2-[(E)-2-(4-Chlorophenyl)ethenyl]-1-methylpyridinium iodide monohydrate1

In the title compound, C14H13ClN+·I−·H2O, the cation is nearly planar and exists in an E configuration; the dihedral angle between the pyridinium and benzene rings is 0.98 (17)°. The cations stack in an anti-parallel manner along the a axis through two π–π interactions between the pyridinium and benzene rings [centroid–centroid distances 3.569 (2) and 3.6818 (13) Å, respectively]. The cation, anion and water molecule are linked into a chain along the a axis by weak C—H⋯O and C—H⋯I interactions together with O—H⋯I hydrogen bonds and the chains are further connected into a three-dimensional network.

In the title compound, C 14 H 13 ClN + ÁI À ÁH 2 O, the cation is nearly planar and exists in an E configuration; the dihedral angle between the pyridinium and benzene rings is 0.98 (17) . The cations stack in an anti-parallel manner along the a axis through twointeractions between the pyridinium and benzene rings [centroid-centroid distances 3.569 (2) and 3.6818 (13) Å , respectively]. The cation, anion and water molecule are linked into a chain along the a axis by weak C-HÁ Á ÁO and C-HÁ Á ÁI interactions together with O-HÁ Á ÁI hydrogen bonds and the chains are further connected into a three-dimensional network.

Comment
In the last two decades, many efforts were focused on the discovery of new organic materials which exhibit large nonlinear optical (NLO) properties and would have applications in the fields of optoelectronics and photonics (Lakshmanaperumal et al., 2004;Marder et al., 1994;Qiu et al., 2007;Zhai et al., 1999;Zhan et al., 2006). In order to obtain second-order NLO single crystals, the main requirements should be the choice of molecules with large hyperpolarizability (β) and the alignment of these molecules with optimal orientation into a noncentrosymmetric space group in the crystal (Williams, 1984). Among the known organic NLO materials, ionic chromophores are of great interest because they exhibit large first hyperpolarizabilities (β) and have high melting points and hardness of their crystals. At the molecular level, a generally popular approach towards NLO materials is to design and synthesize compounds with extended conjugated π-systems with donor and acceptor groups because such compounds are likely to exhibit large values of molecular hyperpolarizability (β) and to possess polarization. Styryl pyridinium derivatives are considered to be good conjugated π-systems. In continuation of our on-going research on nonlinear optical materials (Chantrapromma et al., 2007a,b,c), the title compound, (I), was synthesized and the X-ray structure analysis was carried out in order to obtain detailed information about the molecular packing. However, compound (I) crystallizes in monoclinic space group P2 1 /c and doesn't exhibit second-order nonlinear optic properties.
The packing of the molecule down the c axis ( Fig. 2), showing that the cation is linked with water molecule by weak C-H···O interactions (Table 1) and linked with Ianions by weak C-H···I interactions (Table 1) whereas the Ianion is linked with water molecule by O-H···I hydrogen bonds, forming one-dimensional chains along the a axis. These chains are further connected into a three-dimensional network (Fig. 2). π···π interactions involving pyridinium and benzene rings were also observed with Cg 1 ···Cg 2 distances of 3.662 (2) Å (symmetry code; 1 -x, -y, 1 -z) and 3.569 (2) Å (symmetry code; 2 -x, -y, 1 -z); Cg 1 and Cg 2 are the centroids of the N1/C1-C5 pyridinium and C8-C13 benzene rings, respectively.
The crystal is stabilized by O-H···I hydrogen bond, weak C-H···O and C-H···I interactions.

Experimental
The title compound was prepared by mixing solutions of 1,2-dimethylpyridinium iodide, 4-chlorobenzaldehyde and piperidine (1:1:1 molar ratio) in methanol. The resulting solution was refluxed for 12 hr under a nitrogen atmosphere. The solid which formed was filtered and washed with chloroform. Orange plate-like single-crystal suitable for X-ray diffraction supplementary materials sup-2 analysis was obtained by recrystallization from methanol by slow evaporation of the solvent at ambient temperature after several days, Mp. 492-493 K.

Refinement
All H atoms were placed in calculated positions (O-H = 0.85-0.86 and C-H = 0.93-0.96 Å) and refined as riding, with U iso (H) = 1.2U eq (C) or 1.5U eq (O, methyl C), A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.76 Å from I1 and the deepest hole is located at 0.59 Å from I1.

Special details
Experimental. The data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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 Rfactors(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.