2-[(E)-2-(4-Chlorophenyl)ethenyl]-1-methylpyridinium 4-methoxybenzenesulfonate

In the asymmetric unit of the title salt, C14H13ClN+·C7H7O4S−, there are two crystallographically independent molecules for each component. Each cation adopts an E configuration with respect to the C=C bond and is slightly twisted; the dihedral angle between the pyridinium and benzene rings is 6.53 (7)° for one molecule and 5.30 (7)° for the other. The methoxy groups in the anion molecules are each twisted from the mean plane of benzene ring with torsion angles of 16.38 (19) and 4.32 (19)°. In the crystal structure, the cations are stacked in an antiparallel manner along the a axis and the anions are linked together by C—H⋯O interactions into a layer parallel to (001). The anion layers are further linked to adjacent cations by C—H⋯O interactions. C—H⋯π interactions involving the benzene rings of both ions are also observed.

In the asymmetric unit of the title salt, C 14 H 13 ClN + ÁC 7 H 7 O 4 S À , there are two crystallographically independent molecules for each component. Each cation adopts an E configuration with respect to the C C bond and is slightly twisted; the dihedral angle between the pyridinium and benzene rings is 6.53 (7) for one molecule and 5.30 (7) for the other. The methoxy groups in the anion molecules are each twisted from the mean plane of benzene ring with torsion angles of 16.38 (19) and 4.32 (19) . In the crystal structure, the cations are stacked in an antiparallel manner along the a axis and the anions are linked together by C-HÁ Á ÁO interactions into a layer parallel to (001). The anion layers are further linked to adjacent cations by C-HÁ Á ÁO interactions. C-HÁ Á Á interactions involving the benzene rings of both ions are also observed.

Comment
In search for new organic nonlinear optical (NLO) materials, aromatic compounds with donor and acceptor substituents are extensively studied. Styryl pyridinium derivatives are considered to be promising NLO materials Cheng, Tam, Stevenson et al., 1991). During the course of our exploring for new organic NLO materials, we have previously synthesized and reported a number of the crystal structures of pyridinium derivatives (Chanawanno et al., 2008;Chantrapromma, Rodwatcharapiban & Fun, 2006;Chantrapromma, Ruanwas et al., 2006;Chantrapromma et al., 2009).
The title compound (I) has been synthesized and its crystal structure is reported here as part of our ongoing research on NLO materials. Unfortunately, the title compound crystallized in centrosymmetric space group P2 1 /c and does not exhibit second-order nonlinear optical properties.
In the crystal packing ( Fig. 2), all O atoms of the sulfonate group are involved in weak C-H···O interactions ( Table   1). The cations and anions are alternately arranged with the cations stacked in an antiparallel manner along the a axis and the anions linked together by C-H···O weak interactions (Table 1) into chains along the same direction. The anion chains are further linked to the adjacent cations into ribbons along the c axis by C-H···O weak interactions (Table 1). The crystal structure is further stabilized by C-H···π interactions involving the benzene rings (Table 1); Cg1, Cg2, Cg3 and Cg4 are the centroids of the C8A-C13A, C8B-C13B, C1A-C6A and C1B-C6B rings, respectively.
Experimental 2-[(E)-2-(4-chlorophenyl)ethenyl]-1-methylpyridinium iodide (0.24 g, 0.67 mmol) was prepared according to the previous report (Chanawanno et al., 2008) and mixed with silver(I) 4-methoxybenzenesulfonate (0.19 g, 0.67 mmol) (Chantrapromma, Rodwatcharapiban & Fun, 2006) in methanol solution (100 ml). The mixture solution was stirred for 30 min, the precipitate of silver iodide which formed was filtered and the filtrate was evaporated to give the title compound as an orange solid. Orange block-shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from methanol by slow evaporation at room temperature over a few weeks (m.p. 476-477 K).
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH, and 0.96 Å for CH 3 . The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.79 Å from Cl1A and the deepest hole is located at 0.61 Å from S1A. Fig. 1. The molecular structure of the title compound, with 40% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.