Coordination compounds valence bond approach

Although the simple valence-bond approach to the bonding in coordination compounds has many deficiencies, it is still useful as a first attempt to explain the structure of many complexes. The reasons why certain ligands force electron pairing will be explored in Chapter 17, but it is clear that high- and low-spin complexes have different magnetic character, and the interpretation of the results of this technique will now be explored. 

Pauling used his valence bond approach to explain differences in magnetic behavior among coordination compounds by use of either 3d or 4d orbitals of the metal ion. Griffith and Orgel developed and popularized the use of ligand field theory, derived from the crystal field theory of Bethe and Van Vleck ° on the behavior of metal ions in crystals and from the molecular orbital treatment of Van Vleck. Several of these approaches are described in Chapter 10, with emphasis on the ligand field theory. 

At least the reader will find here a table highlighting stereochemistry of inorganic compounds. Its starting point is the idea of the correspondence between the coordination polyhedron and the hybridization state of the central atom, given by the valence bonding approach. In spite of all the restrictions laid upon the applicability of this approach, it seems to be helpful for systematization of the experimental data in inorganic chemistry. 

In the following pages, the valence bond theory and the crystal field theory are described very briefly to set more recent developments in their historical context. The rest of the chapter describes the ligand field theory and the method of angular overlap, which can be used to estimate the orbital energy levels. These two supply the basic approach to bonding in coordination compounds for the remainder of the book. 

However, the valence bond theory approach to transition metals has severe limitations. It fails to account for the absorption spectra and magnetic properties of coordination compounds. These and other properties are more satisfactorily explained by crystal field theory or ligand field theory. 

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