When a polydentate ligand simultaneously coordinates to a metal ion through more than one donor sites, a ring like structure is obtained which is known as chelate ring and the ligand is known as chelating ligand. Chelate complexes are more stable than ordinary complexes. The stability of complexes is greatly increased by the chelation. This is known as chelate effect.
eg. [Fe(EDTA)]– is more stable as it has five ring structure than [Cu(en)2]2+, it has two ring structure. Greater the number of rings present in a complex, greater is the stability of complex.
