Activation Energy of Electron Transfer between a Metal Electrode and Reagents of Nonspherical Form and Complicated Charge Distribution. Cr(EDTA) Complexes

An approach is suggested in order to investigate the mechanism of interfacial electron-transfer processes with reagents of nonspherical form and complicated charge distribution. Chelate chromium(III) ethylenediaminetetraacetate (EDTA) complexes are regarded as a good model system. A series of SCF quantum chemical calculations at the ZINDO/1 level were performed for the systems Cr(EDTA)(H2O)n- (n = 0, 1, 2, 3, and 4). A quinquedentate complex Cr(EDTA)H2O- was found to be energetically more favorable compared to Cr(EDTA)-. The interaction of Cr(EDTA)- with a cadmium electrode (modeled as a 19-atomic planar cluster) was investigated as well. The analysis of both the potential energy surfaces and the partial charge transfer allows the explanation of the absence of “specific” interaction between Cr(EDTA)- complexes and mercury-like metals observed experimentally. A way to estimate the inner-sphere contribution (Ein) to reorganization energy is proposed. The inner-sphere asymmetry (nonequality of Ein values for...