Which of the following cannot be explained by crystal field theory?
- A.The order of spectrochemical series
- B.Magnetic properties of transition metal complexes
- C.Colour of metal complexes
- D.Stability of metal complexes
Show answer and solution
Correct option: A
Solution
Crystal Field Theory (CFT) treats ligands as pure point charges and considers only electrostatic interactions between the metal ion and ligands. It successfully explains magnetic properties (by predicting d-electron pairing based on Δ vs pairing energy), colour (via d-d transitions with energy equal to Δ), and stability (through crystal field stabilisation energy, CFSE).
However, the spectrochemical series — where certain ligands like CO and CN⁻ cause much larger splitting than expected from their charge or size — cannot be explained by CFT alone. These ligands are neutral or negatively charged yet produce very high Δ values due to π-backbonding, a covalent/orbital overlap concept that CFT completely ignores. Explaining the order of the spectrochemical series requires Ligand Field Theory or Molecular Orbital Theory, which account for covalent character and π-interactions between metal d-orbitals and ligand orbitals.
However, the spectrochemical series — where certain ligands like CO and CN⁻ cause much larger splitting than expected from their charge or size — cannot be explained by CFT alone. These ligands are neutral or negatively charged yet produce very high Δ values due to π-backbonding, a covalent/orbital overlap concept that CFT completely ignores. Explaining the order of the spectrochemical series requires Ligand Field Theory or Molecular Orbital Theory, which account for covalent character and π-interactions between metal d-orbitals and ligand orbitals.
[JEE Main 2023 · 24 Jan · Shift 2]