Arturo Bismondo

Complexation of uranium(VI) with malonate at variable temperatures

Summary The complexation between uranium(VI) and malonate in 1.05 mol kg−1 NaClO4 was studied at variable temperatures (25, 35, 45, 55 and 70 °C). The formation constants of three successive complexes, UO2(OOCCH2COO), UO2(OOCCH2COO)22− and UO2(OOCCH2COO)34−, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. The heat capacity of the complexation, Δ Cop,m(MLj), is calculated to be 96 ± 12, 195 ± 15 and 267 ± 22 J K−1 mol−1 for j=1, 2 and 3, respectively. Extended X-ray Absorption Fine Structure Spectroscopy helped to characterize the coordination modes in the complexes in solution. UV/Vis absorption and luminescence spectra at different temperatures provided qualitative information on the temperature effect. The effect of temperature on the complexation between uranium(VI) and malonate is discussed in terms of the electrostatic model and compared with the complexation between uranium(VI) and acetate.

Thermodynamic Studies of the Complexation between Neodymium and Acetate at Elevated Temperatures

Complexation of neodymium (III) with acetate in 2.2 mol-kg-1 NaClO4 solution was studied at elevated temperatures (45 and 70°C) by potentiometry, calorimetry, and optical spectroscopy. The formation constants of the consecutive complexes, Nd(OOCCH3),2+ Nd(OOCCH3)2+, and Nd(OOCCH3)3, and the molar enthalpies of complexation at these temperatures were determined. The stability of the three complexes increases with increased temperatures, because of increased positive entropy change at higher temperatures, which exceeds the increased values of the positive (endothermic) enthalpy. The molar heat capacity changes of complexation ΔCp,m(MLj) (J-K-1-mol-1) for Nd(OOCCH3)j(3-j)+ in the temperature range from 25 to 70°C were calculated to be: 102 ± 13 (j = 1); 122 ± 19 (j = 2); and 239 ± 27 (j = 3). The effect of temperature on the complexation is discussed in terms of the electrostatic model.

Complexation of uranium(VI) with acetate at variable temperatures

The complexation between uranium(VI) and acetate in 1.05 mol kg−1 NaClO4 was studied at variable temperatures (25, 35, 45, 55 and 70 °C). The formation constants of three successive complexes, UO2(OOCCH3)+, UO2(OOCCH3)2 and UO2(OOCCH3)3−, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) provided structural information to identify the coordination modes of the acetate in the complexes in solution, which helped to interpret the trends in the enthalpy and entropy of the complexation. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.

Thermodynamic properties of actinide complexes. Part. III. Uranyl(VI)-glycolate system

Abstract The changes in free energy, enthalpy and entropy for the formation of uranyl(VI)-glycolate complexes, have been determined at 25 °C and in aqueous perchlorate medium 1.00 M. All three complexes formed, are found to be stabilized by entropy, while the enthalpy term, excepting the third step, opposes the complex formation. The data are in agreement with the presence of chelate structures in a decreasing measure for each of the three successive steps of complexation.

Calorimetric and spectroscopic studies of Eu(III) complexation with tetramethylmalonamide and tetramethylsuccinamide in acetonitrile and dimethylsulfoxide

Abstract The complexation of Eu(III) with two N , N , N′ , N′ -alkyl-substituted diamide ligands, tetramethylmalonamide (TMMA) and tetramethylsuccinamide (TMSA), was studied in organic solvents using titration calorimetry, FT IR and luminescence spectroscopy. The formation constants and enthalpy changes of the complexation were determined in pure acetonitrile and in acetonitrile containing small amounts of dimethyl sulfoxide (DMSO). It was observed that TMMA forms stronger complexes with Eu(III) than TMSA in the latter systems, which is attributed to the structural difference between TMMA and TMSA and an entropy effect. The effect of Eu(III) solvation by DMSO on the formation of the Eu(III)–diamide complexes is also discussed.

Complexation of thorium(IV) by tris((2,3-dihydroxybenzylamino)ethyl)amine—a new strong chelating agent

Abstract The interaction of thorium(IV) with tris((2,3-dihydroxybenzylamino)ethyl)amine (TRENCAT) has been investigated by means of potentiometric measurements in an aqueous solution of 0.1 mol dm −3 sodium perchlorate at 25°C. The formation of a chelate structure, as well as of protonated compounds has been observed. The values of the formation constants of these complexes are reported.

Interaction of thorium(IV) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.

Thermodynamics of the complex formation between uranyl(VI) and some polypeptides in aqueous solution

Abstract Potentiometric and calorimetric investigations of uranyl(VI) complexes with glycylglycine and glutathione have been carried out in 1.0 mol dm −3 aqueous solution of sodium perchlorate at 25.0 ° C. The experimental data of the urany(VI)-glycylglycine system can be explained by assuming the formation of three successive entropy-stabilized mononuclear complexes, whereas for the uranyl(VI)-glutathione system, a 1:1 complex only is present, due to the low pH values at which precipitation of solid compounds occurs. The values obtained for the stability constants and for the enthalpy and entropy changes are discussed in comparison with parent complexes involving some amino acid ligands.

Complexation of thorium(IV) with acetate at variable temperatures

The complexation between Th(IV) and acetate in 1.05 mol kg(-1) NaClO4 was studied at variable temperatures (10, 25, 40, 55 and 70 degrees C). The formation constants of five successive complexes, Th(Ac)j(4-j)+ where Ac = CH3COO- and j = 1-5, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray absorption fine structure spectroscopy (EXAFS) provided additional information on the complexes in solution. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.

INTERACTION OF NEPTUNIUM(V) WITH DICARBOXYLATE LIGANDS.

present work is done on the extraction of other elements by these solvents from media, which showed good extraction of antimony, and on the application of this extraction for radiochemical separation and activation analysis of antimony. Procedures for the separation of the two oxidation species of antimony, directly from sulphuric acid solutions will be valuable in studying the effect of the various factors (e.g. time, temperature, y-radiation) on the transformation of one oxidation state to the other in such solution. This may also be valuable for using antimony sulphate in radiation dosimetry.