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

In the title compound, C14H13ClN+·C6H4BrO3S−, the cation exists in an E configuration with respect to the ethenyl bond and is almost planar, the dihedral angle between the pyridinium and the benzene rings being 2.80 (7)°. The dihedral angles between the benzene ring of the anion and the pyridinium and benzene rings of the cation are 80.88 (7) and 79.05 (7)°, respectively. In the crystal, the cations are stacked into columns along the a axis as a result of π–π interactions between the pyridinium and chlorobenzene rings with a Cg⋯Cg distance of 3.6976 (8) Å. The anions are linked into chains along the a axis by weak C—H⋯O interactions. These anion chains are linked to adjacent cations by additional weak C—H⋯O and C—H⋯Br interactions, forming a two-dimensional network parallel to the ab plane. There are also short O⋯Br [3.2567 (11) Å] and C⋯O [2.9917 (18) Å] contacts. The crystal structure is further stabilized by C—H⋯π interactions involving the aromatic ring of the anion.


Comment
Stilbazolium is a competitive candidate for organic nonlinear optical (NLO) materials and yields high optical nonlinearities including large second harmonic generation (SHG) (Andreu et al., 1999;Jagannathan et al., 2007). Molecules with large π systems have been extensively used in attempts to obtain NLO materials (Veiros, 2001). This hypothesis led to a popular approach towards such materials which are synthesized from compounds with extended π conjugated systems to ensure large second-molecular hyperpolarizability (β) (Lakshmanaperumal et al., 2003). However, this approach will not be effective if the molecules of these compounds are arranged in centrosymmetric space groups (Cho et al., 2002). The title compound (I) has been synthesized and its crystal structure was undertaken in order to establish the orientation of molecules in the solid state. It was found that (I) crystallized in centrosymmetric space group P2 1 /c so no second-order nonlinear optical properties are observed.
In the molecule of the title compound, C 14 H 13 ClN + . C 6 H 4 BrO 3 S - (Fig. 1), the cation exists in an E configuration with respect to the ethenyl C6═C7 bond [1.3393 (19) Å] and the torsion angle of C5-C6-C7-C8 = 178.74 (14)°. The cation is almost planar with the dihedral angle between the pyridinium and benzene rings of the cation being 2.80 (7)°. The anion is inclined 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 80.88 (7) and 79.05 (7)°. The Br substituents are coplanar with the attached benzene rings.
The bond distances in both cation and anion have normal values (Allen et al., 1987) and are comparable with the closely related compounds (Chanawanno et al., 2008;2009;Chantrapromma et al., 2006;Fun 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).
Brown 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 month, Mp. 508-509 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 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 0.70 Å from Cl1 and the deepest hole is located at 0.50 Å from Cl1. 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. O2-S1-O1 113.69 (7) C11-C10-C9 118.67 (13) O2-S1-O3 113.19 (7) C11-C10-H10A 120.7 O1-S1-O3 112.92 (7) C9-C10-H10A 120.7 O2-S1-C15