Hydrogen bonding in two benzene-1,2-diaminium pyridine-2-carboxylate salts and a cocrystal of benzene-1,2-diamine and benzoic acid.

The isostructural salts benzene-1,2-diaminium bis(pyridine-2-carboxylate), 0.5C6H10N22+·C6H4NO2-, (1), and 4,5-dimethylbenzene-1,2-diaminium bis(pyridine-2-carboxylate), 0.5C8H14N22+·C6H4NO2-, (2), and the 1:2 benzene-1,2-diamine-benzoic acid cocrystal, 0.5C6H8N2·C7H6O2, (3), are reported. All of the compounds exhibit extensive N-H...O hydrogen bonding that results in interconnected rings. O-H...N hydrogen bonding is observed in (3). Additional π-π and C-H...π interactions are found in each compound. Hirshfeld and fingerprint plot analyses reveal the primary intermolecular interactions and density functional theory was used to calculate their strengths. Salt formation by (1) and (2), and cocrystallization by (3) are rationalized by examining pKa differences. The R22(9) hydrogen-bonding motif is common to each of these structures.