A scientist named Bethe proposed crystal field theory to explain the bonding nature in ionic crystals. Later on, this theory was applied by other scientists to account the magnetic properties of transition metal ions and their complexes. Crystal field theory received considerable support from the coordination chemists and hence it replaced the valence bond theory. Crystal field theory is based on the assumption that the interaction between the metal ions and the ligands is purely electrostatic in nature. When the ligands approach the central metal atom or ion, the five degenerate d-orbitals of the central atom become differential that is they split into different energy levels under the influence of the electrostatic field of ligands.
The Limitations Of Crystal Field Theory
The crystal field theory is highly useful and more significant as compared to the valence bond theory. Even after such useful properties, it has many limitations. The following points will clearly state the limitations of crystal field theory:
- The assumption that the interaction between metal-ligand is purely electrostatic cannot be said to be very realistic.
- This theory takes only d-orbitals of a central atom into account. The s and p orbits are not considered for the study.
- The theory fails to explain the behaviour of certain metals which cause large splitting while others show small splitting. For example, the theory has no explanation as to why H2O is a stronger ligand as compared to OH–.
- The theory rules out the possibility of having p bonding. This is a serious drawback because is found in many complexes.
- The theory gives no significance to the orbits of the ligands. Therefore it cannot explain any properties related to ligand orbitals and their interaction with metal orbitals.
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