4-Cyano-1-methylpyridinium iodide

In the crystal structure of the title compound, C7H7N2 +·I−, the cations form inversion-related dimers via weak pairwise C—H⋯N hydrogen bonds. In the dimers, the pyridinium rings are parallel to one another with their mean planes separated by a normal distance of ca 0.28 Å. Weak C—H⋯N interactions between adjacent dimers generate a layer lying parallel to (10-1). The remaining H atoms form C—H⋯I interactions, which link the layers into a three-dimensional structure.

In the crystal structure of the title compound, C 7 H 7 N 2 + ÁI À , the cations form inversion-related dimers via weak pairwise C-HÁ Á ÁN hydrogen bonds. In the dimers, the pyridinium rings are parallel to one another with their mean planes separated by a normal distance of ca 0.28 Å . Weak C-HÁ Á ÁN interactions between adjacent dimers generate a layer lying parallel to (101). The remaining H atoms form C-HÁ Á ÁI interactions, which link the layers into a three-dimensional structure.

Comment
Previously reported structures of four other cyano-1-methylpyridinium salts (Koplitz et al., 2003;Mague et al., 2005;Koplitz et al., 2012) include three layered compounds with all atoms, except the methyl H atoms, lying on crystallographic mirror planes. Interestingly, none of the iodide salts of the 4-, 3-and 2-cyano-1-methylpyridinium cation adopt this layer structure, possibly because the larger size and weaker hydrogen-bonding ability of iodide as compared with the smaller chloride and bromide ions provides a less restrictive set of interionic interactions.
The molecular structure of the title compound is illustrated in Fig. 1. In the crystal, the cations form inversion dimers via weak pairwise C2-H2···N2 hydrogen bonds (Table 1). In the dimers the pyridinium rings are parallel to one another with their mean planes separated by a normal distance of ca 0.28 Å. Weak C1-H1B···N2 interactions between adjacent dimers generate a layer lying parallel to (101), with the remaining hydrogen atoms forming C-H···I interactions ( Table   1). The latter reinforce the construction of the layers as well as tying them together into a three-dimensional structure ( Fig. 2).
In contrast to 3-cyano-1-methylpyridinium iodide (Koplitz et al., 2003) where each iodide ion interacts with three C-H groups, in the title compound each anion is linked by five C-H groups which may reflect the more linear shape of the cation in the present structure.
Experimental 4-Cyanopyridine (10.55 g) was dissolved in benzene (40 ml). Iodomethane (9.5 ml) was added to this solution slowly with stirring and the solution was refluxed for 75 minutes. A yellow solid was collected by vacuum filtration (M.p. 462 -466 K). Addition of ethanol to the supernatant (ca 2:1 benzene:ethanol) resulted in the the growth overnight of thin platelike yellow crystals of the title compound, suitable for X-ray diffraction.

Refinement
The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.95 and 0.98 Å for CH and CH 3 H-atoms, respectively, with U iso (H) = k × U eq (C), where k = 1.5 for CH 3 H-atoms and 1.2 for other H-atoms.