Spectroscopic studies of metal complexes containing π-delocalized sulfur ligands. Mössbauer and kinetic studies of iron(II) and iron(III) complexes of the antitumor agent 2-formylpyridine thiosemicarbazone

Abstract

Mössbauer studies on the Fe(II) and Fe(III) complexes of 2-formylpyridine thiosemicarbazone (FPT) showed the complexes to be low spin and provided evidence of the reducing character of the ligand. In addition, kinetic measurements of the Fe(III) complex reduction by the ligand gave an expression for the initial rate of the type v i = k′A + k″AB, in which A stands for the concentration of the Fe(III) complex and B for the concentration of the reducing agent. From this equation one may infer the coexistence of two mechanisms, one expressed by the first term and occurring even in the absence of FPT. For the second term we propose an inner sphere mechanism in which the ligand is the reducing agent.