Thermodynamic Study on the Dissociation and Complexation of Coumarinic Acid with Neodymium(III) and Dioxouranium(VI) in Aqueous Media

In the frame of a systematic study on sequestering ability natural antioxidants towards metal cations, complexation coumarin-3-carboxilic acid (HCCA) with neodymium(III) and dioxouranium(VI) (uranyl, UO22+), overall stability constants resulting complexes, were evaluated from pH-potentiometric titration data at 37 °C in an aqueous solution (i.e., 0.16 mol/L NaClO4). The graphic representation complex’s concentration curves is given by distribution diagrams, which provide depiction all species present selected pH ranges. protonation constant HCCA was also determined to evaluate competition ligand for cations H+. ligand-to-metal ratio varied between 1 10, hydrogen ion decreased stepwise until incipient precipitation basic salt metal, occurred different values depending specific cation ratio. Speciation profiles obtained potentiometric titrations supported UV-Vis show that occurs ligand-to-Nd(III) –UO22+ 1:1 2:1, degrees deprotonation: Nd(OH)(CCA)+, UO2(OH)(CCA), UO2(OH)2(CCA)−, Nd(OH)(CCA)2, UO2(CCA)2 (UO2)2(OH)2(CCA)2.