Conformation-Directed Hydrogen-Bonding in <i>meta</i>-Substituted Aromatic Ureadicarboxylic Acid: A Conformationally Flexible U‑Shaped Building Block
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Abstract
Crystal
structures of U-shaped aromatic ureadicarboxylic acid possessing two
carboxy moieties at <i>meta</i>-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