Molecular crystals of 2-methyl-1H-benzo[d]imidazole and pyridine-2,6-dimethanol with chloranilic, trimesic and gallic acid

Crystallization experiments of 2-methyl-1H-benzo[d]imidazole (MBI) and pyridine-2,6- dimethanol (PDM) with chloranilic (CLA), trimesic (TMA) and gallic acid (GA) yielded a total of ten multicomponent molecular crystals in salt form, i.e., MBI:CLA (1), 2MBI:CLA:2H2O (2), 2MBI:CLA:3H2O (3A), 2MBI:CLA:3H2O (3B), 2MBI:CLA:4H2O (4), MBI:TMA (5), MBI:GA:3.4H2O (6), PDM:CLA (7), PDM:CLA:H2O (8), and 2PDM:CLA (9), of which compounds 3A and 3B are polymorphs. Characteristic for the crystal structures of all compounds except for 7 is the presence of heterosynthons formed between the molecular components by charge-assisted N−HMBI/PDM⋯OCLA/TMA/GA hydrogen bonds, which are mostly bifurcated. In compound 7, the positively charged N−H groups are involved in the formation of PDM-PDM homodimers interacting through N−HPDM⋯OPDM hydrogen bonds. The series of compounds having 2:1 MBI/PDM:CLA ratio (2, 3A, 3B, 4 and 9) comprise trimeric molecular units of the composition MBI-CLA-MBI or PDM-CLA-PDM, respectively, based on charge-assisted bifurcated N−H⋯O hydrogen bonds. Despite the directionality of these interactions, the units have certain flexibility consisting in mutual bending of the aromatic ring planes and are considered interesting building blocks for crystal engineering purposes. Except for compound 9, all crystal structures exhibit π⋯π interactions involving the positively charged benzimidazolium and pyridinium rings of protonated MBI and PDM and/or the π-delocalized sections in the organic anions. The water molecules in hydrates 2, 3A, 3B, 4, 6 and 8 exercise mostly crystal lattice stabilizing functions by interconnecting the synthons established among the organic components. Hirshfeld surface and fingerprint analysis revealed that O⋯H/H⋯O interactions and van der Waals contacts are dominant in conjunct with Cl⋯H/H⋯Cl contacts in the compounds derived from CLA.