Complexation of uranyl with benzoic acid in aqueous solution at variable temperatures: potentiometry, spectrophotometry and DFT calculations

Investigation of the fundamental coordination chemistry between U(vi) and simple organic ligands is important to understand the chemical behavior of U(vi) in the natural environment and separation processes. In this work, the complexation of U(vi) with a common carboxylic acid, benzoic acid, has been systematically investigated through potentiometry, spectrometry and DFT calculations. Three successive complexes (UO2L+, UO2L2 and UO2L3-, L = benzoate ion) between U(vi) and benzoic acid are successfully identified in aqueous solution and their corresponding thermodynamic parameters (stability constant, enthalpy and entropy) are determined. Notably, this is the first time that the previously missing 1 : 2 and 1 : 3 (U to L) complexes in aqueous solution and their complexation thermodynamics have been reported, which would aid in more accurate prediction of the chemical behavior of U(vi) in the presence of benzoic acid. Moreover, the structures of the complexes are elucidated using DFT calculations, which show that benzoic acid coordinates to U(vi) in a bidentate form in all the complexes.