Redox-Induced Changes in the Geometry and Electronic Structure of Di-μ-oxo-Bridged Manganese Dimers

Abstract

Broken-symmetry approximate density functional theory has been used to investigate the electronic and structural properties of the complex Mn2O2(NH3)8z+ in three distinct oxidation states, Mn2IV/IV (z = 4), Mn2III/IV (z = 3) and Mn2III/III (z = 2). In Mn2IV/IV the metal-based electrons are almost completely localized on one center or the other, and occupy the single-ion orbitals derived from the t2g subset of the parent octahedron. The additional two electrons in Mn2III/III enter dz2 orbitals aligned along the Mn−Nax axis, resulting in a significant elongation of these bonds. Both dx2-y2 and dz2 orbitals transform as a1 in C2v symmetry, and so electron density can be transferred from the dz2 orbital on one center to the dx2-y2 orbital on the other. In the symmetric dimers, Mn2IV/IV and Mn2III/III, the energetic separation of the dz2 and dx2-y2 orbitals is sufficiently large to prevent significant delocalization of the metal-based electrons along this pathway. In contrast, a combination of low-spin polariz...