organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
two samples were the same and agreed with previously
reported data (Sankaran & Reynolds, 1997). The stark
contrast in crystal morphology and color, yet similar NMR
properties, piqued our interest in determining the crystal
structure of the unexpected product.
ISSN 0108-2701
A substituted EDOT precursor:
diethyl 3,4-dihydroxythiophene-
2,5-dicarboxylate
Christophe Faulmanna* and Anthony E. Pullenb
The asymmetric unit of the title compound contains two
independent molecules, named hereafter as A and B (Fig. 1),
which lie almost in the same plane, close to (101). The planes
of molecules A and B form an angle of ꢀ1.52 (4)ꢁ. Compar-
ison of intramolecular bond lengths (Table 1) and angles does
not show any discrepancies between units A and B. For each
type of bond, distances are very homogeneous, except for one
methyl group (see below). The only structural difference
between these two units is the conformation of one of the
terminal methyl groups. In molecule A, the methyl group that
involves atom C7 points out of the plane of the molecule [C7
aLaboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne,
31077 Toulouse Cedex, France, and bA123Systems, 8 Saint Mary's Street,
Boston, MA 02215, USA
Correspondence e-mail: faulmann@lcc-toulouse.fr
Received 17 February 2004
Accepted 22 March 2004
Online 21 April 2004
The title compound, C10H12O6S, has been obtained as dark-
yellow chunk-shaped crystals, together with the expected thin
white needles. The structures of the two phases are identical.
Two independent molecules compose the asymmetric unit:
one molecule is totally planar, whereas a methyl group of the
second molecule points out of the plane. Each molecule
participates in several intra- and intermolecular hydrogen
bonds and short contacts. The overall structure can be
regarded as parallel sheets of molecules. Within a sheet,
molecules are connected to one another in an in®nite network
via numerous short intermolecular contacts. Sheets are
connected via hydrogen bonds and short contacts, in particular
involving the methyl groups.
Ê
lies 1.128 (3) A from the molecular plane], whereas molecule
Ê
B is almost planar [the largest deviation is 0.164 (1) A for
atom O15].
The result of this non-planarity in molecule A is the exis-
tence of one short intermolecular contact, which can be
regarded as a potential hydrogen bond between A and B via
atoms C7, H71 and O12(1 x, 1 y, 2 z) (see Table 2). As
a result of these short contacts, the CÐH bond lengths around
Ê
atom C7 [mean distance = 1.02 (4) A] are slightly larger than
Ê
those of the other methyl groups [mean distance = 0.96 (4) A].
Atom C17 is also involved in a short intermolecular contact
with atoms O5(2 x, 1 y, 1 z) and H173 [CÐH =
Comment
Electrically conducting polymers are a widely and intensively
researched class of materials in both industry and academia
(Skotheim et al., 1998). One particular family of conducting
polymers, namely poly(ethylenedioxythiophenes) (PEDOTs),
have shown extraordinary promise in a variety of applications
because of their low oxidation potentials, high conductivity,
oxidation-state stability and thin-®lm transparency (Groe-
nendaal et al., 2003). Several commercially available products
use a PEDOT-based material (Groenendaal et al., 2000).
Utilizing the electronic properties of PEDOTs, which are
superior to those of other conducting polymer systems, we set
out to design and synthesize substituted PEDOT-based poly-
mers.
According to previously reported procedures, PEDOTs can
be readily derivatized at the ethylenedioxy bridge (Sankaran
& Reynolds, 1997; Lima et al., 1998). During puri®cation of the
substituted EDOT precursor diethyl 3,4-dihydroxythiophene-
2,5-dicarboxylate, (II), which was prepared from the diethyl
thiodiglycolate, (I), in two steps, unexpected dark-yellow
chunk-like crystals formed alongside the expected and
previously reported white needles. The 1H NMR data for the
Figure 1
The molecular structure of (II), with 50% probability displacement
ellipsoids (top: projection on to the plane of the molecules; bottom: side
view of the molecules). Hydrogen bonds are represented by dashed lines.
o338 # 2004 International Union of Crystallography
DOI: 10.1107/S0108270104006754
Acta Cryst. (2004). C60, o338±o340