Aspects of aqueous iron and manganese (II/III) self-exchange electron transfer reactions

Ab initio methods were applied to the calculation of the reorganization energy A and the electronic coupling matrix element V-AB for the outer-sphere Fe(OH2)(6)(II/III) and Mn(OH2)(6)(II/III) self-exchange electron transfer (ET) reactions. For the Fe case, we find an appreciable effect on V-AB depending on whether the minority spin electron occupies the d(xy) orbital or a mixture of d(xz)/d(yz) orbitals in the Fe-II ion. While these two possible nearly isoenergetic electron accepting states alter the magnitude and distance dependence of V-AB, they do not affect the internal reorganization energy lambda(1) to any significant level. The magnitude and distance dependence of V-AB are found to be strongly dependent on encounter orientation, as expected. V-AB values for corner-to-corner encounter orientations are substantially larger at any given ET distance considered than those for face-to-face encounter orientations. Values of the decay parameter beta are in good agreement with well-accepted values. The adiabaticity criterion is tied to orientation and distance dependence of V-AB.