A REINVESTIGATION OF THE THERMODYNAMICS OF FORMATION OF COMPLEXES OF NICKEL(II) WITH 2,2'-OXYBISETNANAMINE AND 2(2-AMINOETHYL) AMINOETHANOL

The thermodynamics of complexation of the ligands 2,2'-oxybisethanamin e (oden) and 2-(2-aminoethyl)aminoethanol (etolen) with the Ni2+ ion w ere re-investigated by glass electrode potentiometry and titration cal orimetry at 25 degrees C and in 0.5 mol dm(-3) KNO3. In the case of th e ligand etolen the data were consistent with previously reported comp lexes, Ni(etolen)(2+) and Ni(etolen)(2)(2+), and associated stability constants, However, the enthalpies of complexation obtained here diffe r from those previously reported. Reasons for these discrepancies are discussed. For the ligand oden the data could only be explained by the inclusion of the ternary species Ni(oden)OH+ and Ni(oden)(2)OH+ in ad dition to the binary species Ni(oden)(2+) and Ni(oden)(2)(2+). Thermod ynamic parameters of complexation for these complexes are reported and compared with those of the etolen complexes.