DMPS

In chemistry, a ligand is either an atom, ion, or molecule that bonds to a central metal, generally involving formal donation of one or more of its electrons. The metal-ligand bonding ranges from covalent to more ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known involving Lewis acidic.

Ligands are classified in many ways: their charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). The size of a ligand is indicated by its cone angle.

Type of Ligand
i)Monodentate ligand

• are ligands which coordinates through only one atom. Some examples are H2O, NH3, P(CH3)3, etc.

ii)Polydentate ligand

• are ligands which coordinate through two or more donor atoms.
• also referred to as chelating ligands when the donor atoms are bonded to the same metal centre.
• Polydentate ligand can be divided into 3 :
  

1. Bidentate ligand

• have two lone pairs, both can bond to the central metal ion.
• examples are 1,2-diaminoethane
  

2. Tetradentate ligand

• Has four lone pairs, all of which can bond to the central metal ion.
• Examples are vitamin B-12.
• Vitamin B-12 is required in the diet of all higher animals which is only synthesized by certain bacteria and molds.

3. Hexadentate ligand

• Has six lone pairs of electrons - all of which can form coordinate bonds with the same metal ion.
• The best example is EDTA.