Molecular orbital-theoretical studies of a dinuclear Fe(II)-Fe(III) complex

A qualitative molecular orbital (MO) model for a dinuclear Fe(II)-Fe(III) c omplex 2, which can be considered as two edge-sharing octahedra, is evaluat ed on the basis of Extended-Huckel (EH) calculations. The MO picture derive d is compared to the MO scheme suggested for a valence-delocalized Fe(II)-F e(III) complex 1 studied recently, which represents two face-sharing octahe dra. This comparison indicates that the iron-iron interaction plays an impo rtant role in 1 while this interaction is weaker in 2. In both molecules va lence delocalization is provided by an in-phase combination of iron-d-orbit als of a-type with non-negligible ligand admixtures. The stronger intermeta l coupling in 1 is mainly caused by the shorter iron-iron distance. (C) 199 9 Elsevier Science S.A. All rights reserved.