A study of phase transitions in cadmium perchlorate hexahydrate (Cd(ClO4)2.6H2O) by adiabatic calorimetry and infrared spectroscopy.

Abstract

A calorimetric study of Cd(ClO4)2.6H2O from 20 to 345 K shows 3 phase transformations, at 124.8, 238.45, and 271.62 K. IR spectra indicate that the low-temp. structure (below 124.8 K) contains 1 type of [Cd(OH2)6]2+, of symmetry C3 or C3v, and 2 types of ClO4-, both strongly distorted from tetrahedral symmetry. There appears to be some disorder in this phase. The sharp transition at 124.8 K leads to major spectral changes, which indicate that H bonding is weakened, distortion of the perchlorate ions is diminished, and [Cd(OH2)6]2+ symmetry is increased to D 3d. The more gradual phase transition at 238.45 K involves no observable IR spectroscopic changes and may correspond to an increase in ClO4- disorder. The very sharp transition at 271.6i K involves only very minor changes in the IR spectra and may involve an increased disorder of the [Cd(OH2)6]2+ units.