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, spectrophotometrically and calorimetrically, in NaCl aqueous solution (0 < I ≤ 1 mol L− 1) and at t = 25 °C. The formation of two hydrolytic species VO(OH)+ and VO2(OH)22+ and one complex with sulfate was found, with log β = − 5.65 for the reaction VO2+ + H2O = VO(OH)+ + H+, log β = − 7.02 for the reaction 2VO2+ + 2H2O = (VO)2(OH)22+ + 2H+ and log K = 1.73 for VOSO40 species (at I = 0.1 mol L− 1 and t = 25 °C). For these species, using calorimetric data, ΔH and TΔS 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, λmax and εmax values for the relevant species in solution were determined.