Mixed-ligand complex formation in the system copper (II) – Salicylate ion-ethylenediamine

Mixed ligand complexation between Cu (II) ion, salicylate ion and ethylenediamine is studied potentiometrically using both a glass and a copper ion selective electrode at 25°C in a 0.1 mole dm-3 KNO3 medium. First protonation of salicylate ion is determined by continous spectrophotometric titration at 0.1 mole dm-3 and 1.0 mole dm-3, 25°C. Second protonation of salicylate and binary complexation of this ligand with Cu (II) ion is studied potentiometrically in the same conditions. Experimental data are analysed using MINIPOT and MINIQUAD programs. Stabilization of the mixed ligand complex, Cusalen (sal = salicylate ion, en = ethylenediamine), has been found higher than expected from statistical factors only. Small positive interactions between the two ligands in the ternary complex can be suspected