Interaction of oxovanadium(IV) with carboxylic ligands in aqueous solution: A thermodynamic and visible spectrophotometric study

The hydrolysis of VO2+ and the complex with sulfate were studied potentiometrically, spectro photo metrically and calorimetrically, in NaCl aqueous solution (0 I <= 1 mol L-1) and at t=25 degrees C. The formation of two hydrolytic species VO(OH)(+) and VO2(OH)(2)(2+) and one complex with sulfate was found. with log beta=-5.65 for the reaction VO2+ +H2O = VO(OH)(+)+ H+, log beta=-7.02 for the reaction 2VO(2+) +2H(2)O=(VO)(2)(OH)(2)(2+) +2H(+) and log K= 1.73 for VOSO40 species (at I=0.1 mol L-1 and t=25 degrees C). For these species, using calorimetric data, Delta H and T Delta S values were also obtained. By using the above values, interactions of VO2+ with acetate (ac), malonate (mal), succinate (suc), 1,2.3-propanetricarboxylate (tca) and 1,2,3,4-butanetetracarboxylate (btc) ligands were studied potentiometrically and spectrophotometrically. The formation of ML+. ML20 and MLOH0 for ac: ML0, MLH+, ML22- and ML2H- for mal: ML0. MLH+ and MLOH- for suc; ML- and MLH0 for tca and ML2-, MLH- and MLH20 for btc were found. Formation constants are reported at I=0.1 mol L-1, together with SIT parameters for the dependence on ionic strength. By visible spectrophotometric measurements, lambda(max) and epsilon(max) values for the relevant species in solution were determined. (C) 2008 Elsevier B.V. All rights reserved.