1-Methyl-4-[(E)-2-(2-thienyl)ethenyl]pyridinium 4-chlorobenzenesulfonate1

In the title compound, C12H12NS+·C6H4ClO3S−, the cation is almost planar and exists in the E configuration. The cations and anions form alternate layers parallel to the ab plane. Within each layer, both cations and anions form chains directed along the b axis. The molecules are interconnected by weak C—H⋯O interactions into a three-dimensional network. The crystal structure is further stabilized by C—H⋯π interactions involving the thiophene ring. The sulfonate and thiophene groups are involved in weak intramolecular C—H⋯O and C—H⋯S interactions, respectively. The latter intramolecular hydrogen bonds produce S(5) ring motifs.


Comment
Molecules with extended π systems have been extensively used in attempts to obtain materials with non-linear optical (NLO) properties. Organic crystal with the required conjugated π electrons are attractive candidates because of the large NLO coefficients. In our research for second-order NLO materials, we have previously synthesized and crystallized several organic ionic salts of pyridinium and quinolinium derivatives to study their non-linear optical properties 2006a;2006b;2007a;2007b;2007c;2007 d;Jindawong et al., 2005). An earlier study carried out by Drost et al. (1995) has revealed that the products of the dipole moment and the molecular hyperpolarizability (β) of thiophenecontaining conjugated moieties are larger than those of the phenyl analogues. Based on this reason, we have synthesized the title compound which was designed by replacement of the cationic phenyl ring by the thiophene ring that is present in 4-(4'-Hydroxy-3'-methoxystyryl)-1-methylpyridinium 4-chlorobenzenesulfonate .
The asymmetric unit of the title compound consists of the C 12 H 12 NS + cation and the C 6 H 4 ClO 3 S − anion. The cation is almost planar and exists in the E configuration with respect to the C6═C7 double bond [1.334 (3) Å]. The cation is almost perpendicular to the anion as is indicated by the angles between the mean planes of the chlorophenyl ring to the pyridinium as well as to the thiophene ring being 87.64 (9)° and 86.73 (9)°, respectively. The dihedral angle between the pyridinium and the thiophene rings is 5.74 (10)°. The ethenyl unit is nearly planar. The torsion angles C4-C5-C6-C7 = −4.3 (3)° and C6-C7-C8-S1 = −1.5 (3)°.
The atom O3 of the sulfonate and the S atom of the thiophene contribute to the C-H···O and C-H···S intramolecular weak interactions ( Fig. 1 and Table 1) forming S(5) ring motifs (Bernstein et al., 1995). The bond lengths and angles are normal (Allen et al., 1987) and are comparable with closely related structures 2006b;2007c;2007 d).
All the O atoms of 4-chlorobenzenesulfonate anion are involved in the C-H···O weak interactions (Table 1). The cations and anions form alternate layers parallel to the ab plane. Within each respective layer, the ions are interconnected by C-H···O weak interactions and in each respective layer can be distinguished chains directed along the b axis.
The alternating layers are separated by 4.282 (2) Å and are further linked into a three dimensional network by C-H···O weak interactions (Table 1). The sulfonate as well as the thiophene are involved in C-H···O and C-H···S intramolecular weak interactions, respectively. These weak hydrogen bonds participate in S(5) ring motifs. The crystal structure is further stabilized by the C12-H12B···π interaction to the thiophene ring C8-C11/S1: C12-H12B=0.96; H12B···Cg1 i =2.692; C12-Cg1 i =3.515 (2) Å; C12-H12B···Cg1 i = 144°. [Cg1 i is the centroid of the S1/C8-C11 thiophene ring (symmetry code: A very interesting feature is the short non-bonding contact between Cl1 and O3 that is 2.963 (1) Å long only. A search in the Cambridge Structural Database (version 5.29 and addenda up to 25-th January 2008; Allen, 2002) among the structures which have been flagged with no error or disorder as well as with R-factor < 0.05 and which contained chloro-phenyl with supplementary materials sup-2 any substituent in the para position showed that the present structure contains an unprecedentedly short contact of this kind.
Experimental 4-(2-Thiophenestyryl)-1-methylpyridinium iodide (compound A) was synthesized by mixing a solution (1:1:1 molar ratio) of 1,4-dimethylpyridinium iodide (2.00 g, 8.5 mmol), 2-thiophenecarboxaldehyde (6.00 ml, 8.5 mmol) and piperidine (0.84 ml, 8.5 mmol) in hot methanol (40 ml). The resulting solution was refluxed for 5 h under a nitrogen atmosphere. The resultant solid was filtered off, washed with diethyl ether and recrystallized from methanol. The title compound was synthesized by mixing compound A (0.10 g, 0.3 mmol) in hot methanol (20 ml) and silver(I) 4-chlorobenzenesulfonate (0.08 g, 0.3 mmol) in hot methanol (30 ml). Silver(I) 4-chlorobenzenesulfonate was synthesized according to our previously reported procedure (Chantrapromma et al., 2006b). The mixture immediately yielded a grey solid of silver iodide. After stirring the mixture for ca 30 min, the precipitate of silver iodide was removed and the resulting solution was evaporated and a brown solid was obtained. Brown block-shaped single crystals of the title compound suitable for x-ray structure determination were recrystalized from methanol solvent by slow evaporation of the solvent at room temperature after several days (Mp.

Refinement
All the hydrogen atoms could have been discerned in the 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=0.968 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 0.75 Å from C8 and the deepest hole is located at 0.50 Å from S1.   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.