Crystal Field Theory for Transition Metal Ions

4 CRYSTAL FIELD THEORY FOR TRANSITION METAL IONS 

Most of the transition metal oxides and salts may be treated as ionic crystals. The valence electrons of s symmetry (4s, 5s, or 6s) are stripped off. The metal forms an ion that is considerably smaller than the atom. The inner (n - l)d electrons (3d, 4d, or 5d) are degenerate in the central field approximation of the atom. In the next step, multiplets are formed (Section 2.4). In the third step, the transition metal ions interact with the crystal field, which is dominated by repulsion from the neighboring negative ions. This leads to a splitting of the 3d orbital energies. The theory describing the splitting of the electronic states in a crystal field is due to the American physicists Hans Bethe and John van Vleck and is called crystal field theory (CFT). 

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