Ligands are classified based on the number of donor atoms they use to attach to a central metal. Here’s a clear explanation:
1. Monodentate Ligands
- Definition: Ligands that have only one donor atom to form a bond with the metal.
- Example: Water (H₂O), ammonia (NH₃), chloride ion (Cl⁻)
- Key Point: Each monodentate ligand forms one coordinate bond with the metal.
2. Bidentate Ligands
- Definition: Ligands that have two donor atoms, allowing them to form two bonds with the same metal ion.
- Example: Ethylenediamine (en), oxalate ion (C₂O₄²⁻)
- Key Point: They can form a chelate ring with the metal, which increases stability.
3. Polydentate Ligands
- Definition: Ligands that have more than two donor atoms, allowing them to form multiple bonds with the metal ion.
- Example: EDTA (has six donor atoms), DTPA
- Key Point: These ligands can wrap around the metal, forming very stable chelates.
In short:
- Monodentate = 1 bond
- Bidentate = 2 bonds
- Polydentate = 3 or more bonds