(E)-4-[4-(Dimethylamino)styryl]-1-methylpyridinium 4-bromobenzenesulfonate1

In the title compound, C16H19N2 +·C6H4BrO3S−, the cation is nearly planar, with a dihedral angle of 3.19 (15)° between the pyridinium and the dimethylaminophenyl rings, and exists in the trans configuration. In the crystal packing, the cations and anions are linked into chains parallel to the c axis. These chains are stacked along the b axis. The crystal is stabilized by weak C—H⋯O and C—H⋯π interactions, and a π–π interaction is also observed with a Cg⋯Cg distance of 3.5675 (19) Å.

Previous studies (Dittrich et al., 2003;Nogi et al., 2000;Sato et al., 1999) have shown that DAST and its analogues exhibit second-order non-linear optical properties. To investigate the effect of counter anion on the NLO properties of DAST, the title compound was prepared by changing the counter anion from 4-toluenesulfonate in DAST to 4-bromobenzenesulfonate.
The title compound is found to crystallize with the non-centrosymmetric space group Cc and therefore has second order nonlinear optical properties.
The asymmetric unit of the title compound ( Fig. 1) et al., 1987) and the cation bond lengths and angles are comparable with related structures (Chantrapromma et al., 2008).
Experimental Mp. 536-537 K). Silver(I) p-bromobenzenesulfonate (compound B) was synthesized according to our previously reported procedure (Chantrapromma et al., 2006). The title compound was synthesized by mixing compound A (0.20 g, 0.5 mmol) in hot methanol (25 ml) and a solution of compound B (0.17 g, 0.5 mmol) in hot methanol (50 ml). The mixture immediately yielded a grey precipitate of silver iodide. After stirring the mixture for 30 min, the precipitate of silver iodide was removed supplementary materials sup-2 and the resulting solution was evaporated yielding a red solid. Red plate-shaped single crystals of the title compound suitable for x-ray structure determination were recrystalized from methanol by slow evaporation of the solvent at room temperature over several days, Mp. 536-537 K.

Refinement
All H atoms were placed in calculated positions with d(C-H) = 0.93 Å, U iso =1.2U eq (C) for aromatic and CH, 0.96 Å, U iso = 1.5U eq (C) for CH 3 atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.47 Å from Br1 and the deepest hole is located at 0.71 Å from Br1. A total of 1997 Friedel pairs were used to determine the absolute structure.
Figures Fig. 1. The asymmetric unit showing 50% probability displacement ellipsoids and the atomnumbering scheme.