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

In the title salt, C14H13ClN+·C6H4ClO3S−, the cation exists in an E configuration with respect to the ethynyl bond and is approximately planar, with a dihedral angle of 3.4 (2)° between the pyridinium and benzene rings. The anion is approximately perpendicular to the cation plane, the benzene ring of the anion making dihedral angles of 89.4 (2) and 89.9 (2)°, respectively, with the pyridinium and benzene rings of the cation. In the crystal structure, the cations are linked into a chain along the c axis by C—H⋯Cl interactions. The anions are linked to the adjacent cation chains by C—H⋯O and C—H⋯Cl interactions, forming a two-dimensional network parallel to the bc plane. The crystal structure is further stabilized by C—H⋯π interactions. A π–π interaction is also observed between the pyridinium ring and the benzene ring of the cation with a centroid–centroid distance of 3.668 (3) Å.


Comment
To search for new materials capable for nonlinear optical (NLO) applications, many studies have focused on organic molecules containing highly polarizable π-conjugated backbones (Wenseleers et al., 1998). For second order NLO compounds, an electron donor and an acceptor group are attached to both ends of this backbone to create an asymmetric "push-pull" system (Prasad & Williams, 1991). In addition, due to the inherently second-order NLO character of noncentrosymmetric organic compounds, the x-ray structure determination is a very important method to determine their NLO properties (Koshima & Matsuura, 1998). 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 et al., 2007Chantrapromma et al., , 2008Chantrapromma, Chanawanno & Fun, 2009;Chantrapromma, Jansrisewangwong et al., 2009). The title compound (I) has been synthesized and its crystal structure was undertaken in order to establish the conformation of the various groups and its crystal packing. The title compound crystallized in centrosymmetric space group P2 1 /c which precluded the second-order nonlinear optical properties.
In the molecule of the title compound, C 14 H 13 ClN + .C 6 H 4 ClO 3 S - (Fig. 1), the cation exists in an E configuration with respect to the C6═C7 double bond [1.339 (7) Å] and the torsion angle of C5-C6-C7-C8 = 178.2 (4)°. The cation is almost planar with the dihedral angle between the pyridinium and benzene rings of the cation being 3.4 (2)°. The orientation of the anion is perpendicular with respect to the cation which is reflected by the dihedral angles between the benzene ring of the anion and the pyridinium and benzene rings of the cation being 89.4 (2)° and 89.9 (2)°. The Clions are coplanar with the attached benzene rings. The bond distances in both cation and anion have normal values (Allen et al., 1987) and comparable with the closely related compounds (Chanawanno et al., 2008;Chantrapromma et al., 2007Chantrapromma et al., , 2008Chantrapromma, Chanawanno & Fun, 2009;Chantrapromma, Jansrisewangwong et al., 2009).
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 individually arranged alternatively with the cations being linked into chains along the c axis by C-H···Cl weak interaction (Table 1). The anions are linked to the adjacent cations chains by C-H···O and C-H···Cl weak interactions forming a 2D network parallel to the bc plane. The crystal structure is further stabilized by C-H···π interactions (Table 1). A π-π interaction is also observed with the Cg 1 ···Cg 2 distance of 3.668 (3) Å (symmetry code: -x, 1-y, 1-z); Cg 1 , Cg 2 and Cg 3 are the centroids of C1-C5/N1, C8-C13 and C15-C20, respectively.
Experimental 2-[(E)-2-(4-Chlorophenyl)ethenyl]-1-methylpyridinium iodide (0.24 g, 0.67 mmol) which was prepared according to the previous report (Chanawanno et al., 2008) was mixed (1:1 molar ratio) with silver(I) 4-chlorobenzenesulfonate (0.20 g, 0.67 mmol) (Chantrapromma et al., 2007) 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 sup-2 orange solid. Orange needle-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. 485-487 K).

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 atoms. 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 0.91 Å from Cl1 and the deepest hole is located at 0.91 Å from S1. Fig. 1. The molecular structure of the title compound, with 50% 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.