[en] In deep storage technetium can exist in degree IV or III. Recent studies on Tc(IV) have shown that Tc_nO_y^(4n-2y)+, Tc^IV(μ-O)₂Tc^IV structure, is a precursor for precipitation of TcO₂. Few data are available on Tc_nO_y^(4n-2y)+ Subject of this thesis is the mechanism of condensation of Tc(IV) leading to this form. Kinetic studies have shown that the condensation of Tc^IVCl₅(H₂O)^- in chloride media leads to a dimer. XAS studies resulted in a linear structure Tc^IV-O-Tc^IV. This compound, formulated as Tc₂OCl₁₀^4-, is stable at pH = 0.3, it undergoes cyclization to Tc_nO_y^(4n-2y)+ at pH =1.5 and is oxidized to TcO₄^- under α radiation. In 3 M chloride media, TcO₂ lead to formation Tc₂OCl₁₀^4- at pH = 0.3 and to Tc_nO_y^(4n-2y)+ at pH = 1.5. An electrochemical cell permitting 'in situ' XAS measurement was developed. XANES studies have shown that the reduction of Tc(VII) lead to a Tc(IV)/Tc(III) mixture. (author)

[en] The compound (n-Bu₄N)₂Tc₂Br₈ was prepared by the metathesis of (n-Bu₄N)₂Tc₂Cl₈ with HBr (g) in dichloromethane and characterized by X-ray absorption fine structure spectroscopy and UV-vis spectroscopy. Analysis of the data gives a Tc-Tc distance of 2.16(1) (angstrom) and a Tc-Br distance of 2.48(1) (angstrom). The Tc(III) oxidation state was inferred by the position of the edge absorption, which reveals a shift of 12 eV between (n-Bu₄N)₂Tc₂Br₈ and NH₄TcO₄. The analogous shift between (n-Bu₄N)₂Tc₂Cl₈ and NH₄TcO₄ is 11 eV. The UV-vis spectrum of Tc₂Br₈^2- in dichloromethane exhibits the characteristic (delta) → (delta)* transition at 13717 cm^-1. The M₂X₈^2- (M = Re, Tc; X = Cl, Br) UV-vis spectra are compared, and the position of the (delta) → (delta)* transition discussed

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[en] Reductive nitrosylation and complexation of ammonium pertechnetate by acetohydroxamic acid has been achieved in aqueous nitric and perchloric acid solutions. The kinetics of the reaction depend on the relative concentrations of the reaction components and are accelerated at higher temperatures. The reaction does not occur unless conditions are acidic. Analysis of the X-ray absorption fine structure spectroscopic data is consistent with a pseudo-octahedral geometry and the linear Tc-N-O bond typical of technetium nitrosyl compounds, and electron spin resonance spectroscopy is consistent with a d⁵ Tc(II) nitrosyl complex. The nitrosyl source is generally AHA, but it may be augmented by some products of the reaction with nitric acid. The resulting low-valency trans-aquonitrosyl(diacetohydroxamic)-technetium(II) complex ([Tc^II(NO)(AHA)₂H₂O]⁺, 1) is highly soluble in water, extremely hydrophilic, and is not extracted by tri-n-butylphosphate in a dodecane diluent. Its extraction properties are not pH-dependent: potentiometric-spectrophotometric titration studies indicate a single species from pH 4 down to -0.6 (calculated). This molecule is resistant to oxidation by H₂O₂, even at high pH, and can undergo substitution to form other technetium nitrosyl complexes. The potential formation of 1 during reprocessing may strongly impact the fate of technetium in the nuclear fuel cycle

[en] The chemical shift of the X-ray absorption K-edge of Tc(IV) complexes determined by X-ray absorption spectroscopy (XAS) measurement was studied. A correlation between edge position (ΔE) and partial charge on Tc atoms (δ_Tc) was determined. This correlation was used to determinate δ_Tc in Tc_nO_y^(4n-2y)+. Furthermore, a theoretical relation between δ_Tc and the charge of Tc_nO_y^(4n-2y)+, was also established and the overall charge of this complex was estimated. (orig.)

[en] In order to study the stability of Tc(IV) complexes in chloride media under alpha radiation produced by a cyclotron, an electrochemical cell was developed. In this cell, the stability of TcCl₆^2-, TcCl₅(H₂O)^-, Tc₂OCl₁₀^4-, Tc_nO_y^(4n-2y)+ and TcO₂.xH₂O were studied in 3 M chloride media with a pH range from 0.3 to 2.5. The stability of a (TcCl₆^2-/TcCl₅(H₂O)^-/Tc₂OCl₁₀^4-) mixture was also investigated during alpha irradiation under a constant current. These studies showed that TcCl₆^2- is a very stable compound whereas chloro-oxygenated compounds were oxidized to Tc(VII). Consequently, the relative stabilities of the Tc(IV) complexes in 3 M chloride media under alpha irradiation was determined. (author)

[en] A method for speciation of Tc(IV) species (TcCl₆^2- and TcCl₅(H₂O)^-) in chloride solutions, using capillary electrophoresis (CE) technique was developed. The proposed method has overcome the difficulties of unstable oxidation states analysis by shortening their travel time in the capillary. TcCl₆^2- and TcCl₅(H₂O)^- were thus separated without being hydrolyzed and polymerized, and their UV/Vis spectra were recorded. With a 1 M HCl/NaCl buffer solution (pH = 1), the electrophoretic mobilities were determined as 5.47 x 10^-4 cm²/Vs for TcCl₆^2- and 2.13 x 10^-4 cm²/Vs for TcCl₅(H₂O)^- at 25 C. The total analysis time for one run is 12 minutes. (orig.)

[en] A novel dry synthesis for the uranium(VI) dioxo-diacetohydroxamate (UAHA) complex has been developed. The complex was generated in > 80% yield by mechanically grinding solid uranyl acetate dihydrate (UAc) with solid acetohydroxamic acid in stoichiometric amounts. The resulting UO₂(AHA)₂.4H₂O solid is purified by washing with acetone. The stoichiometry was confirmed via colorimetric assays for U(VI) and AHA. The stoichiometry was confirmed via colorimetric assays for U(VI) and AHA. The analogous ferric trisacetohydroxamate complex (FeAHA) was synthesized for comparison. The UAHA solid was extensively characterized by ultraviolet-visible (UV-vis), Fourier-transform infrared (FT-IR), and extended X-ray absorption fine structure (EXAFS) spectroscopies. The compound did not fluoresce after laser excitation. Proton nuclear magnetic resonance (NMR) spectra were obtained of the complex in D₂O, acidified acetonitrile-d₃, and DMSO-d₆. The solubility was determined over a range of solvents. It was determined that in the purified solid, two bidentate AHA molecules bind to uranyl via the carbonyl and hydroxamate oxygen atoms, a structure analogous to known ferric, nickel, and lanthanum AHA complexes. In an acidic environment, binding is monodentate through the hydroxamate oxygen. And in aqueous solution, the UAHA complex assumes both binding moieties, depending on the pH. This pH-dependent speciation change is demonstrated for the first time. The easy synthesis and purification of UAHA enables researchers to strictly control reaction conditions; to eliminate interfering salts and water; and to study the complex in the solid-phase. (orig.)

[en] The stabilities of the technetium polymers: Tc₂OCl₁₀^4- and Tc_nO_y^4n-2y+ have been studied under light irradiation in 3 M chloride media with a pH range from 0 to 1.3. It has been shown that under irradiation, Tc₂OCl₁₀^4- is not stable and undergoes dissociation to TcCl₅(H₂O)^- at pH = 0 and pH = 0.3. At pH = 1, irradiation of Tc₂OCl₁₀^4- leads to a stationary state involving TcCl₅(H₂O)^- and Tc₂OCl₁₀^4-. At pH = 1.3, Tc_nO_y^4n-2y+ remains stable under irradiation. Under light irradiation, the predominance diagram of Tc(IV) species obtained from Tc₂OCl₁₀^4- aquation in a pH range from 0 to 1 is drawn. The chemical behaviour of Tc₂OCl₁₀^4- and the influence of the light on the condensation of Tc(IV) and solubility of TcO₂.xH₂O are discussed. (orig.)

[en] In the context of the immobilization of technetium, as pertechnetate, from spent nuclear fuel from reprocessing activities, or potentially a scavenger for pertechnetate in repository conditions, the compound tetraphenylpyridinium pertechnetate (TPPy-TcO₄) has been synthesized, structurally characterized and its solubility investigated. The compound TPPy-TcO₄ has been prepared by metathesis from ammonium pertechnetate and 1,2,4,6-tetraphenylpyridinium tetrafluoroborate from a water/acetone media. Diffraction measurements show that the compound crystallizes in the orthorhombic space group (Pbca) with a = 16.1242(10) A, b = 16.7923(10) A, and c = 17.6229(11) A. The solubility of the salt has been investigated at room temperature in aqueous media at pH 2.22, 6.91, and 9.81 where solubility products were determined as 6.16 x 10^-12, 4.13 x 10^-12, and 1.16 x 10^-11, respectively. The compound TPPy-TcO₄ is not the most insoluble pertechnetate salt reported so far, but comparatively has a lower solubility than that of most other pertechnetate salts. (orig.)