Ligand Field Theory (LFT) helps explain the stability of metal complexes by showing how the interaction between metal d-orbitals and ligands affects energy and bonding. Here’s a explanation:
1. Ligand Field Stabilization Energy (LFSE)
- When ligands split the metal’s d-orbitals, electrons occupy the lower-energy orbitals.
- This lowers the overall energy of the complex.
- The energy gained is called Ligand Field Stabilization Energy (LFSE).
- Higher LFSE → more stable complex
2. Effect of Ligand Type
- Strong-field ligands (like CN⁻, CO) → larger d-orbital splitting → higher LFSE → more stable complexes.
- Weak-field ligands (like H₂O, Cl⁻) → smaller splitting → lower LFSE → less stable complexes.
3. Effect of Electron Configuration
- Metals with certain d-electron counts (like d³, low-spin d⁶) gain maximum LFSE, making complexes very stable.
- Example: [Fe(CN)₆]³⁻ (low-spin d⁵) is more stable than [Fe(H₂O)₆]³⁺ (high-spin d⁵).
4. Geometry and Bonding
- LFT explains why certain geometries (octahedral, square planar) are more stable for specific d-electron configurations.
- Covalent bonding and π-backbonding also contribute to stability.
In short
- LFT describes stability through d-orbital splitting, LFSE, ligand type, and electron configuration.
- More splitting and stronger bonding → higher stability