This section will cover:
The bonding of transition metal complexes may be considered using two approaches, namely crystal field theory and molecular orbital theory. Molecular orbital theory takes a covalent approach, and considers the overlap of d-orbitals with orbitals on the ligands to form molecular orbitals; this is not covered on this site.
For more information on MO theory click here.
Crystal field theory takes the ionic approach and considers the ligands as point charges around a central metal positive ion, ignoring any covalent interactions. The negative charge on the ligands is repelled by electrons in the d-orbitals of the metal. The orientation of the d-orbitals with respect to the ligands around the central metal ion is important, and can be used to explain why the five d-orbitals are not degenerate. Whether the d-orbitals point along or in between the cartesian axes determines how the orbitals are split into groups of different energies. We shall examine the splitting of d-orbitals for octahedral, square planar and tetrahedral ligand geometries. But first let us look at the shapes and relative orientations of them.