Variable-temperature and variable-pressure studies of small-molecule organic crystals

Several examples of the comparative variable- temperature and variable- pressure studies of the small- molecule organic crystals are discussed. Selected systems represent the crystals with nonspherical flexible molecules / molecular fragments and with different types of intermolecular interactions, ranging from van der Waals interactions to hydrogen bonds of various types ( OH ... O, NH ... OH, NH ... O= C). A special attention is payed to the studies of solid drugs ( polymorphs of paracetamol), amino acids ( polymorphs of glycine, L- serine, D, L- serine), and dipeptides ( glycilglycine and glycilglycine hydrate) by structural, spectroscopic and calorimetric techniques. The anisotropy of structural distortion within the range of stability of the same phase, as well as the phase transitions induced by changes in temperature or pressure are discussed.