Tape and layer structures in cocrystals of some di- and tricarboxylic acids with 4,4′-bipyridines and isonicotinamide.: From binary to ternary cocrystals

Linear, zigzag tapes and flat, corrugated sheet structures are described in binary cocrystals 1-9 of some di- and tricarboxylic acids with 4,4'-bipyridine bases and isonicotinamide. Carboxylic acid. pyridine O-H center dot center dot center dot N, its proton transfer form N+-H center dot center dot center dot O-, carboxamide dimer N-H center dot center dot center dot O, and extended motifs are present in these crystal structures. Our results show modular expansion of carboxylic acid dimer in neutral cocrystals with pyridine type bases. Even as the structures of these aggregates can be understood from the molecular constituents in a straightforward manner, the nature of acid. pyridine synthon, i.e. neutral or ionic, is difficult to anticipate from their Delta pK(a) values. We modify the Delta pK(a) (pK(a) conjugate acid of pyridine base - pK(a) carboxylic acid) rule in COOH - pyridine cocrystals: Delta pK(a) < 0 results in neutral O-H center dot center dot center dot N hydrogen bond; 0 < Delta pK(a) < 3.75 have an intermediate O-H center dot center dot center dot N/N+-H center dot center dot center dot O- H bond character; and Delta pK(a) > 3.75 results in proton migration to the ionic interaction N+-H center dot center dot center dot O-. Proton transfer results in the assembly of a supramolecular 3-connected node of cyclohexane tricarboxylate and these anions form chair cyclohexane or parquet grid sheets in 10 and 11. The length of bipyridinium cation plays a role in the overall structure. A novel approach to three-component adducts is crystallization of 1,3cis,5cis-cyclohexane tricarboxylic acid with 4,4'-bipyridine and 4,4'-bipyridine-N-oxide bases of different strengths, which results in a ternary cocrystal 12 sustained via O-H center dot center dot center dot N and O-H center dot center dot center dot O- hydrogen bonds.