Coordination compounds are the complex compounds in which the metal atoms are bound to a number of anions or neutral molecules.
The Valence Bond Theory (VBT) explains with reasonable success, the formation, magnetic behaviour and geometrical shapes of coordination compounds. It however fails to provide a quantitative interpretation of magnetic behaviour and has nothing to say about the optical properties of these compounds.
The Crystal Field Theory (CFT) to coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d orbital energies of the central metal atom/ion. The splitting of the d orbitals provides different electronic arrangements in strong and weak crystal fields. The treatment provides for quantitative estimations of orbital separation energies, magnetic moments and spectral and stability parameters.
The metal-carbon bond in metal carbonyls possesses both σ and π character. The ligand to metal is σ bond and metal to ligand is π bond. This unique synergic bonding provides stability to metal carbonyls.
The stability of coordination compounds is measured in terms of stepwise stability (or formation) constant or overall stability constant. The stabilization of coordination compounds due to chelation is called the Chelate effect. The stability of coordination compounds is related to Gibbs energy, enthalpy and entropy terms.
Applications of coordination compounds:
Provide insight into the functioning and structures of vital components of biological systems.