Study of coordination equilibria in systems of coexisting mononuclear and polynuclear complexes by an isosbestic point-spectrophotometric method.

This paper reports a method for determining the stability constants of complexes in a system of coexisting mononuclear and polynuclear complexes based on analysis of dual isosbestic points. First it is necessary to determine the dissociation degrees of either of the two complexes concerned in two directions, and then their stability constants. With this method, the conditional constant can be evaluated by appropriate treatment and selection of the proper equations for solutions. For demonstration purposes the scandium/Xylenol Orange system was used to test the model and satisfactory results were obtained.