formation constant

For a mononuclear binary complex, if a central atom (central group) M (the 'metal') and a ligand L have been defined, then in the following expressions $K n$ is the stepwise formation constant, and $β n$ is the cumulative formation constant for the complex ML_n. They can both be referred to as stability constants (stepwise and cumulative).

$K n = K ( ML n − 1 + L ⇌ ML n )$