(E)-2-[4-(Dimethylamino)styryl]-1-methylpyridinium 4-methylbenzenesulfonate monohydrate

The cation of the title compound, C16H19N2 +·C7H7O3S−·H2O, exists in the E configuration with respect to the C=C double bond and is essentially planar, the dihedral angle between the pyridinium and benzene rings being 3.55 (13)°. In the crystal, π-conjugated planes of cations and anions are inclined to each other at 84.30 (11)°. The crystal structure is stabilized by O—H⋯O hydrogen bonds and weak C—H⋯O interactions, which link the cations, anions and water molecules into chains along the b axis. These chains are stacked along the a axis by π–π interactions with centroid–centroid distances of 3.6032 (16) and 3.6462 (16) Å.


Comment
Quarternary ammonium compounds and sulfonamide drugs are the interesting antibacterial agents. They are widely used in industrial disinfection and hospital treatment (Barlow et al., 1937;Ohkura et al., 2003). Pyridinium derivatives represent a class of synthetic quarternary ammonium compounds that show significant antibacterial activity. (Pernak et al., 2001).
The title compound was synthesized based on the combination of pyridinium and sulfonamide chemophores in order to yield a potent disinfectant. Our biological actvity results showed that the title compound was moderately active against Gram-positive bacteria ie Methicillin-Resistant Staphylococcus aureus with the MIC = 37.5 µg/ml. However it was inactive against the Gram-negative bacteria we tested which are Pseudomonas aeruginosa, Salmonella typhi and Shigella sonnei (Chanawanno et al., 2010). Herein its crystal structure is reported. The cation is essentially planar with the dihedral angle between the pyridinium and the dimethylaminophenyl rings being 3.55 (13)° and with the torsion angle C5-C6-C7-C8 = 176.3 (3)°. Both methyl groups of dimethylamino moiety are slightly twisted from the mean plane of the attached C8-C13 ring as indicated by the torsion angles C15-N2-C11-C10 = 9.3 (4)°a nd C16-N2-C11-C12 = 3.5 (4)°. The relative arrangement of cation and anion is shown by the interplanar angle between the mean plane of the π-conjugate system (C1-C13/N1) of the cation and the C17-C22 benzene ring of the anion being 84.30 (11)°. The bond lengths (Allen et al., 1987) and angles in (I) are in normal ranges and comparable with a related structure (Kobkeatthawin et al., 2009).
In the crystal packing, all O atoms of the sulfonate group are involved in weak C-H···O interactions ( Table 1). The cation is linked to both the anion and water molecule by weak C-H···O interactions, and the anion is linked to the water molecule by O-H···O hydrogen bond. These three molecules are linked into chains along the b axis (Table 1, Fig. 2). These chains are stacked along the a axis ( Fig. 2) by π-π interactions with the distances Cg 1 ···Cg 1 = 3.6032 (16) Å (symmetry code: 2 -x, 2 -y, -z) and Cg 1 ···Cg 2 = 3.6462 (16) Å (symmetry code: 1 -x, y, z); Cg 1 and Cg 2 are the centroids of the N1/C1-C5 and C8-C13 rings, respectively.

Experimental
The title compound was prepared by the reported procedure (Chanawanno et al., 2010). Orange needle-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 after a few weeks. Mp. 468-469 K.

Refinement
Water H atoms were located in difference maps and refined isotropically. The remaining H atoms were placed in calculated positions with d(C-H) = 0.93 Å, U iso =1.2U eq (C) for aromatic and CH and 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 1.08 Å from O1 and the deepest hole is located at 0.85 Å from S1.
Figures Fig. 1. The asymmetric unit of (I) showing 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. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1