Crystal Field Theory was given by Hans Bethe and Van Vleck. This theory is based on the assumption that the interaction between metal ion and ligands is purely electrostatic in nature. When the ligands approach the central metal atom or ion, the five degenerate d-orbital of the central atom become different i.e.they split into the different energy level under the influence of the electrostatic field of ligands.
Limitations of Crystal Field Theory:
Crystal field theory explains successfully the structure of complex, magnetic properties, color, and electronic spectra, thermodynamic and kinetic aspects of the complexes. However, this theory has some serious limitations.
- In CFT only d-electrons of the metal ion are considered, the other orbitals such as s, are not taken into consideration.
- This theory has not considered the covalent character in transition metal complexes. It treats the metal-ligand as purely ionic.
- CFT cannot explain the relative strength of ligands as given in spectrochemical series, i.e. it cannot explain why H2O is a stronger ligand as compared to OH- ion.
- CFT has also not considered the Pi bonding in complexes either it is metal to ligand or ligand to metal.
- This theory has no significance to the orbits of the ligands. Therefore it cannot explain any properties related to ligand orbitals and their interaction with metal orbitals.
- It don't explain the effect of π bond on Δ.
- The compounds like in which metal is in zero oxidation states and the ligand is neutral have no electrostatic attraction between the metal and the ligands.