(E)-1-Methyl-2-styrylpyridinium iodide

In the title compound, C14H14N+·I−, the cation exists in an E configuration with respect to the ethenyl bond and is slightly twisted, the interplanar angle between the pyridinium and phenyl rings of the cation being 4.8 (2)°. In the crystal packing, the cations are stacked in an antiparallel fashion along the a axis by a π–π interaction involving both pyridinium and phenyl rings; the centroid–centroid distance is 3.542 (3) Å. Each iodide ion is sandwiched between two cations. The cations and iodide anions are linked together by weak C—H⋯I interactions, giving rise to ladder-like ribbons along the a axis.


Comment
In the search for new materials capable of nonlinear optical (NLO) applications, many studies have focused on organic molecules containing highly polarizable π-conjugated backbones (Wenseleers et al., 1998). During the course of our screening for NLO active organic compounds, we have previously reported the crystal structures of pyridinium derivatives (Chanawanno et al., 2008;Chantrapromma et al., 2009a,b); Fun et al., 2009). In this paper we report the synthesis of the title compound whose crystal structure was undertaken in order to establish the conformation and crystal packing. The title compound crystallized in centrosymmetric space group P2 1 /c so it does not exhibit second-order nonlinear optical properties.
In the crystal packing ( Fig. 2), the cations are stacked in an antiparallel fashion along the a axis by a π-π interaction with the Cg1···Cg2 distance = 3.542 (3) Å (symmetry code: 2-x, 1-y, 1-z); Cg1 and Cg2 are the centroids of the N1/C1-C5 and C8-C13 rings, respectively. Each iodide ion is sandwiched between two cations. The cations and iodide anions are linked together by weak C-H···I interactions, giving rise to ladder-like ribbons along the a axis (Table 1 and Fig. 2). The crystal structure is stabilized by C-H···I and π-π interactions.

Experimental
The title compound was prepared by mixing 1:1:1 molar ratio solutions of 1,2-dimethylpyridinium iodide (2 g, 8.5 mmol), benzaldehyde (0.86 ml, 8.5 mmol) and piperidine (0.84 ml, 8.5 mmol) in methanol (40 ml). The resulting solution was refluxed for 5 hours under a nitrogen atmosphere. A pale yellow solid of the resulting compound was formed, this was then filtered and washed with diethyl ether. Yellow needle-shaped single crystals of the title compound suitable for x-ray structure determination were recrystallized from methanol by slow evaporation at room temperature after several weeks, Mp. 505-506 K. Details of the stability of the temperature controller used in the data collection have been published earlier (Cosier & Glazer, 1986).

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic C 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 0.75 Å from I1 and the deepest hole is located at 0.67 Å from I1. Fig. 1. The molecular structure of the title compound, with 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen atoms are drawn as spheres of arbitrary radius.

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.