(E)-2-[4-(Dimethylamino)styryl]-1-methylpyridinium triiodide

The asymmetric unit of the title compound, C16H19N2 +·I3 −, contains a (E)-2-[4-(dimethylamino)styryl)-1-methylpyridinium cation and half each of two triiodide anions. The complete triiodide anions are each generated by inversion symmetry. The planar cation has all of its eighteen non-H atoms situated on a mirror plane. In the crystal, the cations are stacked along the b axis by π–π interactions with a centroid–centroid distance of 3.5757 (13) Å. The triiodide anions are located between the cations. The crystal structure is further consolidated by short C⋯C [3.322 (9)–3.3952 (19) Å] contacts.

The asymmetric unit of the title compound, C 16 H 19 N 2 + ÁI 3 À , contains a (E)-2-[4-(dimethylamino)styryl)-1-methylpyridinium cation and half each of two triiodide anions. The complete triiodide anions are each generated by inversion symmetry. The planar cation has all of its eighteen non-H atoms situated on a mirror plane. In the crystal, the cations are stacked along the b axis byinteractions with a centroid-centroid distance of 3.5757 (13) Å . The triiodide anions are located between the cations. The crystal structure is further consolidated by short CÁ Á ÁC [3.322 (9)-3.3952 (19) Å ] contacts.

Comment
Pyridinium halide salts, generally possess surface active and interesting antimicrobial properties. They contain reactive functional groups covalently bound to the long hydrophobic chain and can exhibit biological activity (Fisicaro et al., 1990;Chanawanno et al., 2010). It has been proven that one of the factors which control their antimicrobial activity is the presence of anions in the compounds. In the work done by Pernak and coworkers, it was shown that the various anion types can exhibit different antimicrobial activities (Pernak et al., 2001). As our ongoing research is aimed at enhancing the antimicrobial activity of pyridinium salts, we have synthesized pyridinium salts with various anions in order to investigate the relationship between the types of anion and their antimicrobial properties. In the course of this work, the title compound (I) was synthesized and its crystal structure is reported here.  (Allen et al., 1987) and angles in (I) are in normal ranges and comparable to those found in related structures Zhang et al., 2008).

Experimental
The title compound was synthesized by mixing a solution of (E)-2-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (Zhang et al., 2008) (0.20 g, 0.55 mmol) in hot methanol (50 ml) and a solution of CuI 2 (0.17 g, 0.55 mmol) in hot methanol (30 ml). The mixture was stirred for half an hour and then left at room temperature. The title compound was formed as a red solid after 2 days. Orange needle-shaped single crystals suitable for x-ray structure determination were obtained by recrystallization from ethanol by slow evaporation of the solvent at ambient temperature over several days, M.p. >573 K.

Refinement
All H atoms were placed in calculated positions with d(C-H) = 0.95 Å, U iso =1.2U eq (C) for aromatic and CH and 0.96 Å, U iso = 1.2U eq (C) for CH 3 atoms. The highest residual electron density peak is located at 0.92 Å from I3 and the deepest hole is located at 0.66 Å from C16.
Figures Fig. 1. The asymmetric unit of (I) showing 50% probability displacement ellipsoids and the atom-numbering scheme. Atoms I2A and I4A were generated by symmetry codes 1 -x, y, -z and 1 -x, y, 1 -z, respectively whereas one of the three H atoms on each of the three methyl groups are generated by symmetry code x, -y, z.

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. 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.