A Search for Predictable Hydrogen-Bonding Synthons in Cocrystallization of Unusual Organic Acids with a Bent Dipyridine

Abstract

A bent dipyridyl compound, 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo), was employed to crystallize with 1,4-cyclohexanedicarboxylic acid (H2chdc), hydroquinone, citric acid (H4ca·H2O), barbituric acid, and ferrocene dicarboxylic acid (H2Fc) under general conditions, affording binary cocrystals [(H2chdc)·(4-bpo)] (1), [(hydroquinone)·(4-bpo)2] (2), [(H4ca)·(4-bpo)] (3), [(barbituric acid)·(4-bpo)] (4), and [(HFc)·(H-4-bpo)] (5) in high yield. X-ray single-crystal structures of these compounds reveal that a supramolecular synthon [ (7)] containing classical O−H···N and weak C−H···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···O and weak C−H···O, (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···N bond ...