In Ligand Field Theory (LFT), covalent bonding plays a key role in explaining the real nature of metal-ligand interactions, which Crystal Field Theory (CFT) cannot. Here’s a explanation:
1. Beyond Electrostatics
- CFT treats ligands as point charges and considers only ionic (electrostatic) interactions.
- LFT adds covalent character, showing that metal and ligand orbitals overlap to share electrons.
2. σ-Bonding
- Ligand lone pairs overlap with empty metal orbitals to form σ bonds.
- This strengthens the bond and influences d-orbital splitting.
3. π-Bonding / π-Backbonding
- Some ligands (like CO or CN⁻) can accept electron density from the metal (π-backbonding) or donate via π orbitals.
- This modifies the electronic structure of the complex and increases stability.
4. Effect on Properties
- Covalent bonding affects:
- d-orbital splitting (ligand field strength)
- Color of the complex
- Magnetism (spin state)
- Reactivity of the complex
In short
- Covalent bonding in LFT explains why metal-ligand bonds are partially covalent, not purely ionic.
- It makes the theory more realistic than CFT and helps predict stability, reactivity, and electronic properties of complexes.