Structural Diversity in 1,3-Bis(<i>m</i>‑cyanophenyl)urea

Hydrogen
bonding between 1,3-bis ureas is a commonly used motif
in the assembly of supramolecular structures such as gels, capsules
and crystals. The title compound, 1,3-bis­(m-cyanophenyl)­urea
(mCyPU), has previously been shown to crystallize in
both an anhydrous and monohydrate phase (α and H–I).
An expanded search for polymorphs and cocrystals of mCyPU revealed a much greater diversity of solid forms including three
additional polymorphs (β, δ, ε), a second hydrate
(H–II) and two cocrystal phases with dimethyl sulfoxide and
triphenylphosphine oxide. Analysis of the single crystal structures
obtained in this study shows that the typical 1-dimensional H-bonding
between 1,3-bis urea groups is disrupted by the presence of other
H-bond acceptors including cyano, water, sulfoxide and phosphine oxide
functionalities. Re-examination of α-mCyPU additionally
showed both blade and plate-like morphologies could be obtained from
different growth solvents, with crystals of the latter morphology
exhibiting a grain boundary migration prior to melting.