ABSTRACT
Metal ions can form complexes with solvent molecules and with ligands in solution. For the metal ions, it is important to combine with a preferred ligand which is able to impart higher stability. In the context of stability constant generally solvent molecules are water but non-aqueous solvents are preferred. The water molecules which surround the metal ions to form hydration spheres are not taken into account even in equilibrium constant. In general there are number of factors controlling stability of complexes. A complex comprises of a metal ion and a ligand therefore it is pertinent to discuss the kind of metal ions and ligands which together contribute to the stability. On the basis of energy consideration, if heat is evolved during the complexation then stability of complex is higher because the complex itself goes to the lower energy state. There are two factors on which stability of a complex depends: Type of metal ion, type of ligand.
