Crystal engineering using 4,4′-bipyridyl with di- and tricarboxylic acids

The X-ray structures of four co-crystals of 4,4′-bipyridyl (Bipy) with two dicarboxylic acids and two tricarboxylic acids are described. A coupling (I) involving O–H⋯N and C–H⋯O interactions, previously seen in co-crystals of carboxylic acids with other heterocyclic bases, is again shown to be involved in the formation of supramolecular structures. Bipy with isophthalic acid, 1,4-naphthalenedicarboxylic acid and 1,3,5-cyclohexane-tricarboxylic acid forms 1:1 complexes. Tapes of acid:base components are formed via coupling I; these tapes extend to form supramolecular sheets via O–H⋯O and/or C–H⋯O interactions. With tricarballylic acid, a co-crystal with stoichiometry 3:2 (acid:base) is generated, with a four-acid-four-base cyclic motif (involving coupling I) as the elementary supramolecular unit. Two previously reported co-crystals of Bipy with trimesic acid and 2,5-di-n-hexylterephthalic acid are also discussed, as well as a CSD search for coupling I in mono-and poly-carboxylic acid/Bipy complexes.