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 a complex in a solution refers to the degree of association between the two species involved in a state of equilibrium. Stability can be expressed quantitatively in terms of stability constant or formation constant.
\(M+3L↔ML_3\)
Stability constant\(,β=\frac{[ML_3]}{[M][L]^3}\)
For this reaction, the greater the value of the stability constant, the greater is the proportion of \(ML_3\) in the solution. Stability can be of two types:
(a) Thermodynamic stability: The extent to which the complex will be formed or will be transformed into another species at the point of equilibrium is determined by thermodynamic stability. 
(b) Kinetic stability: This helps in determining the speed with which the transformation will occur to attain the state of equilibrium. 
Factors that affect the stability of a complex are: 
(a) Charge on the central metal ion: The greater the charge on the central metal ion, the greater is the stability of the complex. 
2. Basic nature of the ligand: A more basic ligand will form a more stable complex. 
2. Presence of chelate rings: Chelation increases the stability of complexes.