Solution studies of systems with polynuclear complex formation. 1. The copper(II) citrate system

The complex formation between copper(II) and citrate ions (citric acid = H3L) has been investigated in the pH range of 4.5 to 10 by means of combined pH and pCu measurements. The emphasis was on the formation of the dimeric species and the concentration range chosen in the experiments favoured the formation of such species. The experimental data can be explained by the formation of the complexes Cu2H−1L, Cu2H−1L3−2, and Cu2H−2L4−2. The last complex is the predominating species even in very dilute neutral and weakly alkaline solutions containing an excess of ligand. A more highly polymeric fraction is observed in neutral solutions with an excess of metal ion.