5906 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Yamamoto et al.
purchased from Kokusan Chem. Co. Ltd., and tetra(n-butyl)ammonium
dibromoaurate were purchased from Tokyo Chem. Industry Co. Ltd.,
TIE was purchased from Aldrich Chem. Co., and they were used
without further purification. 1,1,2-Tricholoroethane was purchased from
Wako Chem. Co. Ltd. and washed successively with concentrated H2-
SO4, water, and NaHCO3 aqueous, then dried with CaCl2, and
fractionally distilled. Standard H-shaped cells (20 mL) and platinum
electrodes (1 mm in diameter) were used for galvanostatic oxidation.
ever, the neutral component comes from the solvent used for
the crystal growth and is incorporated incidentally. The solvent
molecules tend to be packed loosely and are often disordered.
Consequently, to develop well-organized multicomponent sys-
tems, rational introduction of neutral molecules are required.
With above aspects in mind, we tried utilizing the Lewis
acid-base interaction in order to introduce neutral molecule(s)
into molecular conductors more deliberately. At the same time,
by means of this interaction, we intended to fabricate supra-
molecular assembly in the crystal to provide new structures and
properties. Although preceding research has revealed that the
functionalization of donor molecules is valid for the application
of the supramolecular chemistry to molecular conductors,11
neutral molecules have never been used in this purpose. We
think that the supramolecular chemistry of the multicomponent
molecular conductors still remains unexplored and is worth
challenge.
Recently, we succeeded to fabricate the supramolecular
assemblies with halide anions (Cl- or Br-) and DIA in BEDT-
TTF salts.12 We selected DIA, tetraiodoethylene (TIE), and
p-bis(iodoethynyl)benzene (pBIB) as key components for the
supramolecular system in this article. Electron-deficient iodine
atoms in these molecules are essential for the assembly. Lewis-
acidic iodine atoms coordinate to Lewis-basic anions to form
unique polymeric structures. The donor molecules BEDT-TTF
and EDT-TTF () ethylenedithiotetrathiafulvalene) are used for
the formation of the conduction path. These donors are at
present two of the most promising donors in the search for new
metallic or superconducting salts. Moreover, they are suitable
counterparts to examine ability of our supramolecular system
to build new structures, because the possible molecular arrange-
ments with discrete anions have already been investigated
thoroughly. Therefore, the plentiful library of preceding
investigations allows us to judge whether the formation of the
obtained donor arrangement is possible without the existence
of the supramolecular assembly or not. With this strategy, we
have studied eight conductive cation-radical salts. In these
molecular conductors, anions and iodine-containing neutral
molecules form novel supramolecular assemblies: one-dimen-
sional (1D) chains, 2D sheets, and a three-dimensional (3D)
network. In addition, the assemblies yield novel donor arrange-
ments and thus affect the physical properties of these salts.
pBIB. To a THF (200 mL) solution of p-diethynylbenzene (2.65 g,
21.0 mmol)16 was added n-butyllithium in hexane (1.56 N, 27.0 mL,
42.1 mmol) dropwise at -78 °C. After stirring at 0 °C for 2 h, iodine
(10.72 g, 42.2 mmol) in 120 mL THF was added at -78 °C. This
solution was gradually warmed to room temperature, and an aqueous
solution of sodium thiosulfate (ca. 10%, 200 mL) was added portion-
wise. The organic layer was extracted with Et2O (300 mL × 2), washed
with brine, and dried. Purification by silica gel column chromatography
with 1:1 mixture of hexane and dichloromethane as an eluent gave
crude pBIB (3.81 g, 10.1 mmol, 48.0%). Recrystallization of the crude
product from hot chloroform gave pure pBIB as pale yellow flakes.
m/z: 380; 1H NMR: 7.36 (4H, s); Calc. C: 31.45, H: 1.05, N: 0.0.
Found. C: 31.84, H: 1.19, N: 0.0; Mp 175 °C (dec).
Crystal Preparation: General. Galvanostatic oxidation procedures
of 20 mL solutions containing the donor molecules, neutral molecules,
and supporting electrolytes were performed under argon atmosphere.
Constant currents were applied for several days. Crystals with enough
quality for resistivity measurement and X-ray structure analysis
harvested on the electrodes.
X-ray Diffraction Studies. Eight crystals obtained as described
above were mounted on glass fibers using epoxy cement. X-ray
diffraction data were collected on a MAC Science automatic four-circle
diffractometer (MXC18), a Rigaku automatic four-circle diffractometer
(AFC6S), or a MAC Science imaging plate (DIP320) with graphite-
monochromated Mo KR radiation at 293 K. The intensities were
corrected for Lorentz and polarization effects. The structures were
solved by a direct method and refined by full-matrix least-squares
methods. For 5 and 8, the refinements were performed using SHELXL-
93.17 Analytical absorption correction was carried out. Anisotropic
thermal parameters were used for non-hydrogen atoms. All hydrogen
atoms were added in calculated positions with fixed isotropic contribu-
tions. All calculations were performed with use of teXsan crystal-
lographic software package of Molecular Structure Co. Table 1 gives
crystal data for the eight compounds. R values for some crystals are
moderately large, which would be due to poor crystal quality.
Band Calculation. To calculate intermolecular overlap integrals,
HOMO obtained by the extended Hu¨ckel MO calculation was used.18
The calculation was carried out with the use of semiempirical
parameters for Slater-type atomic orbitals.19 It has been assumed that
the transfer integral (t) is proportional to the overlap integral (S), t )
ꢀS (ꢀ ) -10 eV, ꢀ is a constant with the order of the orbital energies
of HOMO). The band structures were calculated based on the tight-
binding approximation.
Experimental Section
General. DIA,13 BEDT-TTF,14 and EDT-TTF15 were synthesized
by literature procedure. Chlorobenzene, methanol, ethanol, THF,
potassium hydroxide, sodium thiosulfate, tetraphenylphosphonium
chloride, n-butyllithium (in hexane), and tetra(n-butyl)ammonium
bromide were purchased from Wako Chem. Co. Ltd., iodine was
Electrical Resistivity Measurements. The d.c. resistivity measure-
ments were performed with the standard four-probe method. Gold leads
(10 or 15 µm diameter) were attached to the crystal with carbon paste.
(11) (a) Blanchard, P.; Duguay, G.; Cousseau, J.; Sall1, M.; Jubault, M.;
Gorgues, A.; Boubekeur, K.; Batail, P. Synth. Metals. 1993, 56, 2113-2117.
(b) Batsanov, A. S.; Bryce, M. R.; Cooke, G.; Dhindsa, A. S.; Heaton, J.
N.; Howard, J. A. K.; Moore, A. J.; Petty, M. C. Chem. Mater. 1994, 6,
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1667-1668.
Results and Discussion
The normal galvanostatic oxidation of solutions containing
donor molecules and supporting electrolytes was performed in
the presence of iodine-substituted neutral molecules (DIA, pBIB,
and/or TIE). By this procedure, (BEDT-TTF)2Cl(DIA) (1),
(BEDT-TTF)2Br(DIA) (2), (BEDT-TTF)2Cl2(DIA)(TIE) (3),
(12) Yamamoto, H. M.; Yamaura. J.; Kato. R. J. Mater. Chem. 1998,
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(16) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627-630.
(17) Sheldrick, G. M. Program for the Refinement of Crystal Structures;
University of Goettingen: Germany, 1993.
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(13) Franzen, V. Chem. Ber. 1954, 87, 1148-1154.
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