(E)-1-Methyl-4-styrylpyridinium iodide monohydrate

In the title compound, C14H14N+·I−·H2O, the cation is essentially planar, with a dihedral angle of 2.55 (7)° between the pyridinium and phenyl rings, and exists in an E configuration with respect to the ethenyl bond. In the crystal structure, the cations are stacked in an antiparallel manner along the a axis. The cation is linked to the water molecule by a weak C—H⋯O interaction, and the water molecule is further linked to the I− ion by O—H⋯I hydrogen bonds. The crystal structure is consolidated by these interactions and is further stabilized by a π–π interaction between the pyridinium and phenyl rings with a centroid–centroid distance of 3.6850 (8) Å.

In the title compound, C 14 H 14 N + ÁI À ÁH 2 O, the cation is essentially planar, with a dihedral angle of 2.55 (7) between the pyridinium and phenyl rings, and exists in an E configuration with respect to the ethenyl bond. In the crystal structure, the cations are stacked in an antiparallel manner along the a axis. The cation is linked to the water molecule by a weak C-HÁ Á ÁO interaction, and the water molecule is further linked to the I À ion by O-HÁ Á ÁI hydrogen bonds. The crystal structure is consolidated by these interactions and is further stabilized by ainteraction between the pyridinium and phenyl rings with a centroid-centroid distance of 3.6850 (8) Å .

Comment
The design and synthesis of nonlinear optical (NLO) materials have been receiving much attention due to their numerous applications (Chemla & Zyss, 1987;Prasad & Williams, 1991). In the search for new organic NLO materials, aromatic compounds with extended π-conjugation system are extensively studied (Chia et al., 1995;Dittrich et al., 2003). Such materials require molecular hyperpolarizability and orientation in a noncentrosymmetric arrangement of the bulk material (Lin et al., 2002;Prasad & Williams, 1991). During the course of our systematic studies of organic NLO materials, we have previously synthesized and reported the crystal structures of pyridinium and quinolinium iodide (Chanawanno et al., 2008;Chantrapromma, Jindawong, Fun & Patil, 2007). Herein we report the crystal structure of the title pyridinium derivative (I). However (I) crystallizes in centrosymmetric P2 1 /c space group which precludes the second-order nonlinear optical properties.
In the crystal packing (Fig. 2), the cations are stacked in an antiparallel manner along the a axis. The cation is linked with the water molecule by a C-H···O weak interaction. The water molecule is further linked with the Iion by O-H···I hydrogen bonds, forming a 3D network (Table 1). The crystal is consolidated by these interactions and further stabilized by π-π interactions with a distance of Cg 1 ···Cg 2 iii = 3.6850 (8)  supplementary materials sup-2

Refinement
Water H atoms were located in a difference map 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. The highest residual electron density peak is located at 0.70 Å from I1 and the deepest hole is located at 0.54 Å from I1. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.

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.