Thermodynamic properties of actinide complexes. VII. Uranyl(VI)-succinate system

Luminescence studies of uranyl-aliphatic dicarboxylic acid complexes in acetonitrile medium

The uranyl (UO2 2+)-aliphatic dicarboxylic acid complexes are studied by luminescence and UV-Vis spectroscopy in acetonitrile (MeCN) medium. The ligands used are malonic acid (MA), succinic acid (SA), glutaric acid (GA), adipic acid (AA) and pimelic acid (PA). The complexes of UO2 2+ with the above ligands showed well resolved luminescence spectra at pH 4.0 with M/L = 5. Both luminescence and UV-Vis spectra indicated the formation of 1:2 and 1:3 complexes of UO2 2+ with MA and GA, AA, PA, respectively. DFT computations indicated the formation of 1:2 chelate complex of UO2 2+ with MA and two types of 1:3 complexes of UO2 2+ with SA, GA, AA and PA. Furthermore, the effect of solvent (water and acetonitrile) on the UO2 2+-ligand complexes has been performed using COSMO model. The present study demonstrates, for the first time, the formation of tris complexes of uranyl with these ligands in acetonitrile medium.

Complexation of An(vi) with succinic acid in aqueous acid solutions: uranyl vs. plutonyl

Due to stronger electrostatic interaction in a uranyl–succinate system, complex species of U(vi) with succinate are more stable than the ones of Pu(vi).

Thermodynamic study on the U(VI) complexation with dicarboxylates by calorimetry

The thermodynamic quantities (ΔG, ΔH and ΔS) of U(VI) complexation with oxalate, malonate, succinate, glutarate, adipate, phthalate, tartronate and malate, and of Eu(III) complexation with succinate, glutarate and adipate were determined by potentiometric and calorimetric titration techniques. The obtained thermodynamic quantities indicated that these complexation reactions are mainly driven by the entropy changes while the enthalpy changes are nearly zero or preventing the complexation. The thermodynamic quantities of 1:1 U(VI) complexes with 5 dicarboxylates having different carbon chain lengths (−OOC−(CH2) n −COO−) showed an interesting tendency, that is, −ΔH decreased and TΔS increased systematically with increasing the length of the carbon chain from n = 2 to 6. The comparison of TΔS values of 1:1 carboxylate formation with U(VI) and Eu(III) showed that TΔS of U(VI) were always lager than those of Eu(III). The entropies of 1:1 complex formation of U(VI) with hydroxycarboxylates were always smaller than those with carboxylates of the same carbon chain length, while the enthalpies of uranyl hydroxycarboxylates were always larger. This tendency was also observed in the protonation and the complex formation of Eu(III).

Dioxouranium(VI) – Carboxylate Complexes. Interaction with Dicarboxylic Acids in Alqueous Solution: Speciation and Structure

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.