The iodide salt of 3-cyano-N-methylpyridinium cation crystallizes as yellow needles in the monoclinic space group P21/n with a = 4.8726(5), b = 12.9380(15), c = 13.4629(15) Å, β = 97.463(2)○, and Z = 4 (mp 196○C). The chloride salt forms colorless plates in the monoclinic space group P21/m with a = 7.9488(8), b = 6.4023(7), c = 8.0844(8) Å, β = 112.987(2)○, and Z = 2 (mp > 220○C). For ring hydrogens interacting with the anion, each salt has C–H ⋅ ⋅ ⋅ X distances and angles consistent with weak hydrogen bonds as described by recently published criteria (Brammer et al.Cryst. Growth Design 2001, 1, 277; Steiner Acta Crystallogr., Sect B 1998, 54, 456; Crystallogr. Rev. 1996, 6, 1). The chloride salt has an additional interaction between H5 and the cyano nitrogen on an adjacent cation in the same layer, or a total of four coplanar hydrogen bonds per cation. It forms sheets which stack along the b axis. The iodide has fewer hydrogen bonds from the ring and the cations are tilted relative to each other. There is an unusual hydrogen bond from a methyl hydrogen to a cyano nitrogen in the iodide. Roughly oval (3.8 × 5.7 Å) open channels bounded by H5 and iodides run along the a axis. Stabilization of these solids by hydrogen bonding is estimated to be at least 1.9 kcal/mole more for the chloride than for the iodide.
Weak hydrogen bond 3-cyano-N-methylpyridinium chloride iodide