Question

What is meant by stability of a coordination compound in solution? State the factors which govern stability of complexes.

Answer 1

The stability of coordination compounds in solution means the degree of association between the metal ion and the ligands involved in the state of equilibrium. Quantitatively, the stability is expressed by the equilibrium constant for the association.
$C{u}^{2+}\left(aq\right)+4N{H}_3\left(aq\right)\rightleftharpoons \left[Cu\right(N{H}_3{)}_4^{2+}\left]\right(aq)K=\frac{\left[Cu\right(N{H}_3{)}_4{]}^{2+}}{\left[C{u}^{2+}\right][N{H}_3{]}^4}$
Factors affecting the stability of a complex ion:
(a) The nature of the central metal atom
(1) Charge on the central metal ion
(2) Size of metal ion
(3) Electronegativity or charge distribution of metal ion
(4) Chelate effect
(5) Macrocylic effect
(b) The nature of the ligand
(1) Basic strength
(2) Size and charge of ligands