Phase transition and thermal decomposition of [Al(DMSO)₆]Cl₃

Abstract

Phase transition and thermal decomposition of hexadimethylsulfoxidealuminium chloride were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA). The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). In the temperature range of 95–300 K, [Al(DMSO)₆]Cl₃ indicates one phase transition at T ^h_c =244.96 K (on heating) and at T ^c_c =220.87 K (on cooling). Large thermal hysteresis of the phase transition (∼24 K) indicates its first order character. Large value of transition entropy (ΔS≈40 J mol⁻¹ K⁻¹) suggests its configurational character. Thermal decomposition of the title compound proceeds in four main stages. In the first stage, which starts just above ca. 300 K, the compound loses two DMSO molecules per one formula unit and undergoes into [Al(DMSO)₄]Cl₃. In the second stage, the next three DMSO ligands are released and simultaneously decomposed. The third stage, which continues up to ca. 552 K, is connected with a loss of the last DMSO ligand and the formation of AlCl₃. In the fourth stage AlCl₃ reacts with carbon monoxide that originates from the decomposition of DMSO, and first aluminium oxychloride and next solid Al₂O₃ plus carbon are created.