(E)-2-[4-(Dimethylamino)styryl]-1-methylquinolinium iodide sesquihydrate

In the title compound, C20H21N2 +.I−·1.5H2O, the cation exists in the E configuration and is not planar. The dihedral angle between the quinolinium and dimethylaminophenyl rings is 9.26 (6)°. The O atom of one of the solvent water molecules lies on a twofold rotation axis. In the crystal structure, the cations form one-dimensional zigzag chains along the [001] direction. The cations are linked to water molecules and iodide ions through weak C—H⋯O and C—H⋯I interactions, respectively. Water molecules and iodide ions form O—H⋯O and O—H⋯I hydrogen bonds, which stabilize the crystal structure. A C—H⋯π interaction is also present.

In the title compound, C 20 H 21 N 2 +. I À Á1.5H 2 O, the cation exists in the E configuration and is not planar. The dihedral angle between the quinolinium and dimethylaminophenyl rings is 9.26 (6) . The O atom of one of the solvent water molecules lies on a twofold rotation axis. In the crystal structure, the cations form one-dimensional zigzag chains along the [001] direction. The cations are linked to water molecules and iodide ions through weak C-HÁ Á ÁO and C-HÁ Á ÁI interactions, respectively. Water molecules and iodide ions form O-HÁ Á ÁO and O-HÁ Á ÁI hydrogen bonds, which stabilize the crystal structure. A C-HÁ Á Á interaction is also present.

Comment
Organic molecules with large π systems have been extensively used in attempts to obtain non-linear optical (NLO) materials (Chia et al., 1995;Dittrich et al., 2003;Marder et al., 1994;Nogi et al., 2000;Otero et al., 2002;Pan et al., 1996;Sato et al., 1999). We have previously synthesized and crystallized several ionic organic salts of quinolinium derivatives which have a conjugate π system to study their non-linear optical properties (Chantrapromma et al., 2006;2007a;2007b;2007c;2007d;Jindawong et al., 2005). Previous investigations by Marder et al., 1994, Pan et al., 1996 andUmezawa et al.,  The asymmetric unit of the title compound consists of one C 20 H 21 N 2 + cation, one Ianion and 1.5 H 2 O molecules. The remaining cell contents are generated by symmetry with the O2W atom (symmetry code: -x, y, 1/2 -z) lying on a two-fold rotation axis. The cation exists in the E configuration with respect to the C10═C11 double bond [1.357 (2) Å] and is not planar as indicated by a dihedral angle of 9.26 (6)° between the quinolinium and the dimethylaminophenyl rings. This value is relatively wider than the corresponding angle (3.41 (7)°) reported for the closely related structure of the 4-methoxybenzenesulfonate salt of the same cation (Kobkeatthawin et al., 2008). This may be due to packing effects involving the different counterions. The orientation of the ethenyl unit with respect to the quinolinium and the dimethylaminophenyl rings can be indicated by the torsion angles C8-C9-C10-C11 = 8.5 (2)° and C10-C11-C12-C17 = -1.2 (2)°. The bond lengths and angles are in normal ranges (Allen et al., 1987) and are comparable to those in closely related structures (Chantrapromma et al., 2006;2007a;2007b;2007c;Kobkeatthawin et al., 2008).
The resulting solution was refluxed for 6 h under a nitrogen atmosphere. The resulting solid was filtered off, washed with methanol and recrystallized from methanol to give green crystals. Single crystals of the title compound suitable for x-ray structure determination were recrystalized from methanol/ethanol solvent (1:1 v/v) by slow evaporation of the solvent at room temperature after a few weeks. (Mp. 491-493 K).

Refinement
Water hydrogen atoms were located in a difference map and refined isotropically. H atoms attached to C were placed in calculated positions with d(C-H) = 0.93 Å, U iso =1.2U eq (C) for aromatic and CH, 0.96 Å, U iso = 1.5U eq (C) for CH 3 atoms.
A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.57 Å from I1 and the deepest hole is located at 0.46 Å from I1.