Conformation-Directed Hydrogen-Bonding in meta-Substituted Aromatic Ureadicarboxylic Acid: A Conformationally Flexible U‑Shaped Building Block

Crystal structures of U-shaped aromatic ureadicarboxylic acid possessing two carboxy moieties at meta-positions of phenyl rings were investigated. It afforded cocrystals with dipyridyl derivatives. In addition to the U-shaped conformation obtained by recrystallization from methanol, another three types of U-shaped conformations were found in the crystal structure of the cocrystals. The direction of H-bonding was fixed based on the relative geometry of two carboxy moieties in the resulting conformations. Depending on these conformations, triple helices with one-dimensional water channels, infinite cross-belt, and step-like structures were generated via H-bonding between the carboxy and the pyridyl moieties. Methanol solvate was obtained for the cocrystal with 1,4-di­(pyridine-4-yl)­benzene which showed different U-shaped conformation of urea dicarboxylic acid from that involved in the cocrystal free of methanol.