Groth's original concomitant polymorphs revisited

The search for the third concomitant polymorphic form γ of 1,3-bis(m-nitrophenyl)urea that was described in 1899, but not reported in more recent papers, has revealed a new polymorphic form, δ, and a monohydrate form of the material in addition to its already known α and β forms. It is suggested that the monohydrate is actually the literature-reported γ form. Both new forms have been characterized and compared to α and β forms by a variety of methods including thermal methods, FT-IR, and cross polarization/magic angle spinning (CPMAS) NMR spectroscopy, single-crystal X-ray structure determination, and lattice energy calculations.