2-[(E)-2-(4-Hydroxy-3-methoxyphenyl)ethenyl]-1-methylpyridinium 4-bromobenzenesulfonate monohydrate

The title salt crystallized as the monohydrate C15H16NO2 +·C6H4BrSO3 −·H2O. The cation exists in an E conformation with respect to the ethynyl bond and is essentially planar, with a dihedral angle of 6.52 (14)° between the pyridinium and the benzene rings. The hydroxy and methoxy substituents are coplanar with the benzene ring to which they are attached, with an r.m.s. deviation of 0.0116 (3) Å for the nine non-H atoms [Cmethyl—O—C—C torsion angle = −0.8 (4)°]. In the crystal, the cations and anions are stacked by π–π interactions, with centroid–centroid distances of 3.7818 (19) and 3.9004 (17) Å. The cations, anions and water molecules are linked by O—H⋯O hydrogen bonds and weak C—H⋯O interactions, forming a three-dimensional network.


Comment
Stilbene-based compounds have been reported to possess a wide range of biological activities including antibacterial (Chanawanno et al., 2010) and antioxidant (Frombaum et al., 2012) activities and also non-linear optical (Ruanwas et al., 2010) and fluorescent properties (Li et al., 2013). We have previously reported several crystal structures and applications of stilbene derivatives (Chanawanno et al., 2009;2010, Kobkeatthawin et al., 2009, Ruanwas et al., 2010. Due to these interesting properties, the title pyridinium-stilbene salt, (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 an H 2 O molecule (Fig. 1). The cation exists in an E configuration with respect to the C6 ═C7 double bond [1.318 (4) Å] and the C5-C6-C7-C8 torsion angle is -178.0 (3)°. The cation is essentially planar with a dihedral angle between the pyridinium and benzene rings of the cation being 6.52 (14)°. The hydroxy and methoxy substituents lie close to the plane of the C8-C13 benzene ring with the r.m.s. deviation of 0.0116 (3) Å for the nine non-H atoms and with the torsion angle C15-O1-C10-C9 = -0.8 (4)°. All bond lengths (Allen et al., 1987) in both the cation and anion are normal and compare well with those found in closely related structures (Chanawanno et al., 2009;Chantrapromma et al., 2013;Fun et al., 2011).

1-Methyl-2-[(E)-2-(3-methoxy-4-hydroxyphenyl)ethenyl]pyridinium iodide (compound A) was prepared by mixing a
solution (1:1:1 molar ratio) of 1,2-dimethylpyridinium iodide (3.02 g, 12.84 mmol), vanillin (4-hydroxy-3-methoxybenzaldehyde, 1.95 g, 12.82 mmol) and piperidine (1.09 g, 12.80 mmol). The resulting solution was refluxed for 3 h under a nitrogen atmosphere. The solid which formed was filtered, washed with diethylether and recrystallized from methanol, to give brown crystals of compound A (2.69 g, 57% yield Mp. 526-527 K). Thereafter, the title compound was synthesized by mixing a solution of compound A (0.21 g, 0.58 mmol) in hot methanol (60 ml) and a solution of silver (I) 4-bromobenzenesulfonate (Jindawong et al., 2005), (0.20 g, 0.58 mmol) in hot methanol (40 ml). Upon mixing, a yellow precipitate of silver iodide was immediately formed which was removed by filtration and the orange filtrate was evaporated under reduced pressure to yield the title compound as an orange solid (0.27 g, 91% yield). Orange block- shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from methanol by slow evaporation of the solvent at room temperature over several days, Mp. 490-491 K.

Refinement
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(O-H) = 0.82 Å, 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.

Figure 1
The molecular structure of the title compound, showing 30% probability displacement ellipsoids.   π-π interactions between aromatic rings of the cations and anions.  (Cosier & Glazer, 1986) operating at 100.0 (1) K. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.