Bases, solvates and salts: new benzimidazole- and pyridine-scaffolded ligands

The intermolecular interactions in the structures of a series of Schiff base ligands have been thoroughly studied. These ligands can be obtained in different forms, namely, as the free base 2-[(2E)-2-(1H-imidazol-4-ylmethylidene)-1-methylhydrazinyl]pyridine, C₁₀H₁₁N₅, 1, the hydrates 2-[(2E)-2-(1H-imidazol-2-ylmethylidene)-1-methylhydrazinyl]-1H-benzimidazole monohydrate, C₁₂H₁₂N₆·H₂O, 2, and 2-{(2E)-1-methyl-2-[(1-methyl-1H-imidazol-2-yl)methylidene]hydrazinyl}-1H-benzimidazole 1.25-hydrate, C₁₃H₁₄N₆·1.25H₂O, 3, the monocationic hydrate 5-{(1E)-[2-(1H-1,3-benzodiazol-2-yl)-2-methylhydrazinylidene]methyl}-1H-imidazol-3-ium trifluoromethanesulfonate monohydrate, C₁₂H₁₃N₆⁺·CF₃O₃S^-·H₂O, 5, and the dicationic 2-{(2E)-1-methyl-2-[(1H-imidazol-3-ium-2-yl)methylidene]hydrazinyl}pyridinium bis(trifluoromethanesulfonate), C₁₀H₁₃N₅²⁺·2CF₃O₃S^-, 6. The connection between the forms and the preferred intermolecular interactions is described and further studied by means of the calculation of the interaction energies between the neutral and charged components of the crystal structures. These studies show that, in general, the most important contribution to the stabilization energy of the crystal is provided by π-π interactions, especially between charged ligands, while the details of the crystal architecture are influenced by directional interactions, especially relatively strong hydrogen bonds. In one of the structures, a very interesting example of the nontypical F...O interaction was found and its length, 2.859 (2) Å, is one of the shortest ever reported.