Question

Discuss the factors which affect the stability of a complex.

Answer 1

1. Charge density on the central metal ion: A complex’s stability is determined by the charge density on the central metal ion, which is determined by the magnitude of charge and the radius of the ion, also known as the charge/radius ratio. The bigger the magnitude of charge and the smaller the size of the ion, the greater the charge density and stability of the complex.
   For example, Fe³⁺ produces more stable compounds than Fe²⁺.
2. Nature of ligands: Ligands are Lewis bases because they donate electrons during complex formation. As a result, the stability of a complex should be determined by the ease with which the ligands donate lone pairs of electrons to the central metal ion, also known as the ligand’s basic strength. As a result, the higher the basic strength of the ligand, the more stable the combination. CN⁻ creates more stable complexes than H₂O.
   For example, CN⁻ is more basic than NH₃. As a result, cyanido complexes of a metal ion are more stable than ammine complexes, as evidenced by the data below:
   K for [Ag(CN)₂]⁻ = 5.5 × 10¹⁸
   K for [Ag(NH₃)₂]⁺ = 1.6 × 10⁷