Molecular orbital models, solid-state complexes

The structural strengths of the hybridization model were combined with the electronic strengths of the crystal-field model in a molecular-orbital model albeit with the loss of the simplicity of the earlier models. The essential aspects of this MO model will be discussed in Chapter 1. The key point here is that, if one wishes to understand the electronic structure of metal-coordination compounds, one need go beyond the Lewis model of two-center-two-electron bonds. It should be obvious, then, that this is also a requirement for organometallic complexes, metal clusters and extended solid-state systems containing metal atoms. 

An X-ray atomic orbital (XAO) [77] method has also been adopted to refine electronic states directly. The method is applicable mainly to analyse the electron-density distribution in ionic solids of transition or rare earth metals, given that it is based on an atomic orbital assumption, neglecting molecular orbitals. The expansion coefficients of each atomic orbital are calculated with a perturbation theory and the coefficients of each orbital are refined to fit the observed structure factors keeping the orthonormal relationships among them. This model is somewhat similar to the valence orbital model (VOM), earlier introduced by Figgis et al. [78] to study transition metal complexes, within the Ligand field theory approach. The VOM could be applied in such complexes, within the assumption that the metal and the... 

This chapter is a continuation of the last in that the orbitals of our other molecular building block, a square planar ML4 complex, are developed. This is a little more complicated than the octahedral case however, we shall need to use the orbitals of both extensively in subsequent chapters. From the octahedral and square planar splitting patterns, a generalized bonding model can be constructed for transition metal complexes. This, In turn, leads to the topic of electron counting. Finally, we examine one distortion that takes a square planar molecule to a tetrahedron and two examples from the solid state. 

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