Thermoanalytical behaviour of the captopril- cobalt(II) complex

Captopril (H2L) reacts with cobalt(II) in aqueous solution at a neutral pH forming a deep red complex. The reaction rate depends on the temperature, pH, metal ion and ligand concentrations. A solid compound precipitates by acidification of the solution. The chemical, potentiometric, and spectroscopic analyses of the solid complex give the simplest formula, Co(HL)2·H2O, and suggest that the sequence of the bonds is S-Co-S, with the carboxylic group of the ligand remaining uncoordinated. The thermal behaviour of the captopril and its cobalt complex was studied by thermogravimetry, differential thermal analysis and differental scanning calorimetry in dynamic nitrogen and oxygen atmospheres.