Phase polymorphism of [Co(DMSO)6](ClO4)2 studied by differential scanning calorimetry

Five solid phases of [Co(DMSO)6](ClO4)2 have been detected by differential scanning calorimetry (DSC). Specifically, the phase transitions were detected between the following solid phases: metastable KIII ↔ overcooled K0 at TC4 = 329 K, stable KIb → stable KIa at TC3 = 350 K, metastable KII ↔ overcooled K0 at TC2 = 363 K and stable KIa → stable K0 at TC1 = 377 K. The title compound melts gradually in three steps with final melting point at Tm = 495 K. From the entropy changes of the melting point and phase transitions it can be concluded that phases K0 and overcooled K0 are orientationally dynamically disordered phases. Stable phases KIa, KIb and metastable phase KIII are ordered solid phases. Metastable phase KII is probably a solid phase with a high degree of orientational dynamical disorder.