Stability constants of uranium(VI) and thorium(IV) complexes formed with 8-hydroxyquinoline and its 5-sulfonic acid derivative

In this study, the stability constants of uranium(VI) and thorium(IV) complexes formed with 8-hydroxyquinoline (8-HOQ) and its 5-sulfonic acid (8-HOQ-5-SO₃H) derivative have been determined using the Irving-Rossotti method, computing the Calvin-Bjerrum pH-titration data. As a result, it is determined that the thorium(IV) complexes are considerably more stable than the corresponding uranium(VI) complexes. On the other hand, the complexes formed between 8-HOQ-5-SO₃H and uranium(VI) or thorium(IV) are less stable than the corresponding 8-HOQ complexes.     

Stability constants and spectroscopic properties of thorium(IV)-arsenazo III complexes in perchloric acid

The complexation of thorium with arsenazo III in perchloric acid was quantitatively investigated with ultraviolet–visible (UV–Vis) absorption spectroscopy. The UV–Vis absorption of both 1:1 and 1:2 (thorium to arsenazo III) complexes in perchloric acid were found to be highly enhanced than the previously reported absorption of the complexes in hydrochloric acid. The stability constants of thorium-arsenazo III complexes were determined via computational analysis, and the SIT (specific ion interaction theory) was employed to evaluate the dependence on ionic strength. This work contributes to a better understanding of the speciation and spectroscopic properties of thorium-arsenazo III complexes at high ionic strength.

     

Preparation and characterizations of new U(IV) and U(VI) complexes with carboxylate ligands

The synthesis and characterization of some uranyl(VI) complexes containing glycolate (gly = CH₂OHCOO⁻) and methoxyacetate (MeOAc = CH₃OCH₂COO⁻) ligands with metal:ligand ratios of 1:1 and 1:2 are reported. In addition, new stable uranium(IV) complexes containing the same ligands, or the oxydiacetate (oda = ⁻OOCCH₂OCH₂COO⁻) anion, have been prepared by photolysing aqueous solutions of uranyl(VI) nitrate in the presence of an excess of ligand. The possible structures of these complexes are discussed on the basis of IR results. The photoproduction mechanism of U(IV) complexes is proposed from electronic and spectrofluorimetric spectra and quantum yield data.     

EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution

The local structure of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution was investigated by U-L(3) and Th-L(3) EXAFS spectroscopy for total sulfate concentrations 0.05 < or = [SO(4)(2-)] < or = 3 M and 1.0 < or = pH < or = 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 [SO(4)(2-)]/[UO(2)(2+)] solution, a U-S distance of 3.57 +/- 0.02 Angstrom suggests monodentate coordination, in line with UO(2)SO(4)(aq) as the dominant species. With increasing [SO(4)(2-)]/[UO(2)(2+)] ratio, an additional U-S distance of 3.11 +/- 0.02 Angstrom appears, suggesting bidentate coordination in line with the predominance of the UO(2)(SO(4))(2)(2-) species. The sulfate coordination of Th(IV) and U(IV) was investigated at [SO(4)(2-)]/[M(IV)] ratios > or = 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 Angstrom, 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 Angstrom, 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 Angstrom 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 [SO(4)(2-)]/[M] ratio. At low [SO(4)(2-)]/[M] ratios, the monodentate coordination prevails, and bidentate coordination becomes important only at higher ratios.     

Equilibrium constants of U(VI)-tri-isooctylammonium acetate complexes in various organic diluents

The extraction of U(VI) from acetic acid by solutions of tri-isooctylammonium acetate in carbon tetrachloride, benzene and xylene has been studied. The equilibrium constants for the acetate salt of tri-isooctylamine, R₃NHCH₃COO, in carbon tetrachloride is reported.Extraction of microconcentrations of U(VI) by solutions in benzene and xylene of tri-isooctylammonium acetate and of macroconcentrations of U(VI) by solutions in carbon tetrachloride has indicated the overall formula for the complex of this salt with uranyl acetate [(R₃NHCH₃COO)₂UO₂(CH₃COO)₂]. The equilibrium constants in the three diluents for the complex [(R₃NHCH₃COO)₂UO₂(CH₃COO)₂] are reported.Spectra taken in benzene and carbon tetrachloride solutions confirm that the same compound exists in both diluents.     

Potentiometric studies on aqueous fluoride complexes of actinides: Stability constants of Th(IV)-, U(IV)-, Np(IV)- and Pu(IV)-fluorides

The extraction behaviour of Th(IV) and U(VI) in extraction chromatography has been investigated on the basis of partition and infrared studies. The stationary phase was purified undiluted TBP supported on Amberlite XAD-4 and the mobile phase was nitric acid. The results have shown that the equilibria for the extraction of Th(IV) and U(VI) by the TBP/XAD-4 resin agreed very closely with those in solvent extraction.     

Determination of the equilibrium formation constants of two U(VI)-peroxide complexes at alkaline pH

The formation of uranyl-peroxide complexes was studied at alkaline media by using UV-Visible spectrophotometry and the STAR code. Two different complexes were found at a H(2)O(2)/U(VI) ratio lower than 2. A graphical method was used in order to obtain the formation constants of such complexes and the STAR program was used to refine the formation constants values because of its capacity to treat multiwavelength absorbance data and refining equilibrium constants. The values obtained for the two complexes identified were: UO(2)(2+) + H(2)O(2) + 4OH(-) UO(2)(O(2))(OH)(2)(2-) + 2H(2)O: log β°(1,1,4) = 28.1 ± 0.1 (1). UO(2)(2+) + 2H(2)O(2) + 6OH(-) UO(2)(O(2))(2)(OH)(2)(4-) + 4H(2)O: log β°(1,2,6) = 36.8 ± 0.2 (2). At hydrogen peroxide concentrations higher than 10(-5) mol dm(-3), and in the absence of carbonate, the UO(2)(O(2))(2)(OH)(2)(4-) complex is predominant in solution, indicating the significant peroxide affinity of peroxide ions for uranium and the strong complexes of uranium(VI) with peroxide.     

Stability constants of manganese(II) bromide complexes

Manganese-54 has been used as a tracer in an investigation of solutions containing manganese(II) bromide complexes. By a cation-exchange method values have been obtained for the stability constants beta(j) = [MnBr((2-j)+)(j)]/[Mn(2+)][Br(-)](j), valid for 20 degrees and ionic strength 0.691M maintained with perchloric acid.     

Stability constants of iron(III) borate complexes

The ultraviolet absorbance data from experiments conducted at constant pH and total iron concentration but variable B(OH)₃ concentration were used to determined the stability constants of FeB(OH) ₄ ²⁺ and Fe[B(OH)_{4 2} ⁺ at 25°C and an ionic strength of 0.68. The estimates obtained were *₁ = 1.0 ± 0.2 × 10^–2 and *₂ = 2 ± 1 × 10^–5, respectively (uncertainties are two times the standard error of the estimates). A calculation of the extent of iron(III) borate formation in ocean water at pH 8.2 shows that iron(III) borates are not a significantly large component of iron(III) speciation in seawater.     

Stability constants of lanthanide complexes with salicylhydroxamic acid

The stability constants of La, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb and Y complexes of salicylhydroxamic acid have been determined potentiometrically in 3:1 v v acetone-water medium at 25 +/- 0.5 degrees and at an ionic strength of 0.1 with respect to sodium perchlorate. The stability constants are comparable with those of other lanthanide complexes with oxygen-donating ligands such as benzoylacetone and benzoylphenylhydroxylamine.     

Stability constants of iron(II) sulfate complexes

The complex formation equilibria between iron(II) and sulfate ions have been studied at 25 degrees C in 3 M NaClO4 ionic medium by measuring with a glass electrode the competition of Fe2+ and H+ ions for the sulfate ion. The concentrations of the metal and of the ligand were varied in the ranges 0.01 to 0.125 and 0.01 to 0.250 M, respectively. The analytical concentration of strong acid was chosen to be 0.01 or 0.03 M. The potentials of the glass electrode, corrected for the effect of replacement of medium ions with reagent species, have been interpreted with the equilibria [formula: see text] Stability constants valid in the infinite dilution reference state, logK zero = 1.98 +/- 0.16, log beta 1 zero = 2.1(5) +/- 0.2 and log beta 2 = 2.5 +/- 0.2, have been estimated by assuming the validity of the specific interaction theory.     

Formation constants of ternary complexes of vanadium(IV) with picolinic acid and salicylic or 5-sulphosalicylic acid

The formation constants, beta(MAL), for the reaction VO(2+) + A(-) + L(2-) <==> VOAL(-) [where HA = picolinic acid and H(2)L = salicylic or 5-sulphosalicylic acid] have been determined at 30 +/- 1 degrees (mu = 0.1, KNO(3)). Potentiometric evidence is presented for the simultaneous addition of both ligands to the metal ion to form the 1:1:1 ternary complex.     

Stability of plutonium(IV) and plutonium(VI) in nitric acid solutions under strong α-irradiation

Plutonium(IV) oxidation has been studied in 1 to 20 mol/1 HNO₃ under 1 to 14 W/1 internal alpha-irradiation and at plutonium concentrations from 2 to 100 mmol/1. Curium isotopes have been used as the basic alpha-irradiation sources. It has been established that in the systems investigated both oxidation of plutonium(IV) and reduction of plutonium(VI) take place, resulting with time in reaching the equilibrium between plutonium(IV) and plutonium(VI). The presence of plutonium(IV) enhances the reduction of plutonium(VI). The rate constants for plutonium(IV) oxidation and plutonium(VI) reduction have been estimated and their dependences upon the concentrations of nitric acid, plutonium(IV) and plutonium(VI) as well as upon the dose rate investigated. An equation has been derived which permits to calculate the concentrations of plutonium(IV) and plutonium(VI) at any desired time.     

Pi-acid/pi-base carbonyloxomolybdenum(IV) complexes and their oxomolybdenum(VI/IV) precursors

Brown TpiPrMoO(SR)(CO) (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; R = Et, iPr, Ph, p-tol, Bz) are formed when TpiPrMoO(SR)(NCMe) react with CO gas in toluene. The carbonyloxomolybdenum(IV) complexes exhibit nu(CO) and nu(Mo=O) IR bands at ca. 2025 and 935 cm(-1), respectively, and NMR spectra indicative of C(1) symmetry, with delta(C)(CO) ca. 250. The crystal structure of TpiPrMoO(SiPr)(CO), the first for a mononuclear carbonyloxomolybdenum complex, revealed a distorted octahedral geometry, with d(Mo=O) = 1.683(3) A, d(Mo-C) = 2.043(5) A, and angle(O=Mo-C) = 90.87(16) degrees . The blue-green acetonitrile precursors are generated by reacting cis-TpiPrMoO2(SR) with PPh3; they are unstable, display a single nu(Mo=O) IR band at ca. 950 cm(-1), and exhibit NMR spectra consistent with C1 symmetry. Red-brown cis-TpiPrMoO2(SR) (R = as above and tBu) are formed by metathesis of TpiPrMoO2Cl and HSR/NEt3 in dichloromethane. The complexes exhibit strong nu(MoO2) IR bands at ca. 925 and 895 cm(-1), and NMR spectra indicative of Cs symmetry; the isopropyl, p-tolyl, and benzyl derivatives possess distorted octahedral geometries, with d(Mo=O)(av) = 1.698 A and angle(MoO(2))(av) = 103.5 degrees.     

Determination of stability constants of U(VI), Np(VI) and Pu(VI) with chloride ions by extraction chromatography

The complex formation of U(VI), Np(VI) and Pu(VI) with chloride ions was studied in HClO₄−HCl solutions at ionic strength of 2.0 and [H⁺]=2.0M by the method of extraction chromatography using dilute HDEHP as the stationary phase.     

Stability constants of complexes of uranium/VI/ and plutonium/VI/ with succinate ions

The stability constants of the complexes formed by U/VI/ and Pu/VI/ with succinate ions were determined in 0.5M NaClO₄ medium at 30°C following the Bjerrum-Calvin pH titration technique. The stability constants obtained agreed with values reported in literature following the same technique. The values for the second complexes were reported for the first time. U/VI/ complexes were found to have stabilities higher than the corresponding Pu/VI/ complexes in accordance with the acidities of the cations.     

New polynuclear U(IV)-U(V) complexes from U(IV) mediated uranyl(V) disproportionation

U(IV) promotes the disproportionation of otherwise stable uranyl(V) Schiff base complexes affording U(IV)-U(V) oxo clusters with new geometries and the first example of a U(IV)···UO(2)(+) cation-cation interaction.     

Photoelectron spectra of uranium(IV), (V) and (VI) complexes

Satellites were observed on 4f photoelectron spectra of uranium (IV) complexes, while none was seen for diamagnetic uranyl complexes. Photoelectron lines of oxygen 1s coordinated to the uranium ion were broad for NaUO₃ and uranyl complexes.