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

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 2 O = VO(OH) + + H + , log β = − 7.02 for the reaction 2VO 2+ + 2H 2 O = (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 T Δ 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 2 H − 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 e max values for the relevant species in solution were determined.