Cytotoxic Pt(IV) and Ru(II) complexes containing a biologically relevant edda-type ligand: A comparative study of their thermal properties

Abstract

The thermal behaviour of a Pt(IV) and a Ru(II) complex coordinated to dibutyl (S,S)-α,α′-(1,2-ethanediyldiimino)biscyclohexanepropanoate was investigated using thermogravimetry (TG) and differential scanning calorimetry (DSC). The study included an investigation of the thermal decomposition of these complexes in the temperature range of 30 to 590°C and an evaluation of the activation energy for the first decomposition steps. For both metal complexes, broad DSC peaks indicated complex thermal transformation processes. The two-step decomposition of the Pt(IV) complex started at 175 and ended at about 418°C, leaving elemental platinum as the final residue. On the other hand, the Ru(II) analogue decomposed in three stages. Thermal degradation was evident beginning at 144°C and suggested the decomposition of a coordinated ligand as the dominant process. For this complex, the proposed final residue was RuO2. Kinetic parameters for the first decomposition step were obtained by means of the multi-heating rates method, in this case the Kissinger-Akahira-Sunose (KAS) method. The mean activation energy calculated for 0.2 < α < 0.8 were 122.0 kJ mol-1 for the Pt(IV) and 118.9 kJ mol-1 for the Ru(II) complex and decreased constantly, a characteristic of a multi-step process.