Study of the kinetics of electrochemical reactions by thin-layer voltammetry II. Electro-oxidation of platinum(II) complexes

Studies are reported which indicate that the electro-oxidation of Pt(II) complexes of the series Pt(NH3)m(NO2)4-mm−2 and Pt(NH3)mCl4-mm−2 is sharply accelerated by free chloride, and that inclusion of chloride in the Pt(IV) product occurs. In the absence of free chloride, the reactivity of these complexes is greatly decreased but increases with the number of halide ligands in the coordination sphere. The reactions are stereospecific, the two entering ligands having the trans-configuration and the other four ligands retaining the orientation in the Pt(II) starting material. PtIIL4+X+C1− → trans-PtIVL4XCI+2e− PtIIL3C1+2 H2 → trans-PtIVL3CI(H2O)2+2e− X=H2O or C1− Oxidation in chloride media of positively charged Pt(II) complexes leads to inclusion of two chloride (X=Cl−) whereas oxidation of negative complexes tends toward inclusion of one water and one chloride (X=H2O). The results obtained appear consistent with the suggestion that the electrooxidation of Pt(II) proceeds through an intermediate complex adsorbed at the electrode surface through a bridging halogen.