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

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The hydrolysis of VO 2+ 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 VO 2(OH) 2 2+ and one complex with sulfate was found, with log β = − 5.65 for the reaction VO 2+ + H 2O = VO(OH) + + H +, log β = − 7.02 for the reaction 2VO 2+ + 2H 2O = (VO) 2(OH) 2 2+ + 2H + and log K = 1.73 for VOSO 4 0 species (at I = 0.1 mol L − 1 and t = 25 °C). For these species, using calorimetric data, Δ H and TΔ S values were also obtained. By using the above values, interactions of VO 2+ 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 +, ML 2 0 and MLOH 0 for ac; ML 0, MLH +, ML 2 2− and ML 2H − for mal; ML 0, MLH + and MLOH − for suc; ML − and MLH 0 for tca and ML 2−, MLH − and MLH 2 0 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, λ max and ε max values for the relevant species in solution were determined.