(E)-2-Cyano-3-(2,3-dimethoxyphenyl)acrylic acid

The asymmetric unit of the title compound, C12H11NO4, contains two molecules. In the crystal, neighbouring molecules are linked together by O—H⋯O hydrogen bonds into dimers. The dimers are arranged into columns parallel to the a axis, meditated by π–π interactions [centroid–centroid distances = 3.856 (3) and 3.857 (3) Å]. The crystal structure is further stabilized by weak intermolecular C—H⋯O interactions. The crystal studied was a non-merohedral twin with a ratio of the twin components of 0.657 (11):0.343 (11).

The asymmetric unit of the title compound, C 12 H 11 NO 4 , contains two molecules. In the crystal, neighbouring molecules are linked together by O-HÁ Á ÁO hydrogen bonds into dimers. The dimers are arranged into columns parallel to the a axis, meditated byinteractions [centroid-centroid distances = 3.856 (3) and 3.857 (3) Å ]. The crystal structure is further stabilized by weak intermolecular C-HÁ Á ÁO interactions. The crystal studied was a non-merohedral twin with a ratio of the twin components of 0.657 (11):0.343 (11). H atoms treated by a mixture of independent and constrained refinement Á max = 0.23 e Å À3 Á min = À0.23 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).  (Zhao et al., 2008;Wang et al., 2009). Transition metal complexes with these ligands have special properties and applications (Mitra et al., 2006;Shit et al., 2009;Akhbari et al., 2009;). Among the carboxylate compounds, cyanoacrylic acid derivatives are of great importance to convert solar light into electricity in dye-sensitized solar cells (Hagberg et al., 2006;Kim et al., 2008 andHara et al., 2003).

Related literature
In consideration of the important applications of carboxylate compounds, herein the crystal structure of the title compound, (I), is reported. Systematic characterization of (I) has been performed by elemental analyses, FT-IR, 1 H-NMR,

UV-Vis spectroscopy and x-ray crystallography
The molecular structure of (I) with the atom-numbering scheme is presented in Fig. 1. The asymmetric unit of (I) contains two molecules, which differ mainly in the orientation of methoxy groups (Fig. 3) as reflected in the C1-C2-O3-C11 and C13-C14-O7-C23 torsion angles of -120.5 (7)° and 121.0 (7) °, respectively. In both molecules, the phenyl ring and the chain connecting the ring to the CN and COOH groups are nearly coplanar. The dihedral angles between the planes of the phenyl rings (C1-C6, C13-C18) and the planes defined by C7-C10 and C19-C22, are 5.7 (4)° and 5.5 (4) °, respectively. This degree of coplanarity allows for increased π-conjugation in the title compound.
Careful inspection of the packing diagram ( Fig. 2) lead us to assumption that the two independent molecules could be related by non-crystallographic inversion center. To test this assumption, we used in the first step a rigid-body approach available in the crystallographic package JANA2006 (Petříček et al., 2006). The atoms of the first molecule (C1-C12, N1, O1-O4) were taken as a model molecule and refined to obtain the geometry of the model molecule. Together with the model molecule we refined a translation vector and three rotation angles transforming the model molecule to the actual position A (C1-C12, N1, O1-O4) and another translation vector and three rotation angles transforming the inverted model molecule to the actual position B (C13-C24, N2, O5-O7). The resulting R value was 5.2% for 164 refined parameters, providing evidence that the geometry of A and inverted geometry of B can be considered identical. In the second step, we graphically connected corresponding atoms in the two identical molecules A and B by lines (Fig. 4) to inspect visually position of the possible non-crystallographic inversion centre. The lines did not intersect at the same point but the obtained intersections were very close indicating that the inversion center is present only approximately. In order to quantify this finding in terms of R value we used the original structure model without rigid body (i.e. the one reported in this article) and we restricted the coordinates and ADP parameters of corresponding atoms of the two molecules by a local inversion symmetry operation located at the average position of the intersections shown in Fig. 4. Indeed, the resulting R value increased to 7.1% for 158 refined parameters.
In the crystal, the molecules form hydrogen-bonded dimers via the carboxyl groups. These dimers are connected by π-π interactions (centroid-centroid distances 3.856 (3), 3.857 (3) Å into columns parallel to the a axis (Fig. 2). The crystal structure is further stabilized by weak intermolecular C-H···O interactions.
supplementary materials sup-2 The crystal studied was a non-merohedral twin with the ratio of the twin components of 0.657 (11):0.343 (11).
Experimental 2,3-dimethoxybenzaldehyde (0.4 mmol) and cyanoacetic acid (0.4 mmol) were dissolved in a mixture of methanol:acetonitrile (1:1 v/v, 20 ml) in the presence of piperidine (0.4 mmol). The mixture was stirred and refluxed for 1.5 h to give a clear yellow solution. The mixture was cooled and the product was allowed to crystallize by slow evaporation technique at room temperature. After 5 days, yellow precipitate of (I) was formed which was collected by filtration and dried at room temperature. Recrystallization of the yellow precipitate from acetonitrile-chloroform mixture (2:1 v/v, 30 ml) by adding acetic acid afforded yellow crystals of 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid (1). Yield: 91%. Anal.

Refinement
All H atoms bonded to carbon atoms were positioned geometrically and treated as riding on their parent atoms. The methyl H atoms were allowed to rotate freely about the adjacent C-O bonds. The carboxyl H atoms were found in difference Fourier maps and their coordinates were refined with restraint on the O-H bond length 0.85 Å with σ of 0.02. All H atoms were refined with displacement coefficients U iso (H) set to 1.5U eq (C, O) for the methyl and carboxyl groups and to to 1.2U eq (C) for the CH-groups. As the structure contains only light atoms, Friedel pairs were merged and the Flack parameter value has not been determined.
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.
The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.
supplementary materials sup-5 The crystal studied was a non-merohedral twin with a minor twin domain of 24.7 (8)%. The overlaps of reflection between the twin domains were calculated by Jana2006 software using the twinning matrix and user-defined thresholds 0.23° for full overlap and 0.35°f or full separation. For fully overlapped reflections, only a partial F 2 , corresponding to the twin volume fraction, were used in the refinement. Partially overlapped reflections were discarded from the refinement.