12.0 Stability of Co-ordination compounds

  Coordination Compounds

• The stability of the complex in solution refer to the degree of association between the two species involved in the state of equilibrium. The magnitude of the (stability or formation) equilibrium constant for the association, quantitatively expresses the stability. The stability of the complex is expressed in the terms of stability constant ($k$). If $k$ is more stability is more.$$\begin{equation} \begin{aligned} M + nL \to MLn \\ M + L \to ML{\text{ = }}{{\text{k}}_1} = \frac{{\left[ {ML} \right]}}{{\left[ M \right]\left[ L \right]}} \\ ML + L \to M{L_2}{\text{ = }}{{\text{k}}_2} = \frac{{\left[ {M{L_2}} \right]}}{{\left[ {ML} \right]\left[ L \right]}} \\\end{aligned} \end{equation} $$$$\begin{equation} \begin{aligned} M{L_{n - 1}} + L \to M{L_n} = {k_n} = \frac{{\left[ {M{L_n}} \right]}}{{\left[ {M{L_{n - 1}}} \right]\left[ L \right]}} \\ M + nL \to M{L_n} \to k = {k_1} \times {k_2} \times {k_3} \times {k_4} - - - - - - - \times {k_n} \\ k = \frac{{\left[ {M{L_n}} \right]}}{{\left[ M \right]{{\left[ L \right]}^n}}} \\\end{aligned} \end{equation} $$

• $\frac{1}{k}$ is called instability constant.