1314-64-3Relevant articles and documents
EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution
Hennig, Christoph,Schmeide, Katja,Brendler, Vinzenz,Moll, Henry,Tsushima, Satoru,Scheinost, Andreas C.
, p. 5882 - 5892 (2007)
The local structure of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution was investigated by U-L3 and Th-L3 EXAFS spectroscopy for total sulfate concentrations 0.05 ≤ [SO4 2-] ≤ 3 M and 1.0 ≤ pH ≤ 2.6. The sulfate coordination was derived from U-S and Th-S distances and coordination numbers. The spectroscopic results were combined with thermodynamic speciation and density functional theory (DFT) calculations. In equimolar [SO42-]/[UO 22+] solution, a U-S distance of 3.57 ± 0.02 A suggests monodentate coordination, in line with UO2-SO 4(aq) as the dominant species. With increasing [SO4 2-]/[UO22+] ratio, an additional U-S distance of 3.11 ± 0.02 A appears, suggesting bidentate coordination in line with the predominance of the UO2(SO4)22- species. The sulfate coordination of Th(IV) and U(IV) was investigated at [SO42-]/[M(IV)] ratios ≥8. The Th(IV) sulfato complex comprises both, monodentate and bidentate coordination, with Th-S distances of 3.81 ± 0.02 and 3.14 ± 0.02 A, respectively. A similar coordination is obtained for U(IV) sulfato complexes at pH 1 with monodentate and bidentate U-S distances of 3.67 ± 0.02 and 3.08 ± 0.02 A, respectively. By increasing the pH value to 2, a U(IV) sulfate precipitates. This precipitate shows only a U-S distance of 3.67 ± 0.02 A in line with a monodentate linkage between U(IV) and sulfate. Previous controversially discussed observations of either monodentate or bidentate sulfate coordination in aqueous solutions can now be explained by differences of the [SO42-]/[M] ratio. At low [SO4 2-]/[M] ratios, the monodentate coordination prevails, and bidentate coordination becomes important only at higher ratios.
Deactivation Mechanism of Excited Uranium(VI) Complexes in Aqueous Solutions
Park, Yoon-Yul,Sakai, Yoichi,Abe, Ryuji,Ishii, Takashi,Harada, Masayuki,et al.
, p. 55 - 60 (1990)
The rate of luminescence decay of various uranium(VI) complexes has been measured by a nitrogen laser photolysis method in aqueous solutions.It was found that the luminescence consisted of a short- and a longlived component in aqueous solutions at pH > 3.These components were assigned as the emissions from excited aqua and hydrolysed ions, *UO22+ and *(UO2)2(OH)22+, for which the decay constants were defined as k1 and k2, respectively. k1 and k2 were unaffected by either the concentration of UVI ion or the pH.The quenching rate constant, kq, of various UVI complexes (fluoro, sulphato, phosphato complexes as well as aqua ones) was determined in aqueous solutions with various anions, Cl-, Br-, I- and NCS-.The values of kq were well correlated with the redox potentials of quenching anions.The mechanism of the quenching reaction was interpreted on the basis of a linear free-energy relationship.
Formation of excited uranyl ion in oxidation of U(IV) with xenon trioxide in aqueous solutions of H2SO4 and HClO4: I. Influence of sulfate anions
Khamidullina,Lotnik,Kazakov
, p. 131 - 135 (2004)
Kinetic and chemiluminescent parameters of U(IV) oxidation with xenon trioxide in 1 M H2SO4 were studied in relation to complexation of U(IV) with SO42- anions. The rate constant of oxidation of the sulfate comp
Influence of temperature on the lifetime of electronically excited uranyl ion: I. Liquid and supercooled H2SO4 solutions
Lotnik,Khamidullina,Kazakov
, p. 550 - 554 (2003)
The influence of temperature (varied in the range 77-300 K) on the lifetime (τ) of electronically excited uranyl (UO22+)* in 0.2-5.0 M aqueous solutions of H2SO4 was studied. The activation parameters of the temperature quenching of the uranyl photoluminescence (PL) were determined. The temperature dependences of the rate constant of (UO22+)* PL decay (k = 1/τ) in 0.5 and 5 M H2SO4 obey the Arrhenius equation only at T > 265 K and T > 280 K, respectively. The deviations at low temperatures are probably due to both non-exponential temperature dependence of the viscosity of these solutions and a change in the chemical composition of the solvent (H 2SO4 dissociation), which affect the uranyl speciation and hence the luminescence parameters.
Stoichiometries and thermodynamic stabilities for aqueous sulfate complexes of U(VI)
Vercouter, Thomas,Vitorge, Pierre,Amekraz, Badia,Moulin, Christophe
, p. 2180 - 2189 (2009/01/31)
The formation constants of UO2SO4 (aq), UO 2(SO4)22-, and UO 2(SO4)34- were measured in aqueous solutions from 10 to 75°C by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A constant enthalpy of reaction approach was satisfactorily used to fit the thermodynamic parameters of stepwise complex formation reactions in a 0.1 M Na+ ionic medium: log10 K1(25°C) = 2.45 ± 0.05, ΔrH1 = 29.1 ± 4.0 kJ·mol-1, log10 K 2(25°C) = 1.03 ± 0.04, and ΔrH 2 = 16.6 ± 4.5 kJ·mol-1. While the enthalpy of the UO2(SO4)22- formation reaction is in good agreement with calorimetric data, that for UO 2SO4 (aq) is higher than other values by a few kilojoules per mole. Incomplete knowledge of the speciation may have led to an underestimation of ΔrH1 in previous calorimetric studies. In fact, one of the published calorimetric determinations of ΔrH1 is here supported by the TRLFS results only when reinterpreted with a more correct equilibrium constant value, which shifts the fitted ΔrH1 value up by 9 kJ·mol -1. UO2(SO4)34- was evidenced in a 3 M Na+ ionic medium: log10 K 3(25°C) = 0.76 ± 0.20 and ΔrH3 = 11 ± 8 kJ·mol-1 were obtained. The fluorescence features of the sulfate complexes were observed to depend on the ionic conditions. Changes in the coordination mode (mono- and bidentate) of the sulfate ligands may explain these observations, in line with recent structural data.
The effect of temperature on the quenching of the photoluminescence of the uranyl ion in liquid, supercooled, and solid aqueous solutions of sulfuric acid
Lotnik,Khamidullina,Kazakov
, p. 1170 - 1174 (2007/10/03)
The effect of temperature on the lifetime τ of electron-excited uranyl ions (UO22+)* in aqueous H2SO4 (0.2-5.0 M) solutions of UO2SO4 was studied over the temperature range from 77 to 300 K. The activation parameters for the temperature quenching of the photoluminescence (PL) of the electron-excited uranyl ion (UO22+)* were obtained. The temperature dependences of the (UO22+)* PL decay constant (k = 1/τ) obeys the Arrhenius equation only at T > 265 K for a 0.5 M H2SO4 solution and at T > 280 K for a 5 M H2SO4 solution. The temperature dependences of τ for the uranyl ion obtained while cooling the solutions from 300 to 77 K and during their heating exhibit extrema. DTA measurements show that the positions of these extrema coincide with the temperatures of the phase transitions in the samples. The effect of the phase transitions on the temperature dependence of τ is associated with not only the molecular mobility change caused by the phase transition (temperature quenching) but also the concentration quenching of (UO22+)*.
Dioxouranium (VI) Complexes of Benzoylhydrazine and Isonicotinoylhydrazine
Lal, R. A.
, p. 979 - 981 (2007/10/02)
Complexes of benzoylhydrazine (BH) and isonicotinoylhydrazine (IH) with uranyl sulphate and oxalate have been isolated and characterized on the basis of analytical, molar conductance, infrared and Raman spectral data.IR spectra indicate that BH and IH act as neutral bi- and tri-dentate ligands coordinating through C=O, -NH2 and C=O, -NH2 and pyridine nitrogen respectively.Sulphato and oxalato groups act as bridging and chelating bidentate ligands respectively.IR and Raman spectral data indicate that all ligand atoms are arranged in the equatorial plane around the UO2(2+) group which maintains its linearity in all the complexes.
