Valence Bond Theory

Linus Pauling of the California Institute of Technology developed the valance bond theory. Pauling’s ideas have had an important impact on all areas of Chemistry. He applied valence bond theory to coordination compounds. This theory can account reasonably well for the structure and magnetic properties of metal complexes.

The basic principles, which are involved in the valence bond treatment of coordination compounds are:

• (a) Hybridization of valance orbitals of the central metal or ion
• (b) Bonding between ligand and the metal ion or atom.
• (c) Relation between the type of bond and the observed magnetic behaviour.

Six Coordinate Complexes

Example: [CoF₆]^3-

The oxidation state of cobalt is +3. Cobalt atom has the outer electronic configuration 3d⁷4s². Thus, Co³⁺ ion will have the configuration 3d⁶. 

As Co³⁺ ion combines with six fluoride ligands in [CoF₆]^3–, empty atomic orbitals are required on the metal ion to receive the coordinated lone pair of electrons. The orbitals used are one 4s, three 4p and two 4d. These are hybridized to give a set of six equivalent sp³d² hybrid orbitals. A ligand orbital containing a lone pair of electron forms a coordinate bond by overlapping with an empty hybrid orbital on the metal ion. In this way a σ bond is formed with each ligand.