Quantification of Intramolecular Ligand Equilibria in Metal-Ion Complexes

That in a metal-ion chelate one binding site may be more weakly bound than another is often expected, though it is not equally well realized that such differences in metal-ion affinities may give rise to intramolecular equilibria between open and closed, i.e. chelated, forms. Quantification procedures for such equilibria are outlined and applied to describe the situation in complexes of N-substituted iminodiacetate and α-substituted acetate ligands. Corresponding procedures are applicable to the characterization of intramolecular ligand-ligand interactions in mixed ligand complexes. Isomerization equilibria are of general importance; e.g. in metal-ion catalyzed or facilitated technical or biological processes.