Variable temperature (100-295 K) single-crystal X-ray diffraction study of the α-polymorph of glycylglycine and a glycylglycine hydrate

The crystal structures of the a-polymorph of glycylglycine (glygly) and of its hydrate (glygly x 1.5 H2O) were refined by single-crystal X-ray diffraction at 100, 150, 220, and 295 K (glygly) and at 100, 200, 295 K (glygly x 1.5 H2O). The values of the volume thermal expansions of glygly and its hydrate were shown to be larger than for the three polymorphs of glycine. The anisotropy of strain on cooling was analyzed. Despite a smaller bulk thermal expansion measured for glygly, linear strain (both compression and expansion) along the axes of the strain ellipsoids was larger for the structure of glygly, than for the structure of glygly x 1.5 H2O. The contributions of the distortion of the intermolecular hydrogen bonds and of the conformational changes of the zwitter-ions to the lattice strain are considered.