Crystal structures of the hexa-fluorido-phosphate salts of the isomeric 2-, 3- and 4-cyano-1-methyl-pyridinium cations and determination of solid-state inter-action energies.

The synthesis and crystal structures of the isomeric mol-ecular salts 2-, 3- and 4-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C7H7N2+·PF6-, are reported. In 2-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C-H⋯F hydrogen bonds form chains extending along the c-axis direction, which are associated through C-H⋯F hydrogen bonds and P-F⋯π(ring) inter-actions into stepped layers. For 3-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, corrugated sheets parallel to [001] are generated by C-H⋯F hydrogen bonds and P-F⋯π(ring) inter-actions. The sheets are weakly associated by a weak inter-action of the cyano group with the six-membered ring of the cation. In 4-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C-H⋯F hydrogen bonds form a more open three-dimensional network in which stacks of cations and of anions are aligned with the b-axis direction. Dispersion-corrected density functional theory (DFT-D) calculations were carried out in order to elucidate some of the energetic aspects of the solid-state structures. The results indicate that the distribution of charge within a mol-ecular ionic cation can play a large role in determining the strength of a cation-anion inter-action within a crystal structure. Crystals of 2-cyano-1-methyl-pyridinium hexa-fluorido-phosphate are twinned by a 180° rotation about the c* axis. The anion in 3-cyano-1-methyl-pyridinium hexa-fluorido-phosphate is rotationally disordered by 38.2 (1)° in an 0.848 (3):0.152 (3) ratio.

Crystal structure of 2-cyano-1-methyl-pyridinium tetra-fluoro-borate.

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.

Crystal structure of 2-cyano-1-methyl-pyridinium perchlorate.

The asymmetric unit of the title salt, C7H7N2 (+)·ClO4 (-), comprises two independent formula units. The solid-state structure comprises corrugated layers of cations and of anions, approximately parallel to (010). The supra-molecular layers are stabilized and connected by C-H⋯O hydrogen bonding to consolidate a three-dimensional architecture. A close pyridin-ium-perchlorate N⋯O contact [2.867 (5) Å] is noted. The crystal was refined as an inversion twin.

Crystal structure of 2-cyano-1-methyl-pyridinium bromide.

In the title mol-ecular salt, C7H7N2 (+)·Br(-), all the non-H atoms lie on crystallographic mirror planes. The packing consists of (010) cation-anion layers, with the cations forming dimeric units via very weak pairwise C-H⋯N inter-actions. Weak C-H⋯Br inter-actions link the cations to the anions.

4-Cyano-1-methyl-pyridinium perchlor-ate.

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).

3-Cyano-N-methylpyridinium perchlorate.

In the crystal of the title mol-ecular salt, C7H7N2 (+)·ClO4 (-), the components are linked by C-H⋯O and C-H⋯N inter-actions, generating zigzag chains running parallel to [100].

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 inter-actions.

2-Cyano-anilinium iodide.

The solid-state structure of the title salt, C7H7N2 (+.)I(-), consists of cation-anion sheets lying parallel to (110), with the components linked by N-H⋯I hydrogen bonds.

4-Cyano-1-methyl-pyridinium nitrate.

The title mol-ecular salt, C7H7N2 (+)·NO3 (-), displays an inter-penetrating sheet structure parallel to a with each sheet containing nearly coplanar cations and anions, each ion being bis-ected 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) Š(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-methyl-pyridinium nitrate.

4-Cyano-anilinium bromide.

In the crystal structure of the title compound, C(7)H(7)N(2) (+)·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 inter-actions and two weak C-H⋯Br inter-actions per cation tie the sheets together.

4-Cyano-anilinium iodide.

In the title compound, C(7)H(7)N(2) (+)·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 {-NH(3) (+)} group. In the crystal, there are two layers perpendicular to the c axis, each containing iodide ions and the {-NH(3) (+)} portions of the cations, with the remainder of the cations extending outwards from these layers.

4-Cyano-1-methyl-pyridinium bromide.

In the crystal of the title mol-ecular salt, C(7)H(7)N(2) (+)·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 inter-actions involving all of the remaining H atoms tie the cations and anions together into sets of inter-penetrating sheets. The title compound is isostructural with its iodide analogue.

4-Cyano-1-methyl-pyridinium iodide.

In the crystal structure of the title compound, C(7)H(7)N(2) (+)·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 inter-actions between adjacent dimers generate a layer lying parallel to (10-1). The remaining H atoms form C-H⋯I inter-actions, which link the layers into a three-dimensional structure.

2-Cyano-1-methyl-pyridinium nitrate.

In the title compound, C(7)H(7)N(2) (+)·NO(3) (-), all atoms except the methyl H atoms lie on a crystallographic mirror plane. The inter-layer 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 inter-actions link cations within each layer. Anion-π inter-actions with the cations assist in binding the layers together.