3.4—
Complexation Equilibria
The thermodynamic stability of a complex MLn formed from an acceptor metal ion M and ligand
groups L may be approached in two different but related ways. (The difference between the two
approaches lies in the way in which the formation reaction is presented.) Consistent with preceding
sections, an equilibrium constant may be written for the formation reaction. This is the formation
constant Kf. In a simple approach, the effects of the solvent and ionic charges may be ignored. A
stepwise representation of the reaction enables a series of stepwise formation constants to be written
(Table 3.5).
Table 3.5 Stepwise formation constants (mol–^1 dm^3 )Alternatively, a set of overall formation constants may be defined (Table 3.6).
Table 3.6 Overall formation constants (mol–n dm^3 n)The relations between values of Kf and values of β are simple and easily seen. For example, β 3 may be
multiplied by [ML]/[ML] and [ML 2 ]/[ML 2 ] to give
an expression which can be rearranged in the form