Coordination Compounds Ligands: an ion or molecule capable of donating a pair of electrons to the central atom via a donor atom. Unidentate ligands: Ligands with only one donor atom, e.g. NH 3 , Cl - , F - etc. Bidentate ligands: Ligands with two donor atoms, e.g. ethylenediamine, C 2 O 4 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 coordinating to a metal ion through more than one site is called chelating ligand. Example: Ethylenediamine (NH 2 CH 2 CH 2 NH 2 ) These ligands produce a ring like structure called chelate. Chelation increases the stability of complex. Werner’s Theory: Metals possess two types of valencies i.e. primary (ionizable) valency and secondary ...