Experimental

In the title compound, C12H12NS+·C7H7O3S−, the cation exists in an E configuration with respect to the ethenyl C=C bond. The cation is essentially planar with a dihedral angle of 1.94 (10)° between the pyridinium and thiophene rings. The benzene ring of the anion makes dihedral angles of 75.23 (10) and 76.83 (10)°, respectively, with the pyridinium and thiophene rings. In the crystal structure, cations and anions form alternate layers parallel to the bc plane. Within each layer, both cations and anions are arranged into chains directed along the b axis. The cation chain and the anion chain are interconnected by weak C—H⋯O interactions into a three-dimensional network. The crystal structure is further stabilized by C—H⋯π interactions.

In the title compound, C 12 H 12 NS + ÁC 7 H 7 O 3 S À , the cation exists in an E configuration with respect to the ethenyl C C bond. The cation is essentially planar with a dihedral angle of 1.94 (10) between the pyridinium and thiophene rings. The benzene ring of the anion makes dihedral angles of 75.23 (10) and 76.83 (10) , respectively, with the pyridinium and thiophene rings. In the crystal structure, cations and anions form alternate layers parallel to the bc plane. Within each layer, both cations and anions are arranged into chains directed along the b axis. The cation chain and the anion chain are interconnected by weak C-HÁ Á ÁO interactions into a threedimensional network. The crystal structure is further stabilized by C-HÁ Á Á interactions.

Comment
Pyridinium derivatives have been found to have nonlinear optical properties (Lakshmanaperumal et al., 2002(Lakshmanaperumal et al., , 2004Usman et al., 2000Usman et al., , 2001. We have previously synthesized and crystallized several compounds of pyridinium and quinolinium derivatives to study their non-linear optical properties Chantrapromma, Jindawong, Fun & Patil, 2007;Chantrapromma et al., 2008;Ruanwas et al., 2008). As part of our research on nonlinear optic materials, the title compound was synthesized.
All the O atoms of 4-methylbenzenesulfonate anion are involved in the C-H···O weak interactions (Table 1). In the crystal packing (Fig. 2), the cations and anions form alternate layers parallel to the bc plane. Within each layer both cations and anions are arranged into chains directed along the b axis. The cations and anions chains are interconnected by C-H···O weak interactions into a three dimensional network. The crystal structure is further stabilized by the C4-H4A···π and C10-H10A···π interactions (Table 1); Cg 1 is the centroid of the C13-C18 benzene ring.

Experimental
The title compound was synthesized by mixing 4-(2-thiophenestyryl)-1-methylpyridinium iodide (0.1 g, 0.3 mmol) which was prepared in a similar manner to that previously reported  in hot methanol (40 ml) and p-toluenesulfonate (0.09 g, 0.3 mmol) in hot methanol (30 ml) (Rahman et al., 2003). The mixture immediately yielded a yellow solid of silver iodide. After stirring the mixture for 30 min, the precipitate of silver iodide was removed and the resulting solution was evaporated and the green-yellow solid was obtained. Yellow block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystalized from the methanol/ethanol (1:1 v/v) solvent by slow evaporation of the solvent at room temperature after several weeks (m.p. 507-509 K).
supplementary materials sup-2 Refinement All H atoms could have been discerned in a difference Fourier map. Nevertheless, all the H atoms attached to the carbon atoms were constrained in a riding motion approximation with C aryl -H = 0.93 and C methyl -H = 0.96 Å. 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 1.01 Å from C6 and the deepest hole is located at 0.33 Å from S1. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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 > σ(F 2 ) is used only for calculating Rfactors(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.