Structural study and electrical conductivity of salts based on functionalized TTF containing peripheral selenium atoms

Article abstract of DOI:10.1039/B308514G

Five new substituted tetrathiafulvalene derivatives containing the acetoxyphenyl group as a side-chain have been synthesized using a Wittig-type condensation. Four of them contain peripheral selenium atoms. From cyclic voltammetry data, the electron donor abilities of the obtained compounds have been found to be similar to that of BEDT-TTF. The crystal structures of three of these new donors have been determined. A series of radical cation salts derived from these donors has been obtained by electrocrystallization; the electrical conductivity of these phases measured on compressed powder pellets range from 5 x 10^-4 to 4 x 10^-5 S cm^-1. Charge transfer complexes have also been chemically prepared by using TCNQ as an electron acceptor; the electrical conductivity of their compressed powders range from 0.3 to 0.5 S cm^-1. The crystal structure of one of these charge transfer complexes has been determined and shows that the donor and the acceptor entities form regular segregated stacks; its rather high conductivity, actually measured on powder, is in agreement with this structural feature.

Full text of DOI:10.1039/B308514G

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A R T I C L E
Structural study and electrical conductivity of salts based on
functionalized TTF containing peripheral selenium atoms{
Lakhemici Kaboub,a,c Jean-Pierre Legros,b Bruno Donnadieu,b Abdel-Krim Gouasmia,c
Louiza Boudibac and Jean-Marc Fabre*a
aLaboratoire de Chimie Organique: He´te´rochimie et Materiaux Organiques, UMR 5076,
ENSCM 8 rue de l’Ecole Normale, F 34296 Montpellier cedex-5, France.
E-mail: jmfabre@cit.enscm.fr
bLaboratoire de Chimie de Coordination, CNRS-UPR 8241, 205 route de Narbonne,
F 31077 Toulouse cedex-4, France. E-mail: legros@lcc-toulouse.fr
cLaboratoire de Chimie des Mate´riaux Organiques, Centre Universitaire de Te´bessa,
route de Constantine, 12000, Te´bessa (Alge´rie)
Received 23rd July 2003, Accepted 11th November 2003
First published as an Advance Article on the web 5th January 2004
Five new substituted tetrathiafulvalene derivatives containing the acetoxyphenyl group as a side-chain have
been synthesized using a Wittig-type condensation. Four of them contain peripheral selenium atoms. From
cyclic voltammetry data, the electron donor abilities of the obtained compounds have been found to be similar
to that of BEDT-TTF. The crystal structures of three of these new donors have been determined. A series of
radical cation salts derived from these donors has been obtained by electrocrystallization; the electrical
conductivity of these phases measured on compressed powder pellets range from 5 6 1024 to 4 6 1025 S cm21
Charge transfer complexes have also been chemically prepared by using TCNQ as an electron acceptor; the
electrical conductivity of their compressed powders range from 0.3 to 0.5 S cm21. The crystal structure of one
of these charge transfer complexes has been determined and shows that the donor and the acceptor entities
form regular segregated stacks; its rather high conductivity, actually measured on powder, is in agreement with
this structural feature.
.
and (ii) containing, in some cases, peripheral selenium
atoms which may induce two-dimensional intermolecular
interactions.
Introduction
Over the last few years, the main research topics in the field of
conducting organic materials have been devoted to the
stabilization of their metallic state by increasing their
dimensionality.1,2 This has been achieved in particular by
introducing functions such as amine, alcohol, ester or amide
onto tetrathiafulvalene (TTF) derivatives used as precursors.3–8
Therefore, many functionalized molecules derived from TTF
have been prepared and used more or less successfully.
In some cases, radical cation salts, based on TTF derivatives
functionalized by one or two hydroxylated chains, were
obtained as semi-conducting materials; in spite of the existence
The synthesis, electrochemical behaviour and structural
characterization of these precursors containing an ester group,
and the synthesis and electrical characterization of their radical
cation salts and charge transfer complexes with TCNQ are
reported below. The structural study of the charge transfer
complex (Ic)2TCNQ is also reported. Moreover, it is worth
noting that compounds I are also interesting precursors to the
corresponding hydroxylated-TTF (hydroxyphenyl group)9,10
and to singly bridged bis-TTF involving the ester group as a
linker.11,12
…
…
of (donor anion donor) interactions involving the OH
groups, very weak electronic delocalization occurred. More-
over, the absence of a mixed valence state within the salts and
unfavourable stacking modes of the TTF units due to steric
hindrance induced by the chains attached to the TTF core may
explain the poor conductive properties of the compounds.7
Conversely, in other cases, for instance, when TTF units
bear an amide function (–CONH2 and –CONHR), highly
conducting salts were obtained.5,6 These salts exhibited a
structure consisting of stacks of organic molecules that allows
the necessary electronic delocalization as well as effective
Experimental
…
…
Synthesis
(donor anion donor) interactions giving rise to the required
two-dimensional character responsible for the stabilization of
their metallic state down to 0.47 K.6
Compounds I were prepared using the Wittig-type condensa-
tion13–15 described in Scheme 1.
The starting salts (type 113 and 29) were isolated following
the appropriate procedures described in the literature.13,9 The
Wittig condensation was then carried out in acetonitrile at
room temperature using a triphenylphosphonium salt 1 and a
dithiolium salt 2 in the presence of triethylamine.16,17 As
expected, the reaction provided a mixture containing mainly
Within this framework, we developed and studied a series of
TTF derivatives I (i) functionalized by the acetoxyphenyl group
{ Electronic supplementary information (ESI) available: rotatable 3-D
crystal structure diagrams and a table of selected torsion angles for Ic–e
and (Ic)2–TCNQ. See http://www.rsc.org/suppdata/jm/b3/b308514g/
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 5 1 – 3 5 6
3 5 1

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withdrawing effects of both the acetoxyphenyl substituent and
the hydrocarbonselenium chains (or cycle) in donors I are
almost compensated by the opposite effect of the methyl group
also present on the TTF core.
Synthesis and characterization of salts and complexes derived
from donors I
Tentative preparation and characterization of some radical
cation salts derived from compounds I were undertaken. A few
perchlorate, triiodide and hexafluorophosphate salts were
obtained as crystals of poor quality by electrocrystallization
of donors Ib, Ic and Ie in an organic solvent. The radical cation
salts were prepared by galvanostatic electrochemical oxidation
of donors I at a platinum electrode, in a 15 ml U-shaped cell
containing a glass frit membrane, using n-Bu4NClO4, n-Bu4NI3
or n-Bu4NPF6 (0.5 M in THF) as the supporting electrolyte
and by applying a current within the range 3–5 mA (0.25–
0.40 mA cm2). In addition, some charge transfer complexes
were isolated by a chemical redox reaction between a donor of
the type I series and TCNQ as the electron acceptor.1,2 In each
experiment, equimolar amounts (0.1 mmol.) of donor I and
TCNQ were separately dissolved in boiling acetonitrile and
then mixed. The resulting dark solution was then stored at
room temperature for several days. The precipitate was then
separated by filtration and analysed.18,19 One of these
complexes, i.e. (Ic)2TCNQ, was obtained as plate-like crystals
of sufficient quality to undergo a structural study by X-ray
diffraction.
Scheme 1
the target compound I which was separated from the two
symmetrical species by column chromatography on silica gel
using CH2Cl2–hexane (1 : 2) as eluent. The pure samples were
isolated in quite a low yield and analysed by mass spectro-
metry, 1H-NMR and elemental analysis as reported in Table 1.
Electrochemical characterization
The redox properties of compounds Ia–Ie were determined by
cyclic voltammetry. Each experiment was performed on a
platinum electrode, in dry CH2Cl2 at room temperature, with a
SCE reference electrode and n-Bu4NPF6 as the supporting
electrolyte. A scan rate of 100 mV s21 was used. As expected,
all compounds show two one-electron reversible waves. The
half-wave potentials E ox1 and E ox2 are reported in Table 2.
½
½
The E ox1 values of compounds Ia–Id are found to be lower
½
than that of BEDT-TTF (0.620 V) taken as a reference. This is
indicative of good electron donor abilities which make these
compounds suitable for use in the synthesis of charge-transfer
complexes and radical cation salts.
It is also interesting to note that going from compound Ib to
compound Id the E ox1 value is shifted towards less anodic
potentials as the ring strain of the peripheral heterocycles
decreases. Moreover, when compared with the redox potentials
of the unsubstituted parent compound TTF (E ox1 ~ 0.495 V;
The electrical conductivities of the isolated radical cation
salts and charge transfer complexes were measured using a
two-probe technique20 on compressed pellets. The results are
collected in Table 3.
½
Crystal structure determinations
˚
Graphite-monochromated Mo-Ka radiation (l ~ 0.71073 A)
was used for all measurements. Diffraction data sets for Id and
(Ic)2–TCNQ were collected at room temperature using a CAD4
½
E ox2 ~ 0.936 V), these data show that the combined electron
½
Table 1 Characteristics of compounds Ia–Ie
Compound I
Yield (%)
15
Mp/uC
1H-NMR (CDCl3, ppm)
Mass Spec.
M1: 538
Elemental Analysis (%) Calcd/Found
Ia: R ~ R ~ CH3
C17H16O2S4Se2
116
2.03 (s, 3H): CH3
C 37.92; H 2.97
C 37.78; H 2.95
2.31 (s, 3H): CH3CO
2.33 (s, 6H): 2 6 SeCH3
7.23 (m, 4H): C6H4
2.03 (s, 3H): CH3
2.31 (s, 3H): CH3CO
4.93 (s, 2H): SeCH2Se
7.22 (m, 4H): C6H4
2.03 (s, 3H): CH3
2.31 (s, 3H): CH3CO
3.31 (s, 4H): (CH2)2
7.20 (m, 4H): C6H4
2.02 (s, 3H): CH3
2.31 (s, 3H): CH3CO
2.76 (m, 6H): (CH2)3
7.22 (m, 4H): C6H4
2.04 (s, 3H): CH3
Ib: R–R ~ –CH2–
C16H12O2S4Se2
12
20
16
31
148
164
193
161
M1: 522
M113: 539
M1: 550
M1: 402
C 36.78; H 2.29
C 36.67; H 2.46
Ic: R–R ~ (CH2)2
C17H14O2S4Se2
C 38.05; H 2.61
C 38.17; H 2.60
Id: R–R ~ (CH2)3
C18H16O2S4Se2
C 38.27; H 2.90
C 38.91; H 2.86
Ie: R’–R’ ~ (CHLCH)2
C19H14O2S4
C 56.71; H 3.48
C 56.40; H 3.36
2.30 (s, 3H): CH3CO
7.09 (m, 4H): Benzo
7.30 (m, 4H): C6H4
Table 2 Half-wave potentials of compounds Ia–Ie
Compound I
BEDT-TTFa (reference)
Ia
Ib
Ic
Id
Ie
E ox1/V
½
E ox2/V
½
0.620
1.039
0.542
0.984
0.562
1.018
0.558
1.014
0.548
1.017
0.632
1.099
a BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene. Cyclic voltammetry measurements were performed in CH2Cl2 on a Pt electrode versus SCE
at room temperature with NBu4PF6 (0.1 M) as the supporting electrolyte. A scan rate of 100 mV s21 was used.
3 5 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 5 1 – 3 5 6

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Table 3 Characteristics and electrical conductivities of complexes and salts derived from donors of type I
Donor (type I)
Ia
Ib
Ic
Id
Ib
Ic
Ic
Ie
Ie
TCNQ or anion
Mp/uC
TCNQ
148
Green
Ndl
0.3
TCNQ
188
Black
Pwd
0.4
TCNQ
169
Black
Plt
0.5
TCNQ
180
ClO4
220
ClO4
200
I3
170
PF6
168
I3
220
Black
Pwd
Colour Morphologya
Black
Pwd
Green
Pwd
Black
Ndl
Black
Pwd
Black
Plt
s/S cm21b
6 6 1027
1 6 1025
5 6 1024
4 6 1025
1 6 1025
9 6 1025
a Ndl ~ needles, Pwd ~ powder, Plt ~ platelets. b Electrical conductivity: measurements achieved on compressed pellets using a two probe
technique.
Table 4 Crystal data and structure determination details for Ic, Id, Ie, and (Ic)2–TCNQ
Compound
Ic
Id
Ie
(Ic)2–TCNQ
Formula
M
C17H14O2S4Se2
536.4
C18H16O2S4Se2
550.5
C19H14O2S4
402.5
C23H16N2O2S4Se2
638.5
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/c
Monoclinic
I2/a (nu 15)c
30.154(8)
4.052(4)
39.317(9)
91.40(3)
4802(5)
˚
a/A
10.4533(6)
17.2668(9)
11.5179(6)
112.10(1)
1926.1(2)
4
6.641(2)
23.033(5)
13.830(3)
101.19(2)
2075.2(9)
4
15.0129(8)
9.4620(6)
13.3550(8)
109.64(1)
1786.8(2)
4
˚
b/A
˚
c/A
b/u
V/A
3
˚
Z
8
3.45
m/mm21
4.30
3.98
0.54
Measured/independent refl. (Rint
Observed refl. [I w 2s(I)]
R(F)a (observed refl.)
Rw(F2)b (all refl.)
)
33791/4550 (0.051)
3582
0.036
4428/4071 (0.036)
2102
0.033
30356/4272 (0.079)
3855
0.050
5512/2945 (0.076)
1715
0.048
0.100
0.126
0.138
0.131
a R(F) ~ S ||Fo| 2 |Fc||/S|Fo|. b Rw(F2) ~ {S[w(Fo 2 Fc2)2]/S[w(Fo
setting is C2/c. The setting I2/a has been chosen to reduce correlations during the refinement process. The unit cell parameters in C2/c are a ~
) .
]}1/2 c I2/a is a non-standard setting of space group nu 15, the standard
2
2 2
˚
˚
˚
48.95 A, b ~ 4.05 A, c ~ 30.15 A, b ~ 126.6u.
Enraf-Nonius diffractometer; data sets for Ic and Ie were
collected at 180 K using a Xcalibur Oxford Instrument CCD
diffractometer equipped with a nitrogen gas flow cooling
device. Crystal data and relevant data collection and refine-
ment parameters are listed in Table 4.{ All intensity data were
corrected for absorption. Structure solution and refinement
(against F2 using all reflections) were performed using standard
procedures.21–23
All non-hydrogen atoms were refined anisotropically,
hydrogen atoms were located on difference-Fourier maps
and their contributions were included in structure factor
calculations using calculated positions and the riding model
with isotropic temperature factors (not refined). However, for
(Ic)2–TCNQ, the carbon atoms were refined isotropically
because of the small number of observed reflections and of the
poor quality of the crystal.
ring and the TTF core, the molecule Ie is almost planar with the
exception of the phenyl ring bearing the acetoxyphenyl group.
Owing to the free rotation allowed around the C(6)–C(7) and
C(10)–O(1) bonds, it is surprising that the acetyl group lies
almost exactly in the plane of the TTF core [the largest
deviation from the plane defined by atoms S(1), S(2), S(3), S(4),
˚
C(3), C(4) is 20.12 A for the outermost atom C(14)]. The other
donor molecules Id and Ic are significantly bent and have a
boat conformation. Taking as a reference the plane of the TTF
core defined by atoms S(1), S(2), S(3), S(4), C(3), C(4) and
setting as positive the rotation that brings atoms above this
plane, the Id molecule displays angles a1 ~ 221.5u and a2 ~
215.0u between the reference plane and the mean planes
through atoms S(1), S(2), C(1), C(2), Se(1), Se(2) on one side
and atoms S(3), S(4), C(5), C(6), C(7), C(15) on the other side,
respectively. The same angles are a1 ~ 121.2u and a2 ~ 119.5u
respectively for Ic.
Several TTF derivatives, in their neutral form, have been
reported to adopt, in the solid state, such a boat conformation,
for example BEDT-TTF [bis(ethylenedithio)tetrathiafulva-
lene],25 BEDO-TTF [bis(ethylenedioxo)tetrathiafulvalene],26
EDT-TTF (ethylenedithiotetrathiafulvalene),27 EDS-TTF
(ethylenediselenotetrathiafulvalene),28 or, more recently,
ETEDT-TTF (ethylenethioethylenedithiotetrathiafulvalene).29
A theoretical study by Whangbo et al.30 on BEDT-TTF and
BEDO-TTF has indicated that the most stable configuration
for the isolated molecule would be the planar one (ethylene
residues excluded), but the energy required to fold the molecule
would be rather small and could be afforded by weak
Results and discussion
For discussion of the crystal structures, atoms are numbered
according to Fig. 1. Selected bond lengths and angles are given
in Table 5.
Neutral donors
The crystal structures of Ie, Id and Ic are shown on Figs. 2, 3
and 4 respectively.24 In these structures the molecules have not
formed stacks. The most striking feature is the difference in the
conformations of these apparently closely related molecules.
This is emphasized by comparison of the side view of the
molecules shown in Fig. 5. A table of selected torsion angles
(Table 6) has been deposited as supplementary material.{24
Probably, because of the conjugation between the external
…
…
intermolecular interactions such as C–H S (or C–H O). In
…
…
Ie no intermolecular S S and only one H S short distance
(i.e. shorter than—but very close to—the sum of the van der
…
˚
Waals radii) is observed [C(15)–H S(4): 2.843 A]. In Id there
…
is no intermolecular chalcogen chalcogen short distance but
…
…
…
three C–H chalcogen contacts are observed [C(15)–H S(3):
…
{ CCDC reference numbers 216047–216050. See http://www.rsc.org/
suppdata/jm/b3/b308514g/ for crystallographic data in .cif or other
electronic format.
˚
2.905 A, C(12)–H Se(1): 3.031 A, C(14)–H Se(1): 2.959 A].
˚
˚
In Ic several intermolecular short distances are found
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 5 1 – 3 5 6
3 5 3

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˚
Table 5 Selected interatomic distances (A) and bond angles (u) for Ie,
Id, Ic, and (Ic)2–TCNQ (e.s.d.’s in parentheses). For the sake of brevity
C–C bond lengths of the phenyl rings are not listed and only bond
angles involving the outermost atoms are reported. See Fig. 1 for
i
numbering. Superscript indicates an inversion through a centre of
symmetry
Distances
Ie
Id
Ic
(Ic)2–TCNQ
Se(1)–C(1)
Se(1)–C(17)
Se(2)–C(2)
Se(2)–C(16)
S(1)–C(1)
S(1)–C(3)
S(2)–C(2)
S(2)–C(3)
S(3)–C(4)
S(3)–C(5)
S(4)–C(4)
S(4)–C(6)
O(1)–C(10)
O(1)–C(13)
O(2)–C(13)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(5)–C(15)
C(6)–C(7)
C(13)–C(14)
C(1)–C(19)
C(2)–C(16)
C(16)–C(17)
C(16)–C(18)
C(17)–C(18)
C(18)–C(19)
C(20)–C(21)
C(20)–C(22)
C(20)–C(23)
C(23)–C(24)
C(23)–C(25)
—
1.893(5)
1.966(6)
1.900(5)
1.948(7)
1.757(5)
1.762(6)
1.748(5)
1.764(5)
1.752(5)
1.750(5)
1.734(5)
1.771(5)
1.406(7)
1.294(10)
1.202(11)
1.327(7)
1.335(7)
1.333(7)
1.506(7)
1.474(6)
1.461(10)
1.887(3)
1.974(4)
1.892(3)
1.952(3)
1.757(3)
1.756(3)
1.751(3)
1.758(3)
1.758(3)
1.762(3)
1.753(3)
1.770(3)
1.407(4)
1.350(4)
1.185(5)
1.344(5)
1.342(4)
1.342(5)
1.511(5)
1.484(5)
1.488(5)
1.877(7)
1.943(9)
1.883(7)
1.944(9)
1.752(7)
1.739(7)
1.748(8)
1.745(7)
1.731(7)
1.731(8)
1.735(7)
1.761(7)
1.404(8)
1.348(10)
1.190(11)
1.308(9)
1.349(10)
1.356(11)
1.504(12)
1.460(10)
1.477(11)
—
—
—
—
1.750(2)
1.755(2)
1.759(2)
1.757(2)
1.762(2)
1.753(2)
1.753(2)
1.766(2)
1.400(3)
1.365(3)
1.194(4)
1.397(3)
1.347(3)
1.343(3)
1.501(3)
1.479(3)
1.491(4)
1.398(4)
1.400(3)
1.387(4)
—
—
—
—
—
1.469(5)
—
1.457(13)
—
—
—
1.387(4)
1.387(4)
1.517(10)
1.501(10)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1.431(11)
1.409(11)
1.420(10)
1.416(10)
1.420(9)
1.340(11)
1.135(11)
1.118(11)
—
—
—
—
—
—
—
i
C(24)–C(25 )
N(1)–C(21)
N(2)–C(22)
Angles
Ie
Id
Ic
(Ic)2–TCNQ
118.5(6)
122.1(7)
111.6(7)
126.3(8)
119.1(6)
119.7(7)
—
—
—
—
—
C(10)–O(1)–C(13) 119.9(2)
O(1)–C(13)–O(2) 123.3(3)
O(1)–C(13)–C(14) 110.2(2)
O(2)–C(13)–C(14) 126.4(3)
Se(1)–C(17)–C(16)
Se(2)–C(16)–C(17)
Se(2)–C(16)–C(18)
Se(1)–C(17)–C(18)
C(16)–C(18)–C(17)
C(2)–C(16)–C(17) 118.9(2)
C(16)–C(17)–C(18) 120.7(3)
C(17)–C(18)–C(19) 120.9(3)
C(18)–C(19)–C(1) 118.9(2)
121.7(6)
120.1(8)
115.9(7)
124.0(8)
—
117.6(3)
123.1(3)
110.9(3)
126.0(3)
118.1(3)
114.1(3)
—
—
—
—
—
—
—
—
—
—
—
116.7(5)
116.5(4)
115.5(6)
—
—
—
Fig. 1 Numbering scheme of the atoms used throughout the X-ray
study. For the carbon atoms the symbol C is omitted for clarity.
—
—
—
—
—
…
…
…
˚
˚
[Se(1) Se(2): 3.574 A, Se(1) S(1): 3.680 A, Se(2) S(3):
…
3.668 A, S(1) S(1): 3.330 A, C(14)–H S(2): 2.960 A, C(15)–
…
˚
˚
˚
…
˚
H
S(2): 2.903 A]. These observations are qualitatively in
agreement with the results of Whangbo et al.30 on BEDT-TTF
and BEDO-TTF. As a matter of fact, the molecule that is the
most isolated in the solid state (Ie) exhibits the most planar
configuration.
Another difference between Ie on the one hand and Id and Ic
on the other hand is the position of the oxygen atom O(2)
which is located on the same side as C(15) with regard to the
…
C(6) O(1) axis of Ie and located on the side opposite to C(15)
for Id and Ic.
Fig. 2 Crystal structure of Ie. In this and subsequent figures
hydrogen atoms are omitted for clarity.
The charge transfer complex (Ic)2–TCNQ
content of three unit cells piled up along the [010] axis has been
drawn.24 In the donor stacks the intermolecular distance
defined as the distance between the mean planes through atoms
In the crystal, the donor and the acceptor entities pile up
separately. Within a stack adjacent entities are related by the
˚
crystallographic translation b ~ 4.052 A thus forming a regular
stacking pattern. This feature is illustrated in Fig. 6 where the
˚
S(1), S(2), S(3), S(4), C(3), C(4) is 3.72 A and the overlapping
3 5 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 5 1 – 3 5 6

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Fig. 6 Crystal structure of (Ic)2–TCNQ. The picture is a projection
down the [010] axis, tilted by about ten degrees to emphasize the
stacking. The content of three unit cells piled up along the [010] axis has
been drawn.
Fig. 3 Crystal structure of Id.
mode of the TTF cores is of the bond-over-ring type (Fig. 7a).
˚
In the acceptor stacks the intermolecular distance is 3.46 A but
the molecules are offset in such a way that the rings do not
overlap (Fig. 7b). Thus, it is likely that the TCNQ entities do
not much participate much in the conduction process. However
the segregated regular stacks and the overlapping mode of the
donor entities are favourable structural features for the setting
of a conduction path, provided that the donor has been
partially oxidized. As a matter of fact the conductivity of (Ic)2–
TCNQ measured on compressed pellets is relatively high
(sRT ~ 0.5 S cm21). As, in addition, no chalcogen chalcogen
…
short contact is observed between stacks, we can expect that
(Ic)2–TCNQ would display pure 1D transport properties.
Unfortunately the poor accuracy of the structure determina-
tion prevented us running band structure calculations. The
charge transfer between Ic and TCNQ can be estimated by
using the criterion, based on the bond lengths in TCNQ,
developed by Flandrois and Chasseau.31 From this criterion, it
is deduced that the charge of TCNQ is close to 21 implying
that each Ic entity has a partial charge of 10.5. However this
result should only be considered as qualitative because of the
low accuracy of the structural parameters.
Fig. 4 Crystal structure of Ic.
In addition, it is interesting to compare the shape of the
oxidized form of Ic to that of the neutral one (Fig. 5). The
oxidized molecule is close to planarity (ethylene and acetoxy-
phenyl groups excluded): the characteristic folding angles (as
Fig. 7 [a] Overlapping mode of the Ic entities; projection onto the
plane of the TTF core. [b] Overlapping mode of the TCNQ entities,
projection onto the molecular plane.
Fig. 5 Side view of the donor molecules. [a]: Ie; [b]: Id; [c]: Ic; [d]: Ic in
(Ic)2–TCNQ. In all these pictures the methyl carbon atom C(15) is
directed towards the reader.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 5 1 – 3 5 6
3 5 5

View Article Online
E. Canadell, P. Auban-Senzier and D. Je´rome, Chem. Mater.,
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J.-P. Legros, F. Dahan, L. Binet, C. Carcel and J.-M. Fabre,
J. Mater. Chem., 2000, 10, 2685.
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C. U. Pittman, M. Ueda and Y. F. Liang, J. Org. Chem., 1978, 44,
3639.
defined above) are a1 ~ 25.3u and a2 ~ 25.4u, to be compared
with 121.2u and 119.5u respectively in neutral Ic. It has often
been observed in other cases of TTF derivatives, that when the
neutral donor is folded, its oxidized form is planar. Another
strong difference between the two forms lies in the position of
the ethylene group with respect to the plane defined by atoms
S(1), S(2), C(1), C(2), Se(1), Se(2): keeping the same orientation
for the molecule in the neutral form, i.e. C(15) directed towards
the reader, the ethylene group is below this plane and in the
oxidized form it is above this plane (Fig. 5c and 5d). There is no
obvious reason other than weak intermolecular interactions (as
discussed above) to explain this inversion in conformation.
7
8
9
10 J.-M. Fabre, D. Serhani, K. Saoud and A. K. Gouasmia, Bull. Soc.
Chim. Belg., 1993, 102, 615.
11 M. R. Bryce, W. Devonport, L. M. Goldenberg and C. Wang,
Chem. Commun., 1998, 945.
12 M. R. Bryce, G. Cooke, W. Devonport, F. M. A. Duclairoir and
V. M. Rotello, Tetrahedron Lett., 2001, 42, 4223.
13 K. Ishikawa, K. Akiba and N. Inamoto, Tetrahedron Lett., 1976,
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14 C. Gonnella and M. P. Cava, J. Org. Chem., 1978, 43, 369.
15 M. Sato, N. C. Gonella and M. P. Cava, J. Org. Chem., 1979, 44,
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16 I. V. Sudmale, G. V. Tormos, V. Y. Khodorkovsky, A. S. Edzina,
O. J. Neilands and M. P. Cava, J. Org. Chem., 1993, 58, 1355.
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18 M. R. Bryce, M. A. Coffin and W. Clegg, J. Org. Chem., 1992, 57,
1696.
19 A. K. Gouasmia, J.-M. Fabre, L. Boudiba, L. Kaboub and
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20 L. B. Coleman, Rev. Sci. Instrum., 1975, 46, 1125.
21 L. J. Farrugia, WinGX, J. Appl. Cryst., 1999, 32, 837.
22 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori and M. Camalli, SIR92, a program for
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23 G. M. Sheldrick, SHELX97. Programs for crystal structures
analysis, Univesity of Go¨ttingen, Go¨ttingen, Germany, 1997.
24 3D files of Figs. 2, 3, 4 and 6 and Table 6 have been deposited with
the Electronic Supplementary Information (ESI) service.
25 H. Kobayashi, A. Kobayashi, Y. Sasaki, G. Saito and H. Inokuchi,
Bull. Chem. Soc. Jpn., 1986, 59, 301.
Conclusion
In this series of new compounds, it has been found that a donor
such as Ic could lead to a conducting TCNQ complex in spite of
its bent conformation in the neutral form. From this result we
hope to obtain improved electrical properties in salts of the
phenylhydroxylated derivative of Ic (or other type I com-
pounds) in which the occurrence of hydrogen bonds favours a
two dimensional character. The conversion of compounds Ia–
Id to the phenylhydroxylated species9,10 and the synthesis of
their radical cation salts and charge transfer complexes is now
under way.
Acknowledgements
This work was achieved within the framework of a ‘‘Franco-
Algerian inter-university cooperation programme’’ with the
support of the CMEP, the Algerian Ministry of Education and
the French Ministry of the Foreign Affairs and we warmly
thank these organisations. We also thank Dr Lydie Valade for
his constant support and fruitful discussions.
26 T. Suzuki, H. Yamochi, G. Srdanov, K. Hinkelmann and F. Wudl,
J. Am. Chem. Soc., 1989, 111(8), 3108.
27 (a) B. Garreau, B. Pomare`de, C. Faulmann, J.-M. Fabre,
P. Cassoux and J.-P. Legros, C. R. Acad. Sci., Se´r. II, 1991,
509; (b) B. Garreau, D. de Montauzon, P. Cassoux, J.-P. Legros,
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28 A. J. Moore, M. R. Bryce, G. Cooke, G. J. Marshallsay,
P. Skabara, A. S. Batsanov, J. A. K. Howard and T. A. K. Daley,
J. Chem. Soc., Perkin Trans. 1, 1993, 1403.
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