Any atom, ion or molecule which is capable of donating a pair of electrons to the central metal atom is called a ligand (or a coordinating group).

In a ligand, the particular atom which actually donates the electron pair is called the donor atom. Ligands may contain one or more than one donor atoms for coordination to the central metal ion. Accordingly the ligands are classified as:

Monodentate or unidentate ligands :

If a ligand contains only one donor atom, i.e., it is capable of forming only one coordinate bond to the metal atom, such a ligand is classified as a monodentate or unidentate ligand.

Some common unidentate ligands that are generally found in transition metal complexes are listed below:

  SOME COMMON UNIDENTATE LIGANDS

Bidentate ligands have two donor atoms present in a molecule. They have the ability to coordinate to the central metal ion through both the atoms, thus simultaneously forming two coordinate bonds. Some very common examples of bidentate ligands are:


Multidentate or polydentate Ligands:

If a ligand contains more than two donor atoms which can simultaneously coordinate to the central metal ion. the ligand is referred to as multi or  potentate ligand.

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