Question

How are ligands classified on the basis of the number of donor atoms? Give an example of each type.

Answer 1

Ligands classified on the basis of the number of donor atoms:

1. Unidentate ligands: Unidentate ligands or monodentate ligands are those that have only one donor atom and can establish a single coordinate bond with the central metal atom or ion.
   Example: NH₃, Cl⁻, H₂O
2. Didentate or bidentate ligands: Didentate ligands are defined as those that have two donor atoms and can make two coordinating bonds with the centre metal atom or ion.
   Example: \[\ce{C2O^2-_4}\](oxalate), en
3. Tridentate ligands: Tridentate ligands are those with three donor atoms and the ability to create three coordinate bonds with a central metal or ion.
   Example: Diethylenetriamine
4. Tetradentate ligands: The ligands which possess four donor atoms are called tetradentate ligands.
   Example: Triethylenetetramine (trien)
5. Pentadentate ligands: The ligands which contain five donor atoms are called pentadentate ligands. 
   Example: Ethylenediaminetriacetato
6. Hexadentate ligands: The ligands which contain six donor atoms are termed as hexadentate ligands.
   Example: Ethylenediaminetetraacetato (EDTA)
7. Bridging ligands: The monodentate ligands which can simultaneously attach themselves to more than one metal ion are called bridging ligands.
   Example: OH⁻, NH₂, NO₂, Cl⁻, CO.