Bis[(E)-1-methyl-4-styrylpyridinium] 4-bromobenzenesulfonate iodide

In the title compound, 2C14H14N+·C6H4BrO3S−·I−, two crystallographically independent cations exist in an E configuration with respect to the C=C ethenyl bond. One cation is approximately planar, whereas the other is twisted slightly, the dihedral angles between the pyridinium and phenyl rings of each cation being 0.96 (15) and 7.05 (16)°. In the crystal structure, the cations are stacked in an antiparallel manner along the a axis through weak C—H⋯π interactions and π–π interactions, with centroid–centroid distances of 3.5544 (19) and 3.699 (2) Å. The 4-bromobenzenesulfonate anions and the cations are linked together by weak C—H⋯O interactions. A short Br⋯I contact [3.6373 (4) Å] and C—H⋯I interactions are also observed.


Comment
Organic molecules are promising candidates for the nonlinear optical (NLO) applications. Stilbene derivatives, especially the pyridinium stilbenes with Donor-π-Acceptor system, were recognized as a good organic NLO chromophore (Chia et al., 1995;Pan et al., 1996). We previously reported the systhesis and crystal structure of bis[(E)-1-methyl-4-styrylpyridinium] 4-chlorobenzenesulfonate iodide (I), a pyridinium stilbene derivative, which crystallizes in noncentrosymmetric P2 1 space group and exhibits second-order NLO properties (Fun et al., 2009;Prasad & Williams, 1991). In this work, the title compound (II) was synthesized by changing the 4-chlorobenzenesulfonate anionic part in (I) to the 4-bromobenzenesulfonate to study the different NLO properties. By changing this, it was found that the title compound (II) crystallizes in centrosymmetric P2 1 /c space group and does not show second-order NLO properties.
The title molecule consists of two C 14 H 14 N + (A and B), one C 6 H 4 BrO 3 Sand one Iions ( Fig. 1 (Allen et al., 1987) and comparable with the closely related compounds (Fun et al., 2009a,b;Fun et al., 2009).
In the crystal packing ( Fig. 2), all O atoms of the sulfonate group are involved in weak C-H···O interactions ( Table 1).

Experimental
(E)-1-methyl-4-styrylpyridinium iodide (compound A, 0.19 g, 0.58 mmol) which was prepared according the previous method (Fun et al., 2009) was mixed with silver (I) 4-bromobenzenesulfonate (0.20 g, 0.58 mmol) (Chantrapromma et al., 2006) in methanol solution and stirred for 30 minutes. The precipitate of silver iodide which formed was filtered and the filtrate was evaporated to give the title compound as an orange solid. Orange needle-shaped single crystals of the title com-supplementary materials sup-2 pound suitable for x-ray structure determination were recrystallized from methanol by slow evaporation at room temperature over a week (m.p. 472-473 K).

Refinement
All 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 (H) 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 0.78 Å from I1 and the deepest hole is located at 0.70 Å from I1. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.   Glazer, 1986) operating at 100.0 (1) K.

Figures
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.