Ligand field theory classification

Our conclusion today is that ligand-field theory is essentially the one-electron approximation used for the classification of the energy levels of inorganic chromophores. 

Examples where group theory can be applied successfully are molecular orbital theory, molecular spectroscopy, multipole expansions, and ligand field theory. In general, group theoretical results can be used as classification scheme and/or to simplify numerical calculations. 

Actually, the recent studies of transition-group spectra have shown that two different models cherished by many theorists— the electrostatic ligand field model and the valency-bond description (more specifically, the Pauling hybridization theory)—cannot be applied to the observed distribution of energy levels. On the other hand, the molecular orbital (M.O.) configurations give an excellent classification of all energy levels of all complexes and a unified description is obtained of all polyatomic molecules. 

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