Based On Hydrogen Bonding Synthon Competition And Prediction

2,5-Bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo) and its 4-N-donor analogue 2,5-bis(4-pyridyl) -1,3,4-oxadiazole (4-bpo), are introduced to synthesize a series of binary cocrystals with different carboxylic acids from rigid aromatic to flexible aliphatic species. In contrary to classical linear dipyridyl building blocks, the bent bpo bases can form robust hydrogen-bonding syn-thons with these organic acids and produce well-defined cocrystallizing supramolecular compounds in considerable high yields.The preparation and X-ray structures of six 1:1 molecular cocrystals including [phthalic acid]- [3-bpo] (1), [phthalic acid]-[4-bpo] (2), [isophthalic acid]-[3-bpo] (3), [isophthalic acid]-[4-bpo] (4), [terephthalic acid]-[3-bpo] (5) and [terephthalic acid]-[4-bpo] (6), are described. A supramolecular synthon I [R22(7)] containing classical O-H…N and weak C-H…O interactions, usually observed in organic cocrystals of carboxylic acids with other heterocyclic bases, is again shown to be involved in constructing most of these hydrogen-bonding networks. Melting points of cocrystals 1-6 are mainly correlated with the nature of acid component and crystal packing. Thermogravimetric analysis (TGA) of mass loss for six compounds has been shown to correlate with the strength of hydrogen bonds in the packing fraction.Bpos were applied to crystallize with trimesic and pyromellitic acid (H3TMA and H4BTA), affording three new cocrystals [(H3TMA)(3-bpo)]-DMF (7), [(H3TMA)-(4-bpo)] (8), [(H4BTA)-(3-bpo)]-2H2O (9) and apartly charge-transfer salt [(H2BTA)./3-(H-4-bpo)-(H4BTA)1/2] H2O (10) under general conditions. Pyromellitic dihydrazide (11) was obtained during the attempt of attaining a cocrystal of 4-bpo and H4BTA by hydrothermal synthesis. X-ray single-crystal diffraction studies reveal that supramolecular synthon I [R22 (7)] is again testified to be involved in constructing the binary hydrogen-bonding networks of 7-10, in which the het-eromeric intermolecular interactions are often utilized as effective synthetic tools to provide a significant portion of the stabilization energy of molecular crystals. Thermal stability of cocrystals 7-10 has been investigated by TGA of mass loss.The preparation and X-ray structures of six 1:1 stoichiometric cocrystals were discussed in...