Concomitant polymorphism in the pseudo-peptide Me2N-pC6H4C(O)-Phe-OEt

Pseudo-peptide Me2N-pC6H4C(O)-Phe-OEt (1) exhibits two polymorphic forms which crystallizes in non-centrosymmetric space groups, monoclinic 1m (P21) and orthorhombic 1o (P212121). Both forms occur concomitantly or as a pure phase depending on the solvent of crystallization. Single crystal X-ray diffraction revealed equivalent two-dimensional layers in both 1m and 1o, the different modes of layer stacking are caused by CH⋯π interactions specific for each polymorph. Both solid forms are transparent in visible spectral region, with different absorbance patterns in lower UV region. Thermodynamic relations between two polymorphs were unambiguously established using room-temperature competitive slurry experiments, mechanochemistry and heating.