Phase polymorphism and thermal decomposition of hexadimethylsulphoxidemagnesium(II) chlorate(VII)

Abstract

Differential scanning calorimetry (DSC) measurements were performed over the temperature range 93–480 K and three enantiotropic (at 323, 409, and 461 K) and one monotropic (at 271 K) phase transitions were detected. Thus, four solid phases (three of them stable and one metastable) and one liquid phase were found. It was concluded, from the entropy change (ΔS) values of these phase transitions that two of them are stable rotational phases and two are crystalline phases (one stable and one metastable). The thermal decomposition of [Mg((CH3)2SO)6](ClO4)2, which was studied using thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA), takes place in two main stages. The gaseous products of the decomposition were identified on-line by a quadruple mass spectrometer (QMS). In the first stage, which starts just above ca. 432 K, the compound loses two dimethylsulphoxide (DMSO) molecules per one formula unit. In the second stage (502–673 K) [Mg(DMSO)4](ClO4)2 decomposes explosively and Cl2, O2, H2, and MgSO4 are finally produced.