Modulation of charge-transfer complexes assisted by complementary hydrogen bonds of nucleobases: TCNQ complexes of a uracil-substituted EDO-TTF

Article abstract of DOI:10.1039/c2ce25889g

A hydrogen bond functionalized ethylenedioxytetrathiafulvalene (EDO-TTF) derivative having an n-butyluracil moiety was synthesized. In the crystal structure, the Watson-Crick-type complementary hydrogen bonds of the uracil moiety formed a pair of donor molecules, which further aggregated by S...S interactions and π-stacks of the TTF moiety to construct a two-dimensional sheet. In the charge-transfer complex formation with tetracyanoquinodimethane, the crystallization conditions modulated the subtle balance between Watson-Crick and reverse Watson-Crick types of complementary hydrogen-bonded pairs, controlling stoichiometry, ionicity and molecular packing of the complexes. A highly conducting mixed valence complex with the Watson-Crick-type hydrogen bonds was yielded by the quick evaporation of reaction solvent, and a low-conducting neutral complex forming reverse Watson-Crick-type hydrogen bonds was obtained by the slow vapor diffusion method. This journal is

Full text of DOI:10.1039/c2ce25889g

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PAPER
Modulation of charge-transfer complexes assisted by complementary
hydrogen bonds of nucleobases: TCNQ complexes of a uracil-substituted
EDO-TTF{
Tsuyoshi Murata, Yoshikazu Umemoto, Eigo Miyazaki, Kazuhiro Nakasuji and Yasushi Morita*
Received 4th June 2012, Accepted 21st July 2012
DOI: 10.1039/c2ce25889g
A hydrogen bond functionalized ethylenedioxytetrathiafulvalene (EDO-TTF) derivative having an
n-butyluracil moiety was synthesized. In the crystal structure, the Watson–Crick-type complementary
hydrogen bonds of the uracil moiety formed a pair of donor molecules, which further aggregated by
…
S
S interactions and p-stacks of the TTF moiety to construct a two-dimensional sheet. In the
charge-transfer complex formation with tetracyanoquinodimethane, the crystallization conditions
modulated the subtle balance between Watson–Crick and reverse Watson–Crick types of
complementary hydrogen-bonded pairs, controlling stoichiometry, ionicity and molecular packing of
the complexes. A highly conducting mixed valence complex with the Watson–Crick-type hydrogen
bonds was yielded by the quick evaporation of reaction solvent, and a low-conducting neutral
complex forming reverse Watson–Crick-type hydrogen bonds was obtained by the slow vapor
diffusion method.
We recently designed and synthesized TTF derivatives having
Introduction
nucleobase moieties as H-bonding units, and succeeded in the
construction of various self-assembled structures based on the
complementary H bonds of nucleobase moieties.12–15 In the
crystal structures of uracil-substituted TTF derivatives (TTF-U),
the subtle balance between Watson–Crick and reverse Watson–
Crick complementary H bonds of the uracil moiety (Fig. 1)16
were modulated by the redox states of the TTF moiety12b and the
substituent groups on the uracil moiety12c affecting the
molecular arrangements.
Organic charge-transfer (CT) complexes and salts based
on tetrathiafulvalene (TTF) and tetracyanoquinodimethane
(TCNQ) have provided various fascinating materials, such as
organic conductors and superconductors.1,2 Chemical modifica-
tions of the TTF skeleton have been performed to control its self-
assembling ability and intermolecular interactions to exhibit new
functions and phenomena.3 The ethylenedioxy (EDO) substitu-
tion on the TTF skeleton yielded several intriguing molecular
systems presenting new opportunities for functional CT com-
Furthermore,
a TTF-U derivative substituted with an
plexes and salts: self-assembling ability by the face-to-face C–
…
ethylenedithio group (EDT-TTF-U) afforded a highly conduc-
tive CT complex with TCNQ in which the self-assembled one-
dimensional channel structure provided the conduction path.15
The crystal structure of the (EDT-TTF-U)2TCNQ complex
indicates that the EDT substitution plays an important role in
H
O H–bonds on the EDO groups giving stable metallic states
in the BEDO-TTF complexes,4 and a peculiar phase transition
system with the multi-instability5 showing an ultrafast and highly
efficient photoresponse6 in the (EDO-TTF)2XF6 (X = P, As and
Sb) salts.
the construction of the one-dimensional channel by multiple
…
The introduction of hydrogen bond (H bond) interactions into
CT complexes and salts has served as an effective methodology
to control the molecular packing of conductive components.7–9
Furthermore, our recent investigations on H-bonded CT
complexes and salts have demonstrated that the molecular
recognition ability and high polarizability of H bonds can
modulate their electronic structures and physical properties.10,11
S
S interactions in addition to Watson–Crick type complemen-
tary H bonds of the uracil moiety.15 The preceding work by
Baudron et al. on F4TCNQ complexes of amido-functionalized
TTF derivatives revealed that the EDT and EDO substitution on
the TTF skeleton has significant effects on the D–A ratio,
molecular packing and physical properties by modulating self-
assembling abilities in addition to the redox abilities.9 In the
present study, for the exploration of further self-assembling
structures based on TTF nucleobases showing intriguing
phenomena, we have designed an EDO-substituted TTF-U
derivative (EDO-TTF-U). Here we describe the synthesis,
physical properties and crystal structures of EDO-TTF-U and
its TCNQ complexes. In the CT complex formation between
Department of Chemistry, Graduate School of Science, Osaka University,
Toyonaka, Osaka, 560-0043, Japan. E-mail: morita@chem.sci.osaka-u.ac.jp;
Fax: +81-6-6850-5395; Tel: +81-6-6850-5393
{ Electronic supplementary information (ESI) available: IR and Raman
spectra. CCDC reference numbers 886399 and 886400. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c2ce25889g
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uracil substitution on the redox ability is similar to those
observed in the TTF-U and EDT-TTF-U.12,15
Crystal structure of EDO-TTF-U
The single crystals of EDO-TTF-U suitable for X-ray crystal
structure analysis were obtained by the aerial evaporation from
CH2Cl2.{ The TTF skeleton is slightly distorted with bent angles
of 4.9–6.2u. The uracil moiety is nearly parallel to the TTF
skeleton with a dihedral angle of 9.6u.
The EDO-TTF-U molecules form a face-to-face dimer with a
˚
head-to-tail manner and an interplanar distance of 3.48 A
(Fig. 2a and 2b). The dimers are linked along the c-axis through
…
…
˚
complementary N–H OLC H bonds (N O distance, 2.82 A) of
the uracil moieties (Fig. 2c). The complementary H bonds in this
crystal is the Watson–Crick type, which are also observed in
the crystal structures of TTF-U and EDT-TTF-U.12a,15 The
…
H-bonded pairs are further connected by S S interactions on
Fig. 1 Watson–Crick and reverse Watson–Crick types of complemen-
tary H bonds of uracil.
EDO-TTF-U and TCNQ, two kinds of CT complexes exhibiting
Watson–Crick or reverse Watson–Crick H bonds were obtained
depending on the crystallization conditions, where the crystal
and electronic structures and physical properties were affected by
the complementary H bond types.
Results and discussions
Synthesis and electrochemical properties
Scheme 1 illustrates the synthetic procedure of EDO-TTF-U.
Lithiation of EDO-TTF using n-BuLi followed by the treatment
with Bu3SnCl afforded tributylstannylated EDO-TTF. EDO-
TTF-U was prepared by the Stille cross-coupling reaction of
tributylstannylated EDO-TTF with benzoyl-protected 5-iodo-1-
n-butyluracil in the presence of Pd(PPh3)4 and CuI catalysts
followed by the removal of the benzoyl group using MeNH2.
The cyclic voltammetry measurement of EDO-TTF-U shows
two-stage reversible one-electron oxidation processes. The
oxidation potentials of Eox1 = 20.03 V and Eox2 = +0.15 V vs.
Fc/Fc+ are closely similar to those of pristine EDO-TTF
(Eox1 = 20.02 V and Eox2 = +0.18 V). Such a small effect of
Fig. 2 Crystal structure of EDO-TTF-U. (a) Molecular packing viewed
along the c-axis. (b) Overlap mode in the p-stack dimer. (c) Two-
dimensional donor sheet on the (0, 0.5, 0) layer viewed along the b-axis.
n-Butyl groups were omitted for clarity in (a) and (c). Red and green
…
…
dotted lines present N–H OLC
respectively. Ellipsoids are drawn at the 50% probability level.
H
bonds and
S
S
interactions,
{ Crystallographic data for EDO-TTF-U: C16H16N2O4S4, M = 428.55,
monoclinic, space group P21/c (no. 14), a = 11.06(3), b = 16.45(4),
3
23
˚
˚
˚
c = 10.99(4) A, b = 111.4(2)u, V = 1863(10) A , Z = 4, Dc = 1.528 g cm
,
=
=
l = 0.71075 A, m(Mo-Ka) = 5.35 cm21, F(000) = 888, T = 200 K, 2hmax
54.96u, 4107 unique reflections of 14 973 collected (Rint = 0.1850), R1
0.0994 and Rw = 0.2333 [I > 2.0s(I)], S(GOF) = 0.928. Crystallographic
data for complex 2: C44H36N8O8S8, M = 1061.29, triclinic, space group
¯
˚
P1 (no. 2), a = 7.249(1), b = 10.373(2), c = 16.028(3) A, a = 89.459(9),
3
23
˚
b = 77.009(7), c = 79.014(8)u, V = 1152.0(4) A , Z = 1, Dc = 1.530 g cm
,
=
=
l = 0.71070 A, m(Mo-Ka) = 4.51 cm21, F(000) = 548, T = 93 K, 2hmax
54.0u, 4802 unique reflections of 9021 collected (Rint = 0.0447), R1
0.0447 and Rw = 0.1074 [I > 2.0s(I)], S(GOF) = 0.984.
˚
Scheme 1 Synthetic procedure of EDO-TTF-U.
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energy of this complex are 2.3 6 1024 S cm21 and 89 meV,
respectively.
˚
the TTF skeleton (3.57 A) to build up a two-dimensional donor
sheet (Fig. 2a and 2c).
Physical properties of TCNQ complexes
Crystal structure of (EDO-TTF-U)2(TCNQ) (2)
The CT complex formation between EDO-TTF-U and TCNQ
was performed by the direct mixing method in CH2Cl2. Two
kinds of CT complexes were obtained depending on the
crystallization process: quick evaporation of the reaction solvent
(complex 1, dark green powder) and slow vapor diffusion of
hexane into the reaction mixture (complex 2, black platelet
crystals).{ Both complexes were afforded selectively, and the
contamination of a complex with another one was not observed.
The donor–acceptor ratio of 1 was estimated as 1 : 1 by the
elemental analysis, and that of 2 was determined to be 2 : 1 in the
crystal structure (vide infra).
In the crystal structure of 2, one EDO-TTF-U and half a TCNQ
molecule are crystallographically independent, and the inversion
center is located at the TCNQ molecule.{ The r value of the
TCNQ molecule is estimated as 20.33 from bond lengths
(Table 1)21 and close to that obtained from the CN stretching
frequency. The central CLC bond length of the TTF skeleton of
˚
2 is 1.357(4) A, whose value is in the middle between those of
22
neutral EDO-TTF (1.318(3) A) and the cationic species in
˚
˚
(EDO-TTF)2PF6 at the low-temperature phase (1.381(5) A,
r = ca. +0.9)5a and is slightly shorter than that of the mixed
valence EDO-TTF in (EDO-TTF)2PF6 at the room-temperature
5a
phase (1.365(5) A, r = +0.5). These observations indicate the
˚
Fig. 3 illustrates the electronic spectra using KBr pellets of 1
and 2. The spectra of 1 and 2 show similar patterns at
wavenumber >10 000 cm21 originating from the intramolecular
transitions.17 The low-energy absorption bands assignable as the
intermolecular CT transition17 are observed around 3500 cm21
for 1 and 5500 cm21 for 2. The lower energy intermolecular CT
band of 1 indicates the mixed valence state with a segregated
stack. In the IR spectra of 1, the CMN stretching mode is
observed at 2191 cm21 indicating the highly ionized state of the
TCNQ moiety (Fig. S1{).18 The Raman spectrum of 1 shows two
bands at 1420 and 1454 cm21 assignable to CLC stretching
modes of the TCNQ and EDO-TTF skeletons, respectively (Fig.
S2{). The ionicity (r) of TCNQ is estimated to be 20.59 from the
slightly oxidated state of the donor molecule. The EDO-TTF-U
molecule is nearly planar with bent angles of 1.6–6.7u at the TTF
skeleton and a twist angle of 2.0u between uracil and TTF
moieties.
EDO-TTF-U and TCNQ molecules stack to form a one-
dimensional column in a D–A–D–D–A–D manner (Fig. 4a). The
˚
interplanar distance between donor and acceptor is 3.42 A
(Fig. 4b). The donor–donor stack has a head-to-tail manner, and
˚
the interplanar distance is 3.50 A (Fig. 4c).
The donor molecules form a pair with the complementary H
˚
bonds of 2.83 A (Fig. 4a and 4d). The H bond mode is the
reverse Watson–Crick type and different from that observed in
band at 1420 cm21 19
The frequency of the band of EDO-TTF
.
EDO-TTF-U itself (Fig. 2a). The H-bonded pairs are further
…
linked through the S S interactions (3.44 A) and p-stacks of the
˚
skeleton is slightly lower than that of (EDO-TTF)2PF6
(1472 cm21) in which EDO-TTF possesses +0.5 uniform
charge.20 This result indicates that the r value of EDO-TTF is
slightly larger than +0.5 and coincides with the r value of the
TCNQ moiety. In the electrical conductivity measurement for
the compressed pellet, 1 exhibits a high conductivity of 6.4 6
1022 S cm21 at room temperature (activation energy = 82 meV).
The r value of the TCNQ moiety in 2 is estimated as 20.40 from
the CMN stretching frequency in the IR spectra (2210 cm21, Fig.
S1{).18 These optical measurements indicate the neutral ground
state of 2. The room temperature conductivity and activation
TTF skeleton to form a two-dimensional donor sheet (Fig. 4d).
Complementary H-bonding modes in CT complexes
Fig. 5 compares the CLO stretching modes in the IR spectra of
neutral EDO-TTF-U, CT complexes 1 and 2. EDO-TTF-U
forming Watson–Crick type complementary H bonds (Fig. 2a)
shows two bands at 1716 and 1667 cm21 assignable as those of
C2LO and C4LO groups, respectively.23 In the case of 2 in which
reverse Watson–Crick type H bonds are observed (Fig. 4d), the
C2LO stretching mode shows a significant red-shift and appeared
at 1689 cm21 since the H bond formation softens the CLO bond.
The CLO stretching modes of 1 are observed at 1715 and
˚
Table 1 The C–C bond lengths (A) of TCNQ molecules in 2 and related
compounds
2
TCNQ0 a
TCNQN– b
a
b
c
d
1.349(5)
1.434(5), 1.440(5)
1.388(5)
1.433(5), 1.432(6)
0.484
20.33
1.346
1.448
1.374
1.441
0.476
0
1.373
1.426
1.420
1.416
0.500
21
rc
rd
a
b
c
d
Ref. 21a. Ref. 21b. r = c/(b + d). r = 2(r 2 r0)/(r1 2 r0); r0 and
Fig. 3 Electronic spectra of 1 and 2 in KBr pellets. Arrows indicate the
r1 are the r values calculated for TCNQ0 and TCNQN2, respectively.
intermolecular CT absorption bands.
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Fig. 5 CLO stretching modes in the IR spectra of EDO-TTF-U, 1 and 2
measured in KBr pellets.
complexes, quick evaporation (1) and slow vapor diffusion (2),
probably affected the subtle balance of two H-bonding types,
and caused the generation of two types of CT complexes. The
differences in the H bond types modulate the molecular
arrangements and electronic structures of CT complexes to
achieve the highly conducting segregated stack of 1 and the low-
conducting mixed stack of 2. Similar complex formation
behaviors, ‘‘monotropic complex isomerism’’ where a donor–
acceptor pair affords multiple kinds of CT complexes having
different crystal structures, ionicities and physical properties
depending on the preparation conditions, have been also
observed for several donor–acceptor type CT complexes.25–29 It
has been known that such complex isomerisation is usually
achieved for donor–acceptor systems locating at the vicinity of
the redox boundary between neutral and mixed valence CT
complexes (difference of the redox potentials between donor and
Fig. 4 Crystal structure of complex 2. (a) One-dimensional p-stacking
column viewed along the a-axis. (b and c) Overlap modes of donor–
acceptor and donor–donor stacks in the one-dimensional column,
respectively. (d) Two-dimensional donor sheet formed by the comple-
…
mentary H–bonds, S S interactions and p-stacks on the (0, 0, 0) plane
viewed along the b-axis. n-Butyl groups were omitted for clarity in (d).
…
acceptor (DE)
= +0.34 V for conventional TTF-TCNQ
…
Red and green dotted lines present the N–H OLC H bonds and S
interactions, respectively. Ellipsoids are drawn at the 50% probability
S
systems).30 Surprisingly, the DE value between EDO-TTF-U
and TCNQ (Ered = 20.11 V vs. Fc/Fc+) is +0.08 V from the CV
measurement, and much smaller than those of monotropic com-
plex isomer systems. The complex formation of EDO-TTF-U
with TCNQ implies that not only the redox valance between
donor and acceptor molecules but also the structural modifica-
tion by complementary H bond types are important factors in
controlling the ionicity of a CT complex.
level.
1671 cm21 and are close to those of EDO-TTF-U and (EDT-
TTF-U)2TCNQ complexes15 both of which exhibit Watson–
Crick type complementary H bonds between donor molecules in
the crystal structures. These results indicate that the uracil
moiety in 1 forms the Watson–Crick type complementary H
bonds. It is expected that the formation of additional H bonds
causes a further low-frequency shift of the CLO stretching
modes. Therefore, the similarity of these bands in EDO-TTF-U
and 1 can eliminate the possibility of H bond formation between
CLO groups and crystalline water molecules.
It has been known that the difference of stabilization energies
of these two H-bonding motifs is small.24 Actually, our previous
investigations on TTF-U derivatives revealed that both types of
complementary H bonds can be formed depending on the redox
state of the TTF skeleton12b and the substituent groups at the N1
atom.12c The stabilization energy calculated for the H-bonded
pairs in the crystal structures are close to each other (210.9 kcal
mol21 for Watson–Crick type pair (EDO-TTF-U) and
210.2 kcal mol21 for reverse Watson–Crick type pair (2)). In
the present case, the crystallization methods of the TCNQ
In the crystal structures of EDT-TTF-U and (EDT-TTF-
U)2(TCNQ) complex, the Watson–Crick type complementary H
…
bonds on the uracil moiety and multiple S S interactions on the
EDT-TTF skeleton form one-dimensional chains.15 Further
assembly of the chains builds up a one-dimensional channel in
(EDT-TTF-U)2(TCNQ) (Fig. 6). In the case of EDO-TTF-U,
…
the self-assembling ability by S S interactions is diminished due
…
to the EDO substitution, and only a single S S interaction is
formed between adjacent TTF skeletons, resulting in the
construction of diverse network structures. The difference of
molecular packing of (EDT-TTF-U)2(TCNQ) and 2, one-
dimensional channel structure and D–D–A mixed stack,
respectively, would originate from the differences of self-
assembling ability of the TTF skeleton in addition to the
complementary H bonding types.
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was taken at 70 eV by using a Shimadzu QP-5000 mass
spectrometer. The infrared spectra were recorded on a JASCO
FT/IR-660 Plus spectrometer using KBr plates (resolution
2 cm21). The electronic spectra were measured by a Shimadzu
UV-3100PC spectrometer using KBr plates. Measurement of
Raman spectrum was carried out for the powder sample of
1 using a JASCO NR1800 (resolution 2 cm21) with the excitation
wavelength of 632.8 nm (He–Ne line). Elemental analyses were
performed at the Graduate School of Science, Osaka University.
Temperature dependencies of electrical conductivity were mea-
sured for compressed pellets of 1 and 2 by four- and two-probe
methods, respectively, in a temperature range of 100–300 K
using a Fuso dc multi-channel conductivity device HECS 944C
type.
Fig. 6 One-dimensional chain of EDT-TTF-U formed by the Watson–
…
Crick type complementary H bonds (red dotted lines) and multiple S
interactions (green dotted lines).15
S
Modified synthetic procedure of EDO-TTF
Conclusions
Bis(methoxycarbonyl)EDO-TTF31 (1.46 g, 3.86 mmol) and
LiBr?H2O (4.92 g, 48.3 mmol) was dissolved in N,N-
dimethylacetamide (110 mL). The mixture was gradually
warmed up to 150 uC, then stirred at the temperature for
20 min. After cooling to room temperature, water (200 mL)
was poured to the reaction mixture, and extracted with CS2
(80 mL 6 3). The combined organic extracts were dried over
Na2SO4, then filtered and concentrated under reduced pressure.
The residual oil was subjected to a silica gel column chromato-
graphy with CS2 as eluant, to give EDO-TTF (202 mg, 20%) and
mono(methoxycarbonyl)EDO-TTF (822 mg, 66%). The same
procedure was performed for mono(methoxycarbonyl)EDO-
TTF (700 mg, 2.18 mmol) using LiBr?H2O (1.37 g, 13.1 mmol)
and N,N-dimethylacetamide (60 mL), to give EDO-TTF
(232 mg, 57%) as a red powder.
We have synthesized an EDO-TTF derivative having a uracil
moiety as an H bonding unit and investigated the physical
properties of TCNQ complexes. In the crystal structures, the self-
assembling nature of EDO-TTF-U originating from the com-
…
plementary H bonds inherent in nucleobases, S S interactions
and p-stacks of the TTF moieties constructed two-dimensional
donor sheets. The EDO substitution modulated the self-
assembling ability of the TTF skeletons and increased the
variation of the supramolecular assemblies of the TTF–
nucleobase system. In the CT complex formation with TCNQ,
the crystallization conditions produced the highly conducting
complex with a segregated structure (1) and low-conducting
complex with a mixed stacking column (2). The observation of
Watson–Crick and reverse Watson–Crick type complementary
H bonds in 1 and 2, respectively, indicates the importance of self-
assembling ability of nucleobases in the control of electronic
structures and physical properties of CT complexes. The crystal
structure analysis of the highly conducting complex 1 is
indispensable for the elucidation of the effect of complementary
H bonds on the ionicity and molecular packing and is currently
in progress.
Synthesis of EDO-TTF-U
EDO-TTF (193 mg, 0.74 mmol) was placed in a Schlenk tube
and dissolved with THF (10 mL). To this mixture was added
n-BuLi (1.6 M hexane solution, 0.55 mL, 0.88 mmol) at 278 uC
and stirred at this temperature for 1 h. Bu3SnCl (0.21 mL,
0.74 mmol) was added to this mixture, and the reaction mixture
was gradually warmed up to room temperature over 0.5 h. To
the resulting mixture was added a pH 7.0 phosphate buffer
solution (0.1 M, 20 mL). The organic layer was separated, and
the aqueous layer was extracted with ethyl acetate (30 mL 6 3).
The combined organic extracts were dried over Na2SO4, then
filtered and concentrated under reduced pressure. The residual
oil was dried in vacuo at room temperature, to give Bu3Sn-
substituted TTF as a yellow oil.
The resulting oil, N3-benzoyl-N1-n-butyl-5-iodouracil (293 mg,
0.74 mmol), Pd(PPh3)4 (86 mg, 0.074 mmol) and CuI (42 mg,
0.22 mmol) were dissolved in THF (10 mL) in a Schlenk tube
equipped with a reflux condenser, and the resulting mixture was
refluxed for 4 h. After cooling to room temperature, the solvent
was removed by evaporation, and then extracted with ethyl
acetate (20 mL) and a saturated KF aqueous solution (20 mL).
The organic extract was washed with a saturated KF aqueous
solution (20 mL 6 2) and water (20 mL 6 2). The combined
organic extracts were dried over Na2SO4, then filtered and
concentrated under reduced pressure. The residual powder was
purified by a silica gel column chromatography with 5 : 1
Experimental
Materials and measurements
N3-Benzoyl-N1-n-butyl-5-iodouracil was prepared according to
our previous paper.15 EDO-TTF was synthesized by the
previously reported procedure.31 The decarboxylation reaction
of bis(methoxycarbonyl)EDO-TTF was modified in our
laboratory, where the reaction solvent was changed to
N,N-dimethylacetamide from harmful hexamethylphosphora-
mide (vide infra). All reactions requiring anhydrous conditions
were performed under an argon atmosphere. Solvents were dried
and distilled under an argon atmosphere prior to use.
The Rf value on TLC was recorded on E. Merck pre-coated
(0.25 mm) silica gel 60 F254 plates. The plate was sprayed with a
solution of 10% phosphomolybdic acid in 95% ethanol and then
heated until the spots became clearly visible. The melting point
1
was measured with a hot-stage apparatus and uncorrected. H
NMR spectrum was obtained on a JEOL EX-270 with DMSO-
d6 using Me4Si as an internal standard. The EI-Mass spectrum
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hexane–ethyl acetate and ethyl acetate, to give a mixture
containing the benzoyl-protected EDO-TTF derivative (165 mg).
The resulting mixture was placed in a Schlenk tube, then
dispersed in 30% MeNH2 MeOH solution (3 mL), and stirred at
room temperature for 2.5 h. After being cooled to 0 uC, the
solution was neutralized by acetic acid. The resulting precipitate
was collected by filtration, then washed with MeOH to give
EDO-TTF-U (84 mg) as a reddish orange powder in 27% yield in
three steps from EDO-TTF: mp 203–204 uC (dec); TLC Rf 0.49
(1 : 1 hexane–ethyl acetate); 1H NMR (DMSO-d6) d 0.89 (t, J =
7.3 Hz, 3H), 1.23–1.31 (m, 2H), 1.51–1.59 (m, 2H), 3.72 (t, J =
7.2 Hz, 2H), 4.30 (s, 2H), 7.35 (s, 1H), 7.85 (s, 1H); EI-MS, m/z
312 (M+–OCH2CH2O–C4H9, 100%), 428 (M+, 30%); IR (KBr)
3250–2700, 1716, 1667, 1456, 1164 cm21; UV (KBr) 428, 300 nm.
factors ranging from 0.740 to 0.984 for EDO-TTF-U and from
0.577 to 0.914 for complex 2. Structures were determined by a
direct method using SIR-2004.32 Least-squares refinement was
performed on F2 with SHELXL-97.33 All non-hydrogen atoms
were refined anisotropically. Positional parameters of hydrogen
atoms were calculated with sp2 or sp3 configuration of the
bonding carbon and nitrogen atoms, and hydrogen atoms were
refined using the riding model. In the refinement procedures,
isotropic temperature factors with magnitudes of 1.2 times of the
equivalent temperature factors of the bonding atoms were
applied for hydrogen atoms.
Theoretical calculation
Density functional theory (DFT) calculations were performed at
the RB3LYP/6-31G(d) level on Gaussian 98. The DFT calcula-
tions of H-bonded pairs were performed using the structures
extracted from the crystal structures.
Preparation of (EDO-TTF-U)(TCNQ) (1)
To a solution of EDO-TTF-U (7.1 mg, 0.017 mmol) in CH2Cl2
(10 mL) in a 50 mL round-bottomed flask, TCNQ (7.3 mg,
0.036 mmol) was added at room temperature. The reaction mixture
was concentrated under reduced pressure. The residual powder was
suspended in a small amount of CH2Cl2, then collected by filtration
to give the complex 1 (6.5 mg) as a dark green powder: mp 212–
214 uC (dec); IR (KBr) 3100–2700, 2191(sh), 2180, 1715, 1671, 1559,
1507, 1165 cm21; UV (KBr) 316, 372, 766, 844, 2422 nm; Anal.
Calcd for (C16H16N2O4S4)(C12H4N4)(H2O)0.5: C, 52.40; H, 3.30; N,
13.09%. Found: C, 52.54; H, 3.24; N, 12.71%. Since rapid
precipitation from the reaction was required to afford 1, single
crystals suitable for X-ray crystal structure analysis and conductiv-
ity measurements could not be obtained. Structural information
could not be achieved even by the X-ray diffraction study on the
powder sample.
Acknowledgements
This work was partly supported by Grants-in-Aid for Scientific
Research (23750039) from the Japan Society for the Promotion
of Science, and for Scientific Research on Innovative Area
(20110006) and Elements Science and Technology Project from
the Ministry of Education, Culture, Sports, Sciences and
Technology, Japan. We thank Professor M. Kawano and Dr
Y. Yakiyama, Pohang University of Science and Technology
(POSTECH), for their technical assistance on the structural
analysis.
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