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

In the title compound, 2C14H14N+·C6H4ClO3S−·I−, each cation exists in an E configuration with respect to the ethenyl bond. The dihedral angle between the pyridinium and benzene rings is 3.98 (6)° in one of the cations and 9.88 (7)° in the other. The two cations are arranged in an antiparallel manner with π–π interactions between pyridinium and benzene rings [centroid–centroid distance = 3.5805 (8) Å]. The benzene ring of the anion makes dihedral angles of 61.20 (6) and 64.25 (6)° with the pyridinium rings of the two cations. In the crystal, the cations are stacked in an antiparallel manner along the a axis, while the anions are linked into chains along the same direction. The ions are linked into a three-dimensional network by C—H⋯I and C—H⋯O hydrogen bonds and C—H⋯π interactions. The crystal under investigation was an inversion twin, with a ratio of 61.7 (5):38.3 (5) for the two components.


S1. Comment
There is a considerable interest in the synthesis of new materials with large second-order optical nonlinearities. Such materials require molecular first hyperpolarizability and orientation in a noncentrosymmetric arrangement (Lin et al., 2002;Prasad et al. 1991). During the course of our systematic studies of organic NLO materials, we have previously synthesized and reported crystal structures of a number of pyridinium derivatives (Chanawanno et al., 2008;Chantrapromma et al., 2007Chantrapromma et al., , 2009Fun et al., 2009a,b). Herein we report the crystal structure of the title pyridinium derivative which crystallizes in noncentrosymmetric P2 1 space group and exhibits second-order nonlinear optical properties.
The title molecule consists of two C 14 H 14 N + (A and B) cations, one C 6 H 4 ClO 3 Sanion and one Iion (Fig. 1); the two cations exist in an E configuration with respect to the C7═C8 ethenyl bond, with a C6-C7-C8-C9 torsion angle of 179.94 (12)° in A and 178.99 (12)° in B. One cation [A] is almost planar while the other [B] is slightly twisted; the dihedral angle between the pyridinium and benzene rings is 3.98 (6)° in the cation A and 9.88 (7)° in B. The orientation of the anion with respect to cations A and B is indicated by dihedral angles between the benzene ring of the anion and the pyridinium rings of the cations A and B of 61.20 (6) and 64.25 (6)°, respectively. Bond distances in both cations and anion have normal values (Allen et al., 1987) and are comparable with those observed in related structures (Fun et al., 2009a,b).
In the crystal packing ( Fig. 2), all O atoms of the sulfonate group are involved in weak C-H···O interactions ( Table 1).
The cations are stacked in an antiparallel manner along the a axis while the anions are linked into chains along the same direction. The cations are linked to the interstitial Iions by C-H···I weak interactions and are linked to anionic chains through C-H···O weak interactions (Table 1) forming a three-dimensional network. The crystal structure is further stabilized by C-H···π (Table 1) interactions, and π-π interactions with a Cg1···Cg3 distance of 3.5805 (8) Å (Cg1 and Cg3 are centroids of the C1A-C6A and C9B-C13B/N1B rings respectively. In addition, the crystal structure also shows short C···O [2.9706 (16) Å] and Cl···I [3.5917 (3) Å] contacts.
The mixture solution was stirred for 30 min, the precipitate of silver iodide which formed was filtered and the filtrate was evaporated to give the title compound as a yellow solid. Yellow needle-shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from a methanol solution by slow evaporation at room supporting information temperature over a few weeks (m.p. 468-469 K).

S3. 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 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 0.69 Å from I1 and the deepest hole is located at 1.14 Å from I1. The crystal under investigation was an inversion twin, with a ratio of 61.7 (5):38.3 (5) for the two components.

Figure 1
The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.  The crystal packing of the title compound viewed down the b axis. C-H···O and C-H···I interactions are shown as dashed lines. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.12 e Å −3 Δρ min = −0.44 e Å −3 Absolute structure: Flack (1983), 6221 Friedel pairs Absolute structure parameter: 0.383 (5) 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.