(E)-2-[4-(Diethylamino)styryl]-1-ethylpyridinium iodide monohydrate

In the title hydrated salt, C19H25N2 +·I−·H2O, the 4-(diethylamino)phenyl unit of the cation is disordered over two positions in a 0.847 (3):0.153 (3) ratio. The cation is twisted, with dihedral angles between the pyridinium and benzene rings of 11.25 (13) and 10.7 (8)° for the major and minor components, respectively. In the crystal, the three components are linked into a centrosymmetric 2:2:2 unit by O—H⋯I and C—H⋯O hydrogen bonds. π–π interactions with centroid–centroid distances of 3.5065 (7)–3.790 (9) Å are also present.


Hoong-Kun Fun Comment
Aminostyryl pyridinium (ASP) salts have been widely synthesized and used as fluorescence dyes for lymphocytes labeling and preliminary diagnostic imaging studies on dogs having a sodium-urate-induced inflammation in their stifle joints (Larnbert et al., 1996). Moreover, ASP salts have been reported to possess antibacterial activity (Chanawanno et al., 2010). During the course of our research on synthesis and antibacterial activity of quaternary ammonium compounds (Chanawanno et al., 2010;Kaewmanee et al., 2010), the title aminostyryl pyridinium derivative (I) was synthesized and tested for antibacterial activity. Our antibacterial assay showed that (I) exhibit moderate activity against Pseudomonas aeruginosa. Herein its crystal structure is reported.

Experimental
The title compound (I) was prepared by mixing 1:1:1 molar ratio solutions of 1-ethyl-2-methylpyridinium iodide (1 g, 4 mmol), 4-diethylaminobenzaldehyde (0.7 g, 4 mmol) and piperidine (0.4 ml, 4 mmol) in methanol (40 ml). The resulting solution was stirred for 4 h under a nitrogen atmosphere. The orange solid which formed was filtered and washed with diethylether. Orange block-shaped single crystals of (I) suitable for x-ray structure determination were recrystallized from methanol by slow evaporation at room temperature over a few weeks, M.p. 446-448 K.

Refinement
Water H atoms were located in a difference Fourier map and the positions were refined freely, with U iso (H) = 1.5U eq (O).
The remaining H atoms were fixed geometrically and all hydrogen atoms were allowed to ride on their parent atoms, with d(C-H) = 0.95 for aromatic and CH, 0.99 for CH 2 and 0.98 Å for CH 3 atoms. Their U iso values were constrained to be 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the remaining H atoms. A rotating group model was used for the methyl groups. The 4-diethylaminophenyl unit is disordered over two sites with refined site occupancies of 0.847 (3)      The crystal packing of the major component viewed along the b axis. Hydrogen bonds are drawn as dashed lines. Special details Experimental. The data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (