8527,
Japan
Fax +81(82)4248527; E-mail: ktakimi@hiroshima-u.ac.jp
Received 6 April 2004
This paper is dedicated to Emeritus Professor T. Mukaiyama on the occasion of his 77th birthday
H3C
CH3
Se
Se
Se
Se
Abstract: The dimethyl-, bis(methylthio)-, and ethylenedithio-de-
rivatives of methylenedithio-tetraselenafulvalene and methylene-
dithio-diselenadithiafulvalene have been synthesized as new
electron donors. The formation and electrical conductivities of their
radical cation salts are examined.
X
X
Se
Se
S
S
H3C
S
CH3
S
TMTSF
S
S
X = Se: MDT-TSF
X = S: MDT-ST
Keywords: tetraselenafulvalenes, selenium, electron donors, or-
ganic conductors, crystal structure
S
S
S
S
BEDT-TTF
1a: R = Me, X = Se
1b: R = SMe, X = Se
1c: R = Me, X = S
1d: R = SMe, X = S
1e: R,R = S(CH2)2S, X = S
R
R
X
X
Se
Se
S
S
Methylenedithio-tetraselenafulvalene (MDT-TSF), [5H-
2-(1,3-diselenol-2-ylidene)-1,3-diselena-4,6-dithiapent-
alene], is a prototypical electron donor capable of produc-
ing superconducting radical cation salts with various
Figure 1
–
– 1
linear anions such as AuI2 and I3 . The related diselena-
dithiafulvalene donor (MDT-ST), [5H-2-(1,3-dithiol-2-
ylidene)-1,3-diselena-4,6-dithiapentalene], also gives su-
perconducting radical cation salts isostructural with the
MDT-TSF salts.2 Among molecular-based superconduc-
tors, these are quite unique not only in their relatively high
Tc (up to 5.5 K) but also in their unusual structures char-
acteristic of uniform donor stacks and an anion lattice in-
commensurate with the donor lattice, resulting in a non-
integral donor/anion ratio of 1:0.42–0.44.3 Our special in-
terest in developing new electron donors has focused on
the hybrids between MDT-TSF or MDT-ST and other
superior electron donors, such as bis(ethylene-
dithio)tetrathiafulvalene (BEDT-TTF) and tetramethyltet-
raselenafulvalene (TMTSF), forming a number of
superconducting radical cation salts.4 In this paper, we re-
port the synthesis and electrochemical properties of the
dimethyl-, bis(methylthio)-, and ethylenedithio-substitut-
ed derivatives of MDT-TSF and MDT-ST (1a–e,
Figure 1), together with the formation and eletrical con-
ductivities of their charge-transfer radical cation salts.
the cross-coupling reactions are largely dependent on the
combinations of the two reactants. The syntheses of the
dimethyl and bis(methylthio) derivatives (4a and 4b) of
tetraselenafulvalene were accomplished in 42% and 35%
yields, respectively, by treatment of the corresponding
1,3-diselenole-2-selone (2a6 or 2b7) with 3a. Similarly,
the dimethyl derivative (4c) of diselenadithiafulvalene
was obtained in 29% yield by treatment of 4,5-dimethyl-
1,3-dithiole-2-selone (2c)8 with 3a. Improvement of the
low yields for the cross-coupling reactions was attempted.
However, the cross-coupling reaction of 4,5-dimethyl-
1,3-dithiole-2-thione9 and 3b gave only a trace amount of
4c. On the other hand, the other diselenadithiafulvalene
derivatives (4d and 4e) were obtained by a combination of
the corresponding 1,3-dithiole-2-thione (2d or 2e)10 and
the 1,3-diselenol-2-one (3b, Z = O) in 78% and 73%
yields, respectively. In the second step, the thus obtained
4a–e were subjected to the deprotection of 2-methoxycar-
bonylethylthio group with cesium hydroxide in DMF so-
lution to produce the TSF- and STF-thiolate anion
intermediate (4¢), which, on in situ treatment with bromo-
chloromethane, smoothly gave the corresponding 2-meth-
ylthio-3-chloromethylthio-TSF and -STF derivatives (5a–
c) in 52–87% yields.11 Finally, the ring-closing reaction
via transalkylation on the sulfur atom was initiated by
treatment with sodium iodide to afford the MDT-TSF and
MDT-ST derivatives (1a–e) in 37–66% yields. All these
new compounds are well characterized by spectroscopic
measurements as well as combustion elemental analyses.
The synthesis of new donors (1a–e) is outlined in
Scheme 1. The first of this three-step route is trimethyl
phosphite-mediated cross-coupling reactions between
1,3-dichalcogenole-2-chalcogenones (2a–e) and 4-meth-
ylthio-5-(2-methoxycarbonylethylthio)-1,3-diselenole-2-
selone (3a)5 or 1,3-diselenol-2-one (3b).2 The yields of
SYNTHESIS 2004, No. 9, pp 1315–1320
x
x
.
x
x
.2
0
0
4
Advanced online publication: 12.05.2004
DOI: 10.1055/s-2004-822362; Art ID: C01704SS
© Georg Thieme Verlag Stuttgart · New York
The electrochemical properties of new donors (1a–e)
were investigated by means of cyclic voltammetry, and

1316
K. Takimiya et al.
PAPER
SMe
S
SMe
S
R
R
R
R
X
X
Se
Se
Se
Se
P(OMe)3
X
X
Z
Y
+
CO2Me
CO2Me
2a: R = Me, X = Y = Se
4a: R = Me, X = Se
4b: R = SMe, X = Se
4c: R = Me, X = S
4d: R = SMe, X = S
2b: R = SMe, X = Y = Se
2c: R = Me, X = S, Y = Se
2d: R = SMe, X = Y = S
2e: R,R = S(CH2)2S, X = Y = S
3a: Z = Se
3b: Z = O
4e: R,R = S(CH2)2S, X = S
CsOH·H2O
R
SMe
SMe
Se
R
R
BrCH2Cl
X
Se
Se
X
X
NaI
X
R
Se
S-
SCH2Cl
5a: R = Me, X = Se
5b: R = SMe, X = Se
5c: R = Me, X = S
4'
5d: R = SMe, X = S
5e: R,R = S(CH2)2S, X = S
Me
1a: R = Me, X = Se
1b: R = SMe, X = Se
1c: R = Me, X = S
1d: R = SMe, X = S
1e: R,R = S(CH2)2S, X = S
-MeI
R
R
R
X
X
Se
Se
S
S
X
X
Se
Se
S
I-
S
R
5'
Scheme 1 Synthesis of derivatives of MDT-TSF and MDT-ST (1a–e)
Table 1 Half-Wave Oxidation Potentialsa of Electron Donors (1a–
1e)
their half-wave oxidation potentials are summarized in
Table 1. All molecules showed two reversible redox cou-
ples corresponding to the consecutive formation of radical
cation and dication species, as usually seen for tetrachal-
cogenafulvalenes. When compared to those of the parent
MDT-TSF and MDT-ST, the oxidation potentials of the
derivatives synthesized here are somewhat lowered by
their electron-donating methyl groups and elevated by
electron-withdrawing alkylthio groups, but the first oxida-
tion potentials (+0.44–0.61 V vs. Ag/AgCl in PhCN) are
still low and roughly comparable with those of TMTSF
(+0.45 V) and BEDT-TTF (+0.52 V). That is, they are ex-
pected to behave as good electron donors. In a detailed
comparison, the MDT-ST derivatives 1c–e show lower
oxidation potentials than the corresponding MDT-TSF
derivatives 1a and 1b indicating stronger electron donat-
ing abilities for the former.
Donor
E11/2 (V)
0.55
E21/2 (V)
0.82
DE (V)
0.27
0.21
0.28
0.20
0.22
0.23
0.28
1a
1b
0.61
0.82
1c
0.44
0.72
1d
0.56
0.76
1e
0.55
0.77
MDT-TSFb
MDT-STc
0.56
0.83
0.50
0.78
a Vs. Ag/AgCl electrode in PhCN containing 0.1 M n-Bu4ClO4 as
supporting electrolyte. Pt working and counter electrodes, scan rate
100 mV/s, 23 °C.
b Ref.5
Electrochemical crystallization experiments using these
donors were carried out, and four radical cation salts of
good crystalline shapes were obtained from the donor 1a
and one from 1e, as listed in Table 2. The electrical con-
ductivities of these radical cation salts measured at room
temperature were highly varied in the range of 100–103 S
cm–1. Most of them showed semi-conducting behavior in
the variable temperature conductivity measurements, but
the variable temperature conductivities of the ClO4 salt of
1a showing an extraordinarily high room temperature
conductivity of 1500 S cm–1 could not be measured, be-
cause the crystal was fragile under cooling. Only the crys-
tals of the PF6 salt of 1a showed metallic behavior down
to ca. 130 K, and its crystal structure was elucidated by X-
ray crystallographic analysis. The crystal contains three
crystallographically independent donor molecules (donor
A, B, and C), one PF6 anion, and one chlorobenzene mol-
c Ref.2
ecule as the solvent of crystallization, resulting in the
composition of (1a)3(PF6)(PhCl). All the donor mole-
cules, A, B, and C are almost planar, and their C=C bond
lengths between two 1,3-diselenole rings are in the range
of 1.34–1.36 Å, indicating almost equal charge distribu-
tion on each donor molecule. As shown in Figure 2a, the
crystal structure involves the alternative packing of the
conducting donor layers and the insulating anion layers
containing chlorobenzene molecules. The donor layer is
comprised of stacking tetramers (A-B-B¢-A¢) and dimers
(C-C¢), which are closely embedded with the interrelation
of ‘face-to-edge’ mode (Figure 2b). Such face-to-edge
structures are common for conventional k-type conduc-
Synthesis 2004, No. 9, 1315–1320 © Thieme Stuttgart · New York

PAPER
Molecular Modification of MDT–TSF and MDT–ST
1317
Table 2 Radical Cation Salts of 1a and 1e
Donor Anion Appearance
sr.t./S cm–1a Remarks
1a
1a
1a
1a
1e
I2Br–
ClO4
AsF6
black needles 73
semi-conductive
–
–
b
black needles 1500
-
black plates
black plates
black plates
1.4
38
semi-conductive
metallic up to 130 K
semi-conductive
–
PF6
–
AsF6
9.4
a Measured on a single crystal with a standard four probe method.
b Crystals were too fragile to measure the conductivity under cooling.
tors, in which the dimeric donor pairs are packed in ‘face-
to-edge’ manner, but the case with the stacking tetramer
structure is very rare among organic conductors.12
In conclusion, we have successfully synthesized the di-
methyl-, bis(methylthio)-, and bis(ethylenedithio)-deriva-
tives of MDT-TSF and MDT-ST using a three-step
synthetic route consisting of cross-coupling, deprotec-
tion-realkylation, and hetrocyclization on the sulfur atom.
All the new compounds have good electron-donating abil-
ities, and upon electrocrystallization, the dimethyl deriva-
tive of MDT-TSF 1a and the ethylenedithio derivative of
MDT-ST 1e gave conducting radical cation salts of good
crystalline shapes. Among them, the ClO4 salt of 1a
showed an extraordinarily high room temperature con-
ductivity of 1500 S cm–1. The PF6 salt of 1a showed me-
tallic behavior down to ca. 130 K, and its crystal structural
analysis revealed a unique donor arrangement consisting
of the stacking tetramers and dimers in the ‘face-to-edge’
interrelation manner. These results indicate that the mo-
lecular modifications of MDT-TSF and MDT-ST can of-
fer promising electron donors for new intriguing
conducting radical cation salts. It should be noticed that in
the present synthesis, the key intermediates 4a–e can be
utilized for the synthesis of homologous electron donors
with different fused rings, such as ethylenedithio- and
propylenedithio-rings, on the 1,3-diselenole moiety, pro-
vided that the thiolate anion intermediate 4¢ is alkylated
with an appropriate chlorobromoalkane reagent.5 Further
study along this direction is now under way.
Figure 2 Crystal structure of (1a)3(PF6)(PhCl): (a) a-axis projection
(top); (b) donor arrangement in the conducting donor layer (bottom)
roshima University. Cyclic voltammetry (CV) was carried out on a
Hokuto Denko HA-301 potentiostat equipped with a Hokuto Denko
HB-104 function generator using benzonitrile as solvent containing
tetrabutylammonium perchlorate (n-Bu4NClO4, 0.1 M) as support-
ing electrolyte with a sweep rate of 100 mV/s. Counter and working
electrodes were made of Pt, and the reference electrode was Ag/
AgCl.
Phosphite-Mediated Cross-Coupling Reaction of 4-Methylthio-
5-(2-methoxycarbonylethylthio)-1,3-diselenole-2-chalcogenone
(3) and 1,3-Dichalcogenole-2-chalcogenones (2); General Proce-
dure: 2,3-Dimethyl-6-methylthio-7-(2-methoxycarbonylethyl-
thio)-tetraselenafulvalene (4a) as an Example
To a refluxing mixture of 4,5-dimethyl-1,3-diselenole-2-selone (2a,
303 mg, 1 mmol) and 4-methylthio-5-(2-methoxycarbonylethyl-
thio)-1,3-diselenole-2-selone (3a, 1.36 g, 3.1 mmol) in benzene (40
mL) was added trimethyl phosphite (2.4 mL, 5 mmol). After the re-
sulting mixture was refluxed for 3 h, the solvent and the excess
phosphite reagent were evaporated off, and the residue was purified
by column chromatography (silica gel, CH2Cl2): the first less-polar
fraction (Rf = 0.9) consisted of tetramethyltetraselenafulvalene
(TMTSF, 62 mg, 28%), and the last fraction (Rf = 0.3) gave 2,6(7¢)-
bis(methylthio)-3,7(6¢)-bis(2-methoxycarbonylethylthio)-tetrasel-
enafulvalene (643 mg, 58%). The middle fraction was again sub-
jected to column chromatography (silica gel, CH2Cl2–hexane, 1:1),
and the main fraction (Rf = 0.4–0.5, CH2Cl2–hexane, 1:1) gave the
desired cross-coupling product, 2,3-dimethyl-6-methylthio-7-(2-
methoxycarbonylethylthio)-tetraselenafulvalene (4a). Yield: 242
mg (42%); red solid; mp 103–104 °C.
All chemicals and solvents are of reagent grade. All reactions were
carried out under a nitrogen atmosphere with anhyd solvents. Col-
umn chromatography was carried out with Daisogel IR-60 (63–210
mm). Melting points are uncorrected. NMR spectra were obtained in
CDCl3 with a JEOL Lambda 400 spectrometer operating at 400
MHz for 1H and 100 MHz for 13C with TMS as internal reference;
chemical shifts (d) are reported in ppm. EI–MS spectra were ob-
tained on a Shimadzu QP-2000 or a Shimadzu QP-5050A spectro-
meter using an electron impact ionization procedure (70 eV). The
molecular ion peaks of the selenium-containing compounds showed
a typical selenium isotropic pattern, and all the selenium-containing
mass peaks are reported for 80Se. IR spectra were obtained on a Shi-
madzu FTIR-8100A spectrometer. Elemental analyses were per-
formed by Mr. Hideaki Iwatani, Microanalytical Laboratory in
Department of Applied Chemistry, Faculty of Engineering, Hi-
Synthesis 2004, No. 9, 1315–1320 © Thieme Stuttgart · New York

1318
K. Takimiya et al.
PAPER
2-Methylthio-3-chloromethylthio-tetraselenafulvalenes or 2-
IR (KBr): 1732 cm–1 (C=O).
Methylthio-3-chloromethylthio-diselenadithiafulvalenes (5);
General Procedure; 2-Methylthio-3-chloromethylthio-6,7-di-
methyltetraselenafulvalene (5a) as an Example
1H NMR (CDCl3): d = 1.99 (s, 6 H), 2.45 (s, 3 H), 2.69 (t, J = 7.3
Hz, 2 H), 3.07 (t, J = 7.3 Hz, 2 H), 3.70 (s, 3 H).
13C NMR (CDCl3): d = 16.57, 21.02, 32.48, 34.97, 52.35, 102.14,
109.87, 126.48, 127.51, 127.62, 136.34, 172.32.
To a degassed DMF solution (20 mL) of 4a (17 mg, 0.34 mmol) was
added CsOH·H2O (57 mg, 0.34 mmol) in MeOH (5 mL) during 5
min with stirring at r.t. After the mixture was stirred for further 0.5
h, excess bromochloromethane (ca. 1 mL) was added, and the mix-
ture was stirred for 2 h. The reaction mixture was diluted with water
(100 mL) and extracted with CH2Cl2 (4 × 20 mL). The extract was
washed with water (100 mL), dried over Na2SO4, and concentrated.
The resulting crude product was purified by column chromatogra-
phy on silica gel eluted with CH2Cl2–hexane (1:1) to give 2-meth-
ylthio-3-chloromethylthio-6,7-dimethyltetraselenafulvalene (5a)
(Rf = 0.6). Recrystallization from CH2Cl2–hexane (1:1) gave an an-
alytically pure sample. Yield: 158 mg (85%); orange solid; mp 139–
140 °C.
MS (EI): m/z = 586 [M+].
Anal. Calcd for C13H16O4S2Se4: C, 26.73; H, 2.76. Found: C, 26.76;
H, 2.75.
2,3,6-Tris(methylthio)-7-(2-methoxycarbonylethylthio)-tetra-
selenafulvalene (4b) from 2b and 3a
Yield: 35%; dark yellow oil.
IR (neat): 1736 cm–1 (C=O).
1H NMR (CDCl3): d = 2.46 (s, 6 H), 2.47 (s, 3 H), 2.70 (t, J = 7.3
Hz, 2 H), 3.07 (t, J = 7.3 Hz, 2 H), 3.71 (s, 3 H).
13C NMR (CDCl3): d = 20.46 (2 ×), 20.52, 31.96, 34.35, 51.82,
107.20, 107.44, 125.76, 130.14, 130.44, 136.68, 171.58.
MS (EI): m/z = 648 [M+].
1H NMR (CDCl3): d = 2.00 (s, 6 H, CH3), 2.48 (s, 3 H, CH3), 4.82
(s, 2 H, CH2).
13C NMR (CDCl3): d = 16.09, 20.83, 30.88, 50.95, 101.50, 110.28,
123.68, 127.03, 127.18, 138.13.
Anal. Calcd for C13H16O2S4Se4: C, 24.08; H, 2.49. Found: C, 23.94;
H, 2.45.
MS (EI): m/z = 548 [M+].
Anal. Calcd for C10H11S2ClSe4: C, 21.97; H, 2.03. Found: C, 22.06;
H, 1.93.
6,7-Dimethyl-2-methylthio-3-(2-methoxycarbonylethylthio)-
diselenadithiafulvalene (4c) from 2c and 3a
Yield: 29%; reddish brown microcrystals (CH2Cl2–MeOH); mp
102–103 °C.
2-Chloromethylthio-3,6,7-tris(methylthio)-tetraselenaful-
valene (5b)
Yield: 57%; red needles [CH2Cl2–hexane (1:1)]; mp 94–95 °C.
1H NMR (CDCl3): d = 2.462 (s, 3 H), 2.464 (s, 3 H), 2.48 (s, 3 H),
4.83 (s, 2 H).
13C NMR (CDCl3): d = 20.54 (2 ×), 20.85, 50.97, 107.11, 108.28,
123.44, 130.21, 130.63, 137.99.
MS (EI): m/z = 610 [M+].
IR (KBr): 1732 cm–1 (C=O).
1H NMR (CDCl3): d = 1.94 (s, 6 H), 2.46 (s, 3 H), 2.69 (t, J = 7.2
Hz, 2 H), 3.06 (t, J = 7.2 Hz, 2 H), 3.71 (s, 3 H).
13C NMR (CDCl3): d = 20.52, 31.92, 34.45, 51.83, 92.64, 121.63,
123.16, 123.28, 125.19, 135.17, 173.73.
MS (EI): m/z = 490 [M+].
Anal. Calcd for C10H11S4ClSe4: C, 19.67; H, 1.82. Found: C, 19.68;
H, 1.76.
Anal. Calcd for C13H16O2S4Se2: C, 31.84; H, 3.29. Found: C, 31.89;
H, 3.26.
2-Methylthio-3-chloromethylthio-6,7-dimethyl-diselenadithia-
fulvalene (5c)
Yield: 87%; red crystals [CH2Cl2–hexane (1:1)]; mp 135–136 °C.
1H NMR (CDCl3): d = 1.94 (s, 6 H), 2.47 (s, 3 H), 4.82 (s, 2 H).
13C NMR (CDCl3): d = 13.79 (2 ×), 20.83, 50.96, 92.49, 122.48,
12.03, 123.20, 123.36, 137.81.
MS (EI): m/z = 452 [M+].
2,3,6-Tris(methylthio)-7-(2-methoxycarbonylethylthio)-disel-
enadithiafulvalene (4d) from 2d and 3b
Yield: 78%; dark yellow oil.
IR (neat): 1738 cm–1 (C=O).
1H NMR (CDCl3): d = 2.36 (s, 6 H), 2.40 (s, 3 H), 2.63 (t, J = 7.3
Hz, 2 H), 3.00 (t, J = 7.3 Hz, 2 H), 3.64 (s, 3 H).
13C NMR (CDCl3): d = 19.02 (2 ×), 20.35, 31.73, 34.15, 51.63,
98.99, 118.313, 124.86, 127.36, 127.63, 134.90, 171.32.
MS (EI): m/z = 556 [M+].
Anal. Calcd for C10H11ClS4Se2: C, 26.52; H, 2.45. Found: C, 26.61;
H, 2.46.
Anal. Calcd for C13H16O2S6Se2: C, 28.15; H, 2.91. Found: C, 28.10;
H, 2.80.
2,3,6-Tris(methylthio)-7-chloromethylthio-diselenadithiaful-
valene (5d)
Yield: 52%; red powder [CH2Cl2–hexane (1:1)]; mp 101–102 °C.
1H NMR (CDCl3): d = 2.43 (s, 6 H), 2.48 (s, 3 H), 4.83 (s, 2 H).
13C NMR (CDCl3): d = 19.24 (2 ×), 20.82, 50.12, 99.00, 119.23,
122.95, 127.73, 128.10, 137.47.
6,7-Ethylenedithio-2-methylthio-3-(2-methoxycarbonylethyl-
thio)-diselenadithiafulvalene (4e) from 2e and 3b
Yield: 73%; red oil.
IR (neat): 1732 (C=O), 1049 cm–1 (C–O–C).
1H NMR (CDCl3): d = 2.46 (s, 3 H), 2.69 (t, J = 7.2 Hz, 2 H), 3.27
(t, J = 7.2 Hz, 2 H), 3.06 (s, 4 H), 3.71 (s, 3 H).
13C NMR (CDCl3): d = 20.49, 30.12 (2 ×), 31.91, 34.29, 51.77,
102.56, 113.86, 113.99, 116.54, 125.00, 135.03, 171.50.
MS (EI): m/z = 544 [M+].
MS (EI): m/z = 516 [M+].
Anal. Calcd for C10H11ClS6Se4: C, 23.23; H, 2.14. Found: C, 23.10;
H, 2.17.
6,7-Ethylenedithio-2-methylthio-3-chloromethylthio-diselena-
dithiafulvalene (5e)
Yield: 61%; orange fine needles [CH2Cl2–hexane (1:1)]; mp 127–
128 °C.
Anal. Calcd for C13H14O2S6Se2: C, 28.26; H, 2.55. Found: C, 27.88;
H, 2.20.
1H NMR (CDCl3): d = 2.47 (s, 3 H), 3.30 (s, 4 H), 4.81 (s, 2 H).
Synthesis 2004, No. 9, 1315–1320 © Thieme Stuttgart · New York

PAPER
Molecular Modification of MDT–TSF and MDT–ST
1319
13C NMR (CDCl3): d = 20.86, 30.20 (2 ×), 50.90, 102.56, 114.01,
Preparation of Conducting Radical Cation Salts
114.17, 117.35, 122.95, 137.39.
Crystals of radical cation salts summarized in Table 2 were pre-
pared by an electrochemical crystallization method using a two-
compartment H-shaped glass cell equipped with a platinum wire as
the electrodes. A typical procedure is as follows; donor molecule (3
MS (EI): m/z = 514 [M+].
Anal. Calcd for C10H9ClS6Se4: C, 23.32; H, 1.76. Found: C, 23.33;
H, 1.77.
–
–
mg) and tetrabutylammonium salts [(n-Bu4N)X, X = ClO4 , PF6 ,
–
AsF6 , I2Br–, 20–100 mg] were placed in the anode and the cathode
Methylenedithio-tetraselenafulvalene and -diselenadithiaful-
valene Derivatives; Dimethyl-methylenedithio-tetraselenaful-
valene (1a); General Procedure
compartment, respectively. Chlorobenzene containing ca. 10% of
EtOH (ca. 18 mL) was added, and the resulting solution was deaer-
ated with a dry nitrogen stream. The constant current of 0.1–0.2 mA
was applied at 25 °C. Within two weeks, radical cation salts as black
plates or needles grew on the anode. The crystals were collected by
filtration, washed with CH2Cl2, dried, and utilized for the conduc-
tivity measurements.
A mixture of 5a (113 mg, 0.21 mmol) and NaI (47 mg, 0.63 mmol)
in 2-butanone (20 mL) was refluxed for 13.5 h. The mixture was di-
luted with water (60 mL), and the resulting precipitate was collected
by filtration. The solid was dissolved in carbon disulfide (50 mL)
and the solution was washed with water (2 × 30 mL), dried over
CaCl2, and then concentrated. Recrystallization of the resulting sol-
id from chlorobenzene gave 1a. Yield: 49 mg (47%); yellow nee-
dles; mp 168–170 °C.
X-Ray Crystal Structure Analysis of (1a)3PF6(PhCl)
The X-ray analysis was performed on a Rigaku AFC6S four-circle
diffractometer (CuKa radiation, l = 1.54178 Å, graphite monochro-
mator, 2qmax = 126.2°). The structure was resolved with direct meth-
ods (SHELXS-86)13 and refined by full-matrix least-squares on
|F|.14 All the non-hydrogen atoms were refined anisotropically, and
the hydrogen atoms were not included in the refinement.
1H NMR (CDCl3): d = 1.99 (s, 6 H, CH3), 4.83 (s, 2 H, CH2).
MS (EI): m/z = 498 [M+].
Anal. Calcd for C9H8S2Se4: C, 21.79; H, 1.63. Found: C, 21.54; H,
1.55.
Crystal data for (1a)3PF6(PhCl): C33H29S6Se12PF6Cl, M = 1745.89,
monoclinic space group, P21/c (No. 14), a = 8.366(3), b =
34.071(3), c = 17.213(3) Å, b = 100.70(2)°, V = 4821(2) Å3, Z = 4,
rcalcd = 2.405 g cm–3, R = 0.0613, 5362 observed reflections [I >
2.0s (I)], 533 refined parameters. Crystallographic data (excluding
structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as sup-
plementary publication no. CCDC-235172. Copies of the data can
be obtained free of charge on application to The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax: +44(1223)336033;
e-mail: deposit@chemcrys.cam.ac.uk].
Bis(methylthio)-methylenedithio-tetraselenafulvalene (1b)
Yield: 62%; brown plates [carbon disulfide–hexane (2:1)]; mp 115–
116 °C.
1H NMR (CDCl3): d = 2.45 (s, 6 H), 4.87 (s, 2 H).
13C NMR (CDCl3): d = 20.58, 44.69, 111.24, 112.06, 116.04,
130.47.
MS (EI): m/z = 562 [M+].
Anal. Calcd for C9H8S4Se4: C, 19.29; H, 1.44. Found: C, 19.33; H,
1.47.
Acknowledgment
Dimethyl-methylenedithio-diselenadithiafulvalene (1c)
Yield: 37%; dark red needles [carbon disulfide–hexane (2:1)]; mp
148–150 °C.
1H NMR (CDCl3): d = 2.45 (s, 6 H), 4.87 (s, 2 H).
13C NMR (CDCl3): d = 13.68, 45.20, 97.77, 116.06, 123.09, 123.94.
MS (EI): m/z = 402 [M+].
This work was partially supported by a Grant-in-Aid for Scientific
Research on Priority Areas of Molecular Conductors (No.
15073218) from the Ministry of Education, Culture, Sports, Sci-
ence, and Technology, Japan.
References
Anal. Calcd for C9H8S4Se2: C, 26.87; H, 2.00. Found: C, 26.73; H,
1.95.
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MS (EI): m/z = 466 [M+].
Anal. Calcd for C9H6S6Se2: C, 23.27; H, 1.30. Found: C, 23.19; H,
1.28.
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Synthesis 2004, No. 9, 1315–1320 © Thieme Stuttgart · New York

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