Application of valence bond principles to the descriptions of main group and transition metal shapes

Describing the shapes of inorganic compounds with molecular mechanics can be a difficult task. Problems arise with some of the more complex shapes that are seen as well as the large numbers of parameters that are needed to describe compounds from all areas of the periodic table. Valence bond theory can be used to help solve these problems. From the overlap of hybrid orbitals can be derived new, hybridization-dependent, potential energy functions for describing angle bending potentials. These functions describe well the shapes of non-hypervalent molecules. They can also be extended to describe the shapes of hypervalent main group compounds by incorporating the concept of resonance into a molecular mechanics framework. With this it is possible to model not only equilibrium geometries of hypervalent main group compounds, but also fluxtional processes such as ligand site exchange. The application of the hybridization-based potential energy functions and resonance structure model to transition metals is accomplished after establishing a set of rules for determining hybridizations of transition metal complexes. The model is remarkably accurate for describing complex shapes that are found in transition metal hydrides and alkyls.