Lynn V. Koplitz

2-Cyano-1-methyl-pyridinium iodide.

The cation in the title compound, C7H7N2 +·I−, is planar (r.m.s. deviation for the nine fitted non-H atoms = 0.040 Å). The crystal packing is best described as undulating layers of cations and anions associated via C—H⋯I interactions.

2-Cyano-1-methylpyridinium nitrate

In the title compound, C7H7N2 +·NO3 −, all atoms except the methyl H atoms lie on a crystallographic mirror plane. The interlayer distance, including that between aligned N atoms from alternating cations and anions in adjacent layers, is exceptionally short at 3.055 (1) Å. Two-dimensional C—H⋯O hydrogen-bonded networks link cations to anions, while C—H⋯N interactions link cations within each layer. Anion–π interactions with the cations assist in binding the layers together.

The influence of weak hydrogen bonds on the properties of 3-cyano-N-methylpyridinium chloride and iodide

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.

3-Cyano-N-methyl­pyridinium bromide

The title compound, C7H7N2+·Br−, forms a layered solid with each cation forming three strong and one weaker C—H⋯Br hydrogen bonds within the layer. All atoms except two of the methyl H atoms lie on a mirror plane.

4-Cyano-1-methyl-pyridinium bromide.

In the crystal of the title molecular salt, C7H7N2 +·Br−, the cations form inversion dimers via weak pairwise C—H⋯N hydrogen bonds; their mean planes are separated by 0.292 (6) Å. Weak C—H⋯Br interactions involving all of the remaining H atoms tie the cations and anions together into sets of interpenetrating sheets. The title compound is isostructural with its iodide analogue.

Crystal structure of 2-cyano-1-methyl­pyridinium tetra­fluoro­borate

The asymmetric unit of the title salt, C7H7N2 +·BF4 −, comprises two independent but nearly identical formula units. The solid-state structure comprises corrugated layers of cations and anions, formed by C—H⋯F hydrogen bonding, that are approximately parallel to (010). Further C—H⋯F hydrogen bonding consolidates the three-dimensional architecture. The sample was refined as a two-component non-merohedral twin.

4-Cyano-1-methyl-pyridinium nitrate.

The title molecular salt, C7H7N2 +·NO3 −, displays an interpenetrating sheet structure parallel to a with each sheet containing nearly coplanar cations and anions, each ion being bisected by a crystallographic mirror plane. C—H⋯O hydrogen bonds involving both ring and methyl H atoms in addition to cation–cation C—H⋯N hydrogen bonds (ring H to cyano N) serve to link the sheets together. In each set of parallel layers, the cations and anions stack with short distances of 3.094 (2) (between aligned nitrate N and pyridine N atoms) and 3.057 (2) Å (between a nitrate O atom and the ring centroid). This motif is strikingly similar to the one that features in the isomeric salt 2-cyano-1-methylpyridinium nitrate.

2-Cyanoanilinium iodide

In the title compound, C7H7N2 +·I−, the cation is located on a site of 4mm symmetry and is thus disordered about the fourfold axis so that there are two perpendicular orientations of the six-membered ring and four rotational orientations of the {–NH3 +} group. In the crystal, there are two layers perpendicular to the c axis, each containing iodide ions and the {–NH3 +} portions of the cations, with the remainder of the cations extending outwards from these layers.

4-Cyano­anilinium bromide

In the crystal structure of the title compound, C7H7N2 +·Br−, the cations are associated into inversion dimers through weak pairwise C—H⋯N hydrogen bonds. The dimers further form stepped sheets via weak pairwise C—H⋯N hydrogen bonds. In the sheets, the spacing between the mean planes of the laterally displaced aromatic rings in adjacent dimers is 1.124 (6) Å. Three N—H⋯Br interactions and two weak C—H⋯Br interactions per cation tie the sheets together.

4-Cyano-1-methyl­pyridinium perchlor­ate

The title salt, C7H7N2 +·ClO4 −, crystallizes with alternating cations and anions in wavy sheets, which are formed by a number of C—H⋯O and C—H⋯N hydrogen bonds, lying approximately parallel to (001).