2-[(E)-2-(4-Ethoxyphenyl)ethenyl]-1-methylquinolinium iodide dihydrate

In the title compound, C20H20NO+·I−·2H2O, the cation is almost planar (r.m.s. deviation = 0.038 Å) and exists in an E configuration. The dihedral angle between the quinolinium ring system and the benzene ring is 0.7 (4)°. In the crystal structure, the cations are stacked in an anti-parallel manner along [100] with π–π interactions between the pyridinium and ethoxybenzene rings [centroid–centroid distance = 3.678 (5) Å]. The cations, iodide anions and water molecules are linked together through O—H⋯O, O—H⋯I and C—H⋯I hydrogen bonds into a two-dimensional network parallel to (001).

In the title compound, C 20 H 20 NO + ÁI À Á2H 2 O, the cation is almost planar (r.m.s. deviation = 0.038 Å ) and exists in an E configuration. The dihedral angle between the quinolinium ring system and the benzene ring is 0.7 (4) . In the crystal structure, the cations are stacked in an anti-parallel manner along [100] withinteractions between the pyridinium and ethoxybenzene rings [centroid-centroid distance = 3.678 (5) Å ]. The cations, iodide anions and water molecules are linked together through O-HÁ Á ÁO, O-HÁ Á ÁI and C-HÁ Á ÁI hydrogen bonds into a two-dimensional network parallel to (001).

Comment
Organic crystals are highly recognized as materials of the future because their molecular nature combined with versatility of synthetic chemistry can be used to alter their structures in order to maximize the nonlinear optical (NLO) properties (Kagawa et al., 1994). The title quinolinium salt, (I), was synthesized in order to study its NLO properties. In addition, quinolinium derivatives were found to exhibit interesting bioactivities and pharmacological activities (Hopkins et al., 2005;Kaminsky & Meltzer, 1968;Musiol et al., 2006;O'Donnell et al., 2010). Due to the well-known bioactivities of quinoline core, the antibacterial activities of (I) were also evaluated. Our results show that (I) is very active against the Methicillin-Resistant Staphylococcus aureus with a very low MIC value of 2.34 µg/ml, whereas it is inactive against the Gram-negative bacteria i.e. Pseudomonas aeruginosa, Salmonella typhi and Shigella sonnei. Nevertheless (I) did not possess NLO properties since it crystallized in the centrosymmetric triclinic P-1 space group (Williams, 1984).
In the crystal, the cations are arranged into layers parallel to the (100) and stacked in anti-parallel manner along the a axis with π-π interactions involving the quinolinium ring system and benzene ring [Cg1···Cg2 ii = 3.678 (5) Å; symmetry code as in Table 1; Cg1 and Cg2 are centroids of the N1/C1/C6-C9 and C12-C17 rings, respectively]. The Iions and water molecules are located in the interstitial sites of the cations. The cations, Ianions and water molecules are linked together through O-H···O, O-H···I and C-H···I hydrogen bonds (Table 1) into a two-dimensional network parallel to the (001) (Fig. 2).

Experimental
The title compound was prepared by mixing a solution (1:1:1 mole ratio) of 1,2-dimethylquinolinium iodide (2.00 g, 7.0 mmol), 4-ethoxybenzaldehyde (4.32 ml, 7.0 mmol) and piperidine (0.69 ml, 7.0 mmol) in hot methanol (50 ml). The resulting solution was refluxed for 6 h under nitrogen atmosphere. The resultant orange-brown solid was filtered, washed with diethyl ether, dried in vacuo and purified by recrystallization. Brown needle-shaped single crystals of the title compound suitable for X-ray structure determination were obtained from methanol solution by slow evaporation at room temperature after several days (m.p. 492-494 K).

Refinement
The water H atoms were initially located in a difference map and were refined with O-H and H···H distance restraints of 0.84 (1) and 1.37 (2) Å, respectively. During the final stages of the refinement they were allowed to ride on their parent O atoms with U iso (H) = 1.5U eq (O). The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 Å (aromatic) and 0.96 Å (CH 3 ). 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. The U ij components of atoms C1, C6 and C9 were restrained to approximate isotropic behaviour. A rigid bond restraint with an s.u. of 0.01 was applied to the atomic displacement parameters of atoms C2 and C3 (also C12 and C17), because the components of the displacement parameters in the direction of the bond between these atoms were slightly inconsistent. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 1.17 Å from I1 and the deepest hole is located at 1.46 Å from C11. Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level.  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.

2-[(E)-2-(4-Ethoxyphenyl)ethenyl]-1-methylquinolinium iodide dihydrate
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.