(E)-4-[2-(4-Ethoxyphenyl)ethenyl]-1-methylpyridinium 4-bromobenzenesulfonate methanol hemisolvate

In the title compound, C16H18NO+·C6H4BrO3S−·0.5CH3OH, the cation exists in the E configuration and the whole molecule of the cation, except for the O atom of the ethoxy group, is disordered with a site-occupancy ratio of 0.695 (5):0.305 (5). The cation is disordered in such a way that the ethenyl units of the major and minor components are related by 180° around the long molecular axis. In the major component, the cation is almost planar, the dihedral angle between the pyridinium and benzene rings being 0.8 (3)°, whereas in the minor component, the dihedral angle between the two aromatic rings is 4.2 (6)°. In the crystal, the cations are stacked in an antiparallel manner along the a axis, while the anions and methanol molecules are linked through O—H⋯O hydrogen bonds and Br⋯O short contacts [3.0248 (13) Å] into a tape along the same direction. The three components are further linked by weak C—H⋯O, C—H⋯Br and C—H⋯π interactions.


Comment
Organic crystals with extensive conjugated π systems with large hyperpolarizability which exhibit NLO properties have been reported (Ogawa et al., 2008;Ruanwas et al., 2010;Yang et al., 2007). Styryl pyridinium derivatives are considered to be good conjugated π-systems Cheng, Tam, Stevenson et al., 1991). In our on-going research in searching for NLO materials (Chantrapromma et al., 2006;Chantrapromma, Jansrisewangwong et al., 2009;Ruanwas et al., 2010), the title compound (I) was synthesized. Unfortunately (I) crystallizes in the triclinic centrosymmetric space group P-1 and did not exhibit second-order nonlinear optical properties.
The asymmetric unit of (I) consists of one C 16 H 18 NO + cation, one C 6 H 4 BrO 3 Sanion and one-half of the CH 3 OH molecule. The whole molecule except the O atom of the ethoxy group (O1) of the cation is disordered over two sites with the major component A and the minor B components having refined site-occupancy ratio of 0.695 (5):0.305 (5) (Fig. 1). The cation exists in the E configuration with respect to the C6═C7 double bond and the torsion angle C5-C6-C7-C8 = -179.6 (2)°f or major component A and 179.5 (6)° for minor component B indicating that the orientation of the ethenyl moiety in major and minor components is related by 180° rotation. In the major component A, the cation is planar with the dihedral angle between the pyridinium and benzene rings being 0.8 (3)°, whereas in the minor component B, the dihedral angle between the two aromatic rings is 4.2 (6)°. The anion is inclined to the cation with the dihedral angle between the C17-C22 benzene ring of the anion and the mean plane of the conjugated π system (C1-C13/N1) [r.m.s = 0.013 (2) and 0.033 (2) Å for major and minor components, respectively] of the cation being 79.73 (12) and 79.2 (2)° for major and minor components, respectively.
In the crystal packing (Fig. 2), the cations and anions are individually arranged into chains along the a axis. The methanol molecules are linked to the anions by C-H···Br weak interactions and O-H···O hydrogen bonds, respectively (Table 1). The

cations, anions and methanol molecules are linked together by O-H···O hydrogen bonds and C-H···O weak interactions
forming sheets parallel to the bc plane. The crystal structure is further stabilized by C-H···π interactions (Table 1). A Br···O short contact [3.0248 (13) Å; symmetry code: 1 + x, y, z] was observed.
Experimental (E)-4-(4-Ethoxystyryl)-1-methylpyridinium iodide (compound A) was prepared by mixing 1:1:1 molar ratio solutions of 1,4-dimethylpyridinium iodide (2.00 g, 8.5 mmol), 4-ethoxybenzaldehyde (1.27 g, 8.5 mmol) and piperidine (0.84 ml, 8.5 mmol) in hot methanol (50 ml). The resulting solution was refluxed for 3 h under a nitrogen atmosphere. The resultant solid was filtered off and washed with diethylether to give oranged-yellow solid of compound A (2.18 g, 69%), M.p. 491-492 K. Silver (I) 4-bromobenzenesulfonate (compound B) was synthesized according to our previously reported procedure supplementary materials sup-2 (Chantrapromma et al., 2006). The title compound was synthesized by mixing a solution of compound A (0.20 g, 0.5 mmol) in hot methanol (25 ml) and a solution of compound B (0.17 g, 0.5 mmol) in hot methanol (50 ml). The mixture immediately yielded a grey precipitate of silver iodide. After stirring the mixture for 30 min, the precipitate of silver iodide was removed and the resulting solution was evaporated yielding a yellow solid of the title compound. Yellow plate-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, M.p. 513-515 K.

Refinement
All 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, 0.97 Å for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atoms 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 0.30 Å from H23B and the deepest hole is located at 0.68 Å from Br1. The whole cation, with the exception of the O1 atom of the ethoxy group, is disordered over two sites with a refined occupancy ratio of 0.695 (5):0.305 (5). All atoms of the minor component B were refined isotropically.
Initially rigidity and similarity restraints were applied. After steady state has been reached, these restraints were removed and DFIX restraints were applied to O1-C11A, O1-C11B, O1-C15A and O1-C15B bond distances. The occupancy of the metahnol molecule was refined to 0.542 (7). In the final refinement, it was fixed to 0.5. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme. Open bonds show the minor component.

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.

sup-4
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.