Four-nuclear mixed-valence vanadium clusters: divergence of phenomenological and molecular orbital models Original Research Article

The electronic structure of four-nuclear vanadium cluster representing the well-known vanadyl pyrophosphate catalytic system is studied on the basis of model Hamiltonian and semi-empirical molecular orbital approaches. The possible charge redistribution resulting from the vibronic interaction is analyzed for different mixed-valence combinations of VV and VIV. The adiabatic surfaces are calculated in the space of normal modes built from the VO vibrations of vanadyl groups. It is shown that in some cases the two approaches may lead to different localization patterns of excess electron(s). The molecular orbital model is a more adequate way to describe the structural features of real compounds, whereas the phenomenological model allows to analyze the qualitative influence of the different electronic interactions.