In Ligand Field Theory (LFT), back-bonding (or π-backbonding) is when electrons flow from the metal to the ligand, and it has important effects on the metal-ligand bonding and properties of the complex. Here’s a explanation:
1. What is Back-Bonding?
- Occurs when the metal donates electrons from its d-orbitals into empty π orbitals* of the ligand.
- Common with ligands like CO, CN⁻, NO⁺.
2. Effects on the Complex
- Stabilizes the complex
- The extra bonding between metal and ligand makes the complex stronger.
- Increases d-orbital splitting
- Electrons in metal d-orbitals interact with ligand orbitals, increasing the ligand field strength.
- Changes electron density
- Metal loses some electron density to the ligand.
- Ligand gains electron density, which can affect reactivity.
- Influences properties
- Color: Larger splitting may change the wavelength of light absorbed.
- Magnetism: Can favor low-spin complexes.
- Reactivity: Activated ligands are more reactive in catalytic processes.
In short
- Back-bonding strengthens the bond, increases splitting, and affects color, magnetism, and reactivity.
- It’s a key reason why some ligands (like CO) form very stable complexes.