Crystal structures of side products from the synthesis of 2,6-bis(4 H -1,2,4-triazol-4-yl)pyridine: interplay of geometry and intermolecular interaction energies

Abstract During the synthesis of the triazole-based ligand 2,6-bis(4 H -1,2,4-triazol-4-yl)pyridine, two crystalline side products were obtained, N -(6-aminopyridin-2-yl)formamide, and a 1:1 cocrystal consisting of 6-(4 H -1,2,4-triazol-4-yl)pyridin-2-amine ( 2A ) and pyridine-2,6-diamine ( 2B ). Both compounds were characterized by single-crystal X-ray diffraction and analyzed from geometric and energetic perspectives in order to understand the hierarchy of intermolecular interactions and their role in crystal packing. In the first compound, locally centrosymmetric hydrogen bonded dimers are stacked through π⋯π interactions, forming columnar motifs in the crystal packing. In the cocrystal, molecules of 2A form zig-zag columns via π⋯π stacking interactions as the main structural motif in structure. These columns are further connected by strong hydrogen bonds, resulting in layers of columns as the second structural motif of the crystal structure. Molecules of 2B interact both with these columns and with each other through a combination of hydrogen bonds and π⋯π stacking interactions, resulting in a columnar and anisotropic layered structure. Pairwise interaction energy calculations together with geometric analysis emphasize the dominant contribution of hydrogen bonding and π⋯π stacking in the stabilization of both crystal structures.