Phase Polymorphism, Molecular Motions and Structural Changes in [Cr(NH3)6](ClO4)3

Abstract

A phase transition in [Cr(NH3)6](ClO4)3 at Th c = 293.5 K (on heating) and Tc c = 293.0 K (on cooling) was determined by differential scanning calorimetry. The temperature dependences of the full width at half maximum of the bands connected with ρr(NH3)F1u and δd(ClO)E modes suggest that the discovered phase transition is not connected with drastic changes in the speed of reorientational motions of the NH3 ligands nor the ClO4 − anions. Temperature dependence of the FT-FIR spectra and the diffraction patterns show that the discovered phase transition is caused by a change in the crystal structure.