1-Methyl-4-[(E)-2-(3-hydroxy-4-methoxyphenyl)ethenyl]pyridinium 4-bromobenzenesulfonate monohydrate

In the title hydrated salt, C15H16NO2 +·C6H4BrO3S−·H2O, the cation exists in an E conformation with respect to the ethenyl bond and is almost planar, with a dihedral angle of 2.62 (12)° between the planes of the pyridinium and benzene rings. The methoxy substituent deviates slightly from the plane of its attached benzene ring [Cmethyl—O—C—C torsion angle = −11.6 (6)°]. In the crystal, the cations, anion and water molecules are linked together into chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O interactions. There is a short Br⋯O contact [3.029 (2) Å]. The crystal structure also features C—H⋯π interactions involving the benzene ring of the anion.


Comment
The stilbene scaffold is a basic element for a number of biologically active natural and synthetic compounds. Stilbenebased compounds are extensively present in nature and have attracted chemists and biologists because of their wide range of biological activities, acting as antibacterial (Chanawanno et al., 2010), anticancer (Belluti et al., 2010) and antioxidant (Frombaum et al., 2012) agents. In addition, some stilbenes also exhibit non-linear optical (Ruanwas et al., 2010) and fluorescent properties (Li et al., 2013). They are also generally used in the manufacturing industry as whitening agents (Hussain et al., 2009). Due to these interesting properties, the title pyridinium-stilbene (I) was synthesized. We report herein the synthesis and crystal structure of (I).
The asymmetric unit of (I) consists of a C 15 H 16 NO 2 + cation, a C 6 H 4 BrSO 3anion and a H 2 O molecule (Fig. 1). All bond lengths (Allen et al., 1987) and angles in both the cation and anion are normal and compare well with those found in closely related structures (Chanawanno et al., 2009;Fun et al., 2011;Jindawong et al., 2005). The cation exists in an E configuration with respect to the C13 ═C14 double bond [1.326 (5) Å] and the C12-C13-C14-C15 torsion angle is 179.3 (3)°. The cation is essentially planar with a dihedral angle between the pyridinium and benzene rings of the cation of 2.62 (12)°. The hydroxy group lies close to the plane of the C7···C12 benzene ring whereas the methoxy group is slightly twisted from this plane with a C21-O5-C9-C10 torsion angle of -11.6 (6)°. The benzene ring of the 4-bromobenzenesulfonate anion makes dihedral angles of 80.35 (15) and 78.37 (15)° with pyridinium and benzene rings of the cation, respectively.

Refinement
Hydroxy and water H atoms were located in difference maps and refined isotropically. The remaining 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.

Computing details
Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008), PLATON (Spek, 2009) and publCIF (Westrip, 2010).   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.59 e Å −3 Δρ min = −0.82 e Å −3 Extinction correction: SHELXTL (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.026 (3) 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.

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