For a mononuclear binary complex, if a central atom (central group) $\ce{M}$ (the 'metal') and a ligand $\ce{L}$ have been defined, then in the following expressions \(K_{n}\) is the stepwise formation constant, and \(\beta_{n}\) is the cumulative formation constant for the complex $\ce{ML_{n}}$. They can both be referred to as stability constants (stepwise and cumulative). \[K_{n}=K(\rm{ML}_{n- 1}+\rm{L}\rightleftharpoons \rm{ML}_{n})\] \[\beta_{n} = K(\rm{M}+n\rm{L}\rightleftharpoons \rm{ML}_{n})\]