A search for predictable hydrogen-bonding synthons in cocrystallization of unusual organic acids with a bent dipyridine

A bent dipyridyl compound, 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo), was employed to crystallize with 1,4-cyclohexanedicarboxylic acid (H(2)chdc), hydroquinone, citric acid (H(4)ca center dot HO), barbituric acid, and ferrocene dicarboxylic acid (H(2)Fc) under general conditions, affording binary cocrystals [(H(2)chdc)center dot(4-bpo)] (1), [(hydrquinone)center dot(4-bPO)(2)] (2), [(H(4)ca)center dot(4-bpo)] ,(3), [(barbituric acid)center dot(4-bpo)] (4), and [(HFc)center dot(H-4-bpo)] (5) in high yield. X-ray single-crystal structures of these compounds 2 reveal that a supramolecular synthon [R-2(2)(7)] containing classical O-H center dot center dot center dot N and weak C-H center dot center dot center dot O interactions, usually observed in organic cocrystals of carboxylic acid and heterocyclic base, is again involved in constructing the hydrogen-bonding networks of 1, 3, and 5. Its ionic analogous synthon [consisting of strong N-H center dot center dot center dot O and weak C-H center dot center dot center dot O, R-2(2) (7)] also appears in the partly charge transfer salt 5. For 2, only hydroxyl of the hydroquinone component can act as the hydrogen-bonding contributor, giving a strong O-H center dot center dot center dot N bond with 4-bpo. Multiple hydrogen-bonded donating/accepting sites in compound 3 fulfill the formation of new Z, supramolecular patterns. For 4, another heterosynthon ring [containing strong N-H center dot center dot center dot N and weak C-H center dot center dot center dot O, R-2(2)(7)] is formed due to the presence of the imide functional group. As a consequence, robust hydrogen-bonding interactions in these compounds afford Z, diverse 2-D waved or planar layers (1 or 4), I-D extended tape (2), 3-D net (3), and I-D molecular-box type (5) supramolecular architectures. Thermal stability of these compounds has been investigated by thermogravimetric analysis (TGA) of mass loss.