Why does crystal field theory fail to explain the relative strength of ligands? Justify with example.

Asked by ghoshputai | 19th Oct, 2010, 01:06: PM

Expert Answer:

Dear Student
Crystal field theory fails to explain the relative strength of ligands, since it considers that metal-ligand bond is purely electrostatic interaction between the metal and ligand. However this electrostatic interaction between metal and ligand fails to explain the relative position of ligands in the electrochemical series. The metal ligand bonding also has definitely partial covalent character alongwith electrostatic force, which also affects the ligand strength. The most obvious limit of this theory is that it can't explain three color of substances with a full or empty d orbital.(since it only consider d orbitals) An example of these substances is KMnO4 in which the d orbital is empty. there is another kind of electron transfer called Charge Transfer(CT) which is more powerful than d-d transfer and is between metal and ligand. this type of electron transfer is not covered in crystal field theory and can only be explained using MOT(molecular orbital theory)
We hope that clarifies your query.
With Best Regards,

Answered by  | 24th Oct, 2010, 06:58: PM

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