Ligands

 

It is an ion or molecule capable of donating a pair of electrons to the central atom via a donor atom.
 

Types of Ligands

Unidentate ligands: Ligands with only one donor atom, e.g. NH₃, Cl^-, F^- etc.

Bidentate ligands: Ligands with two donor atoms, e.g. ethylenediamine, C₂O₄^2-(oxalate ion) etc. 

Tridentate ligands: Ligands which have three donor atoms per ligand, e.g. (dien) diethyl triamine.

Hexadentate ligands: Ligands which have six donor atoms per ligand, e.g. EDTA. 

Chelating Ligands: Multidentate ligand simultaneously co-ordinating to a metal ion through more than one site is called chelating ligand. These ligands produce a ring like structure called chelate. Chelation increases the stability of complex. This effect is called chelation effect.

Example:

                         _••                            _

          H₂C — NH₂           O = C — O :

            |       _••                   |       _

          H₂C — NH₂           O = C — O :

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