Chetan Mandayam Nayakar
Last Activity: 13 Years ago
Stronger is the metal-ligand bond, less is the dissociation in the solution and hence greater is the stability of a coordination compounds.
Instability constant for the complex ion [Cu(NH3)4]2+ i.e.
[Cu(NH3)4]2+ ? Cu2+ + 4NH3, is given by the expression; Ki = [Cu2+][NH3]4/[Cu(NH3)4]2+
Stability constant of the above complex i.e.
Cu2+ + 4NH3 ? [Cu(NH3)2+ is given as under ; K = [Cu(NH3)42+]/[Cu2+][NH3]4 = 1/K,
Greater is the stability constant, stronger is the metal – ligand bond
Factors affecting the stability of complex ion
(1) Nature of central metal ion : The higher the charge density on the central metal ion the greater is the stability of the complex
For example, the stability constant of [Fe(CN)6]3– is much greater than the stability constant of [Fe(CN)6]4–.
Fe2+ + 6CN– ? [Fe(CN)6]4–; K = 1.8 × 106
Fe3+ + 6CN– ? [Fe(CN)6]3–; K = 1.2 × 1031
Effective atomic number (EAN) or Sidgwick theory: In order to explain the stability of the complexes sidgwick proposed effective atomic number. EAN generally coincides with the atomic number of next noble gas in some cases. EAN is calculated by the following relation :
EAN = Atomic no. of the metal –e– lost in ion formation +No. of e– gained from the donor atom of the ligands.
EAN = Atomic number – Oxidation number + co-ordination no. × 2