pH-Metric equilibrium invest&ations were carried tions are to be found in the more recent complex out to determine the stability constants of sixteen chemical literature [l-7, 91. It may be stated from copper(II)-diamine-glycine or copper(II)-diaminethese that, besides the statistical factor, other condiamine mixed ligand complexes. The corresponding stituents of fundamental importance in determining enthalpy values were obtained in calorimetric the stability are the steric, electrostatic and strucmeasurements.
tural factors.
In every system studied, an increased stability was observed compared to the statistical case. It was found that, for a given 'B" ligand, the formation of the mrjced ligand complexes is the more favoured, the greater the difference between the logK,JK2 values of the parent complexes. The stability increase was explained by the larger enthalpy change in the copper(II)+iamine-diamine complexes, and by the combined effect of the enthalpy and entropy changes in the copper(II)-diamine-glycine systems.
Up to the present there have been relatively few publications dealing with thermodynamic studies on mixed ligand complexes [12, 141. However, it is important to carry out calorimetric measurements, as thermodynamic data differing from their statistical values may certainly originate from special effects arising in the course of mixed ligand complex formation.