Melting processes and thermal decompositions of [Ca(H2O)4](ClO4)2 and [Ca(NH3)6](ClO4)2 were studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). The gaseous products of the decomposition were on-line identified by a quadruple mass spectrometry (QMS).
In both compounds the processes of loss of the ligands start at ca. 340–350 K and continue up to ca. 600 K. Tetraaquacalcium perchlorate dissolves in own coordination water (melts) at T m=350 K. The decomposition of the sample proceeds in three main stages. In stage I (351–602 K) dehydration of [Ca(H2O)4](ClO4)2 to anhydrous Ca(ClO4)2 undergoes in two steps, in which consecutively 2/4 and 2/4 of all H2O molecules are liberated. In stage II (602–701 K) anhydrous Ca(ClO4)2 has one solid-solid phase transition at T c=619 K and then melts at T m=689 K. Stage III (above 700 K) is connected with decomposition of melted Ca(ClO4)2 to oxygen and solid CaCl2. The decomposition of the [Ca(NH3)6](ClO4)2 proceeds also in three main stages. In stage I (341–601 K) deamination of [Ca(NH3)6](ClO4)2 to Ca(ClO4)2 undergoes in two steps, in which consecutively 3/6 and 3/6 of all NH3 molecules are liberated. Stages II and III (601–868 K) are exactly the same as they were observed for [Ca(H2O)4](ClO4)2.