Conformational polymorphism in cocrystal of pregabalin and octanoic acid.

A cocrystal of pregabalin and octanoic acid shows two phase transitions when temperature is lowered. These transitions were followed using differential scanning calorimetry. Both transitions are single-crystal to single-crystal allowing the study of these transitions using single-crystal X-ray diffraction at different temperatures. The crystal structures of the different forms were determined. Negative thermal expansion is observed along the shortest unit-cell axis in form III. Ultimately, subsequent transitions to form II and form I lead to positive thermal expansion in every principal strain axis.