1-Methyl-2-[(E)-2,4,5-trimethoxystyryl]pyridinium iodide

In the title compound, C17H20NO3 +·I−, the cation exists in the E configuration. The pyridinium and benzene rings are close to coplanar, with a dihedral angle of 7.43 (12)° between them. The three methoxy groups of 2,4,5-trimethoxyphenyl are essentially coplanar with the benzene plane, with C—O—C—C torsion angles of 1.0 (3), −1.9 (3) and 3.6 (3)°. A weak intramolecular C—H⋯O interaction generates an S(6) ring motif. In the crystal, the cations are stacked in columns in an antiparallel manner along the a axis through π–π interactions, with a centroid–centroid distance of 3.7714 (16) Å. The iodide anion is situated between the columns and linked to the cation by a weak C—H⋯I interaction.

In the title compound, C 17 H 20 NO 3 + ÁI À , the cation exists in the E configuration. The pyridinium and benzene rings are close to coplanar, with a dihedral angle of 7.43 (12) between them. The three methoxy groups of 2,4,5-trimethoxyphenyl are essentially coplanar with the benzene plane, with C-O-C-C torsion angles of 1.0 (3), À1.9 (3) and 3.6 (3) . A weak intramolecular C-HÁ Á ÁO interaction generates an S(6) ring motif. In the crystal, the cations are stacked in columns in an antiparallel manner along the a axis throughinteractions, with a centroid-centroid distance of 3.7714 (16) Å . The iodide anion is situated between the columns and linked to the cation by a weak C-HÁ Á ÁI interaction.

Comment
We have previously synthesized several pyridinium and quinolinium derivatives to study their antibacterial activities and non-linear optical (NLO) properties (Chanawanno et al., 2008Chantrapromma et al., 2010;Fun et al., 2009;Ruanwas et al., 2010). During the course of antibacterial activities and NLO properties of synthetic compounds, the title pyridinium derivative was synthesized and its single crystal x-ray structural study was undertaken in order to establish the conformation of the various groups and the space group. The title compound (I) crystallized in the centrosymmetric triclinic P-1 space group and therefore (I) does not exhibit second order NLO properties (Williams, 1984). In addition (I) was also tested for antibacterial activities against the Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Methicillin-Resistant Staphylococcus aureus, Vancomycin-Resistant Enterococcus faecalis, Pseudomonas aeruginosa, Salmonella typhi and Shigella sonnei, and found inactive. Herein the crystal structure of (I) is reported. An intramolecular C6-H6A···O1 weak interactions generates an S(6) ring motif (Bernstein et al., 1995) which helps to stabilize the planarity of the molecular structure. The methyl units of two methoxy groups at atoms C9 and C11 point towards whereas at atoms C11 and C12 point away from each other ( Fig. 1). It is interesting to note that there is steric interaction between the methyl group of 1-methylpyridinium and the methoxy group at atom C9 but the intramolecular C6-H6A···O1 weak interaction which formed the S(6) ring motif is more preferable than the S(5) ring motif comparing to the structure which the 2,4,5-trimethoxyphenyl unit rotate 180° around the C7-C8 bond to form S(5) ring motif of C7-H7A···O1 weak interaction. The bond lengths of cation in (I) are in normal ranges (Allen et al., 1987) and comparable to those in related structures (Chanawanno et al., 2008;Fun et al., 2009;Kaewmanee et al., 2010).
In the crystal packing (Fig. 2), the cations are stacked in an anti-parallel manner along the a axis by π-π interactions with the Cg1···Cg2 ii distance of 3.7714 (16) Å [symmetry code: (ii) 1 -x, -y, 1 -z]; Cg1 and Cg2 are the centroids of N1/C1-C5 and C8-C13 rings, respectively. The iodide anions are located in the interstitials of the cations and linked to the cations by C-H···I weak interactions (Table 1).
The resulting solution was refluxed for 5 hr under a nitrogen atmosphere. The resultant solid which formed was filtered off supplementary materials sup-2 and washed with diethyl ether. 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. 544-545 K).

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH and 0.96 Å for CH 3 atoms. 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. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 1.46 Å from I1 and the deepest hole is located at 1.00 Å from C6. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen bond was drawn as dashed line.

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.