The Formation Constant ($K_f$ or ${\beta }_n$) represents the equilibrium of complex formation: $M+nL\rightleftharpoons [M{L}_n],K_f=\frac{[M{L}_n]}{[M][L{]}^n}$

• A large value of $K_f$ means that at equilibrium, the concentration of the complex is much higher than that of free metal ions and ligands.
• This signifies a highly stable complex. Conversely, $K_d$ (dissociation constant) is $1/K_f$; a low dissociation constant indicates high stability.