Coordination Compounds
9.0 Application of Crystal Field Splitting Theory (CFST)
9.0 Application of Crystal Field Splitting Theory (CFST)
1. We can determine the magnetic moment of the complex.
Example: ${\left[ {Fe{{(CN)}_6}} \right]^{ - 4}}$
Example: ${\left[ {Fe{{({H_2}O)}_6}} \right]^{ + 2}}$
2. It explains the color of the complexes.
Example: According to $VBT$ ${\left[ {Fe{{(CN)}_6}} \right]^{4 - }}$ has all paired electrons. Hence this should be colorless but it is an orange red colored substance which can be explained by CFST. In Ferrocyanide ion $d-d$ transitions are possible hence it is colored.
Limitations of crystal field theory
The crystal field model is successful in explaining the formation of structure, color and magnetic moment properties of coordination compounds to a large extent. However, from the assumption that the ligand is point charges, it follows the anionic ligands should exert the greatest splitting effect.
The anionic ligands actually are found at the low end of the spectrochemical series. Further, it does not take into account the covalent character of bonding between the ligand and central atom. These are some of the weakness of CFT, which are explained by the ligand field theory (LFT), and molecular orbital theory which are beyond the scope of the present study.
