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

In the title compound, C18H23N2 +·I−, the cation exists in the E configuration with respect to the ethenyl C=C bond. The pyridinium and benzene rings are nearly coplanar, making a dihedral angle of 4.63 (7)°. The two ethyl groups of the diethylamino substituent point in opposite directions with respect to the benzene plane. In the crystal, the cation and the iodide anion are linked by a weak C—H⋯I interaction. The cations are stacked in an anti-parallel manner along the a axis by a π–π interaction with a centroid–centroid distance of 3.5262 (9) Å. The crystal structure is further stabilized by C—H⋯π interactions.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 Comment For a long time, styryl pyridinium quaternary ammonium compounds were known to exhibit antiseptic properties (Browning et al., 1922(Browning et al., , 1923. However medicinal researchers have long neglected to further develop the styryl pyridinium chromophore compounds for use as antibacterial agents due to the superior properties of penicillin until the incoming of the penicillin-resistant bacteria phenomenon, for example, methicillin-resistant Staphylococcus aureus, MRSA. The most interesting feature of styryl pyridinium quaternary ammonium compounds is their very specific activity to MRSA which is a vital drug-resistant bacteria (Wainwright & Kristiansen, 2003;Chanawanno et al., 2010). From this significant reason, our research group has synthesized and characterized several styryl pyridinium derivatives including the title compound (I) in order to search for new potent antibacterial agents. Herein we report the crystal structure of (I).  (Allen et al., 1987) and comparable to those in related structures (Chanawanno et al., 2008;Fun et al., 2009).
In the crystal packing ( Fig. 2), the cations are arranged in a zig-zag manner along the b axis with the iodide ions located in the interstitials of the cations and linked to the cations by a C-H···I weak interaction (Table 1). The cations stacked approximately along the a axis in an antiparallel manner by π-π interaction with the Cg1···Cg2 iii distance of 3.5262 (9) Å [symmetry code: (iii) 1-x, 1-y, 1-z]; Cg1 and Cg2 are centroids of N1/C1-C5 and C8-C13 rings, respectively. The crystal structure is further stabilized by C-H···π interactions (Table 1).

Experimental
The title compound (I) was prepared by mixing 1:1:1 molar ratio solutions of 1,2-dimethylpyridinium iodide (2 g, 8.5 mmol), 4-diethylaminobenzaldehyde (1.52 ml, 8.5 mmol) and piperidine (0.84 ml, 8.5 mmol) in methanol (40 ml). The resulting solution was refluxed for 6 hours 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. 527-529 K).

Refinement
All H atoms were located in a difference map and refined isotropically. The highest residual electron density peak is located at 1.57 Å from I1 and the deepest hole is located at 0.48 Å from I1. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme.

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.
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.
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.