Question

State the factors which govern stability of complexes.

Discuss the main factors which affect the stability of a complex in solution.

Answer 1

1. Charge on the central metal ion:
   • A complex’s stability is contingent upon the charge density of the central metal ion, which is in turn determined by the magnitude of charge and the radius of the ion, or the charge/radius ratio.
   • The charge density and stability of the complex increase with the charge’s magnitude and the ion’s size.
   • For example, Fe³⁺ forms more stable complexes than Fe²⁺ because of higher charge density.
2. Basic nature of the ligand:
   • Lewis bases are ligands that function as electron donors during the construction of a complex.
   • So, the stability of the complex depends on how easily the ligands can give away their lone pairs of electrons to the central metal ion.
   • Therefore, the stability of the complex is inversely proportional to the fundamental strength of the ligand.
3. Presence of chelate rings: Chelation increases the stability of complexes.