Splitting of d Orbital Energies in Octahedral Fields

When a metal ion is surrounded by anions in a crystal, there is an electrostatic field produced by the anions that alters the energies of the d orbitals of the metal ion. The field generated in this way is known as a crystal field. Crystal field theory was developed in 1929 by Hans Bethe in an attempt to explain the spectral characteristics of metal ions in crystals. It soon became obvious that anions surrounding a metal in a crystal gave a situation that is very similar to the ligands (many of which are 

We can convert this energy per molecule into kj mol-1 by the following conversion. 

Crystal field splitting energy compared to the electron pairing energy. 

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