Bond orders in metal-metal interactions through electron density analysis

The metal-metal bond is central in the chemistry of polymetallic complexes. Many structural investigations, both experimental and theoretical, have been carried out with the purpose of understanding this interaction in more detail and of being able to predict the stereochemistry of these molecules. Among these studies, increasing importance is given to electron density analysis. Originally, only deformation densities were analysed, but it became clear that more sophisticated theories were necessary to appreciate the subtleties of these elusive chemical bonds. Thus, the quantum theory of atoms in molecules, electron delocalisation indices, the electron localisation function and the domain averaged Fermi hole density are nowadays used to characterise metal-metal bonds. The major results reported in the literature in the past few years are carefully reviewed in this chapter. © 2010 Springer-Verlag Berlin Heidelberg.