Tc(IV) chemistry in mixed chloride/sulphate acidic media. Formation of polyoxopolymetallic species

Vichot, L.; Fattahi, Massoud; Musikas, C.; Grambow, Bernd

doi:10.1524/ract.91.5.263.20312

Cited by 29 publications

(24 citation statements)

References 19 publications

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“…Upon further irradiation with UV light, these peaks remain intact until 24 hours at which time small features grow in at 320 nm and ca. 500 nm This is consistent with literature studies of reduction of TcO 4 – with gamma irradiation wherein absorption peaks at 320 nm (ε = 6800 m –1 cm –1 ) and a weak absorption at 500 nm (ε = 700 m –1 cm –1 ) that are attributed to Tc IV occur. This is consistent with our XANES control studies where TcO 4 – irradiated in the acidic reduction solution without POM, shows ≤ 20 % Tc IV , confirming that the bulk of the reduced Tc species we see is a result of the POM and not simply the irradiation of TcO 4 – .…”

Section: Resultssupporting

confidence: 91%

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Strategies for the Photoreduction of Tc‐99 Pertechnetate to Low‐Valent Tc by Keggin Polyoxometalates

et al. 2020

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Technetium‐99 (half‐life of 2.1 × 105 yrs, βmax = 0.29 MeV) is a hazardous radiological contaminant, which, in its predominant form of pertechnetate (TcO4–), is highly mobile in the environment. Most strategies for the removal of pertechnetate from the environment involve uptake and/or absorption of pertechnetate using resins, clays, cationic metal‐organic frameworks and even thorium borate ceramic like materials. Alternative approaches have involved the reduction and subsequent sequestration of lower valent technetium species using iron, sulfides, or iron sulfides. Our lab has explored this strategy using the lacunary alpha‐2 Wells–Dawson polyoxometalate (α2‐[P2W17O61]10–) to both reduce and sequester lower valent technetium, and we have reported on the ligand features that stabilize the reduced species. In this work we investigate the potential of “plenary” Keggin POMs (XW12O40n–) (X = P, Si, Al, n = 3, 4, 5, respectively) to both reduce TcO4– and stabilize the reduced Tc species. Specifically, we report on the mechanism by which the reduction of technetium occurs and find that PW12, SiW12, and AlW12 promote the reduction of TcO4– to lower valent states. X‐ray absorption spectroscopy was used to confirm a combination of TcIV {in the form of TcO2·2H2O and Tc2(µ‐O)24+} and TcV, which is subsequently complexed into a POM defect as a TcV=O species.

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Section: Resultssupporting

confidence: 91%

“…The amounts of polymeric Tc IV species increased with increasing dose and 80 % of TcO 4 – was converted to polymeric Tc IV species at 6.5 kGy. TcO 4 – also formed the polymeric species when subjected to electrochemical reduction, as identified by the characteristic absorbances in the UV/Visible spectra and by ITLC.…”

Section: Resultsmentioning

confidence: 95%

Strategies for the Photoreduction of Tc‐99 Pertechnetate to Low‐Valent Tc by Keggin Polyoxometalates

et al. 2020

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“…Moreover, the yellow species is unlikely to be be Tc(IV), Tc(V), or Tc(VI), since in water, Tc(IV) complexes exhibit characteristic spectra, and Tc(V) and Tc(VI) species disproportionate to Tc(IV). [31,26] Excitation energies and oscillator strengths for the lowest-lying excited states of the TcO 3 (OH)(H 2 O) 2 complex were computed using the time-dependent density functional theory (TD-DFT) at the GGA/B3LYP level of theory. Theoretical results are reported in Figure 5 along with the experimental spectrum (cf .…”

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confidence: 99%

Speciation of heptavalent technetium in sulfuric acid: structural and spectroscopic studies

et al. 2010

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Summary. The speciation of Tc(VII) in 12 M sulfuric acid was studied by NMR, UVvisible and XAFS spectroscopy, experimental results were supported by DFT calculation and were in agreement with the formation of TcO 3 OH(H 2 O) 2 .Heptavalent transition metal complexes of group VII with the d 0 electronic configuration are often used in catalysis and biomedical applications. [1,2,3] For manganese, the high electron affinity and oxidation potential of its heptavalent complexes make these species the catalysts of choice for oxidation of organic compounds.[4] The chemistry of Re(VII) complexes has been extensively studied, and species with the ReO 3 + core (e.g., CH 3 ReO 3 ) have been reported to be efficient catalysts. [3] Concerning technetium, its coordination chemistry has mainly been driven by radiopharmaceutical applications. Pentavalent and trivalent Tc complexes have been the most studied while heptavalent coordination complexes are still rare. [5] Permetallates with the tetrahedral geometry are the most common heptavalent species and are stable in aqueous media over a large range of pH and electrochemical potential. [6] In concentrated acid, permetallates are generally unstable and reduction, dimerisation, dehydration or complexation can occur. [7,8,9,10] The reaction of pertechnetate in water with strong acid leads to dehydration and various complexes with TcO 3 + core have been synthesized. [11] In theses synthetic reactions, it is assumed that the anhydrous Tc 2 O 7 is formed as an intermediate product. [11] Sulfuric acid is widely used in industrial applications; it is also a solvent of choice for dehydration process. [12-13] Speciation of Mn(VII) in H 2 SO 4 has been documented; manganese heptoxide is formed after dissolution of KMnO 4 and the MnO 3 + cation has been reported. [14,15,16]. For technetium and rhenium, speciation data are still sparse, the HReO 2 (SO 4 ) 2 .3H 2 O complex has been mentioned while technetium heptoxide has been proposed but no structural nor speciation data were provided. [17][18] In the present work, the speciation of technetium complexes after dissolution of KTcO 4 in sulfuric acid has been performed. The molecular structure and spectroscopic properties of the complexes were studied by UV-visible, X-ray absorption fine structure (XAFS) and NMR spectroscopy and density functional theory (DFT) techniques.Potassium pertechnetate (~ 30 mg) was placed in glass vials, and 1 M, 6 M, 12 M sulfuric acid (5 mL) was added with a glass pipette. After dissolution of the salt, a yellow color is observed in 12 M while for 1 M and 6 M, the solution remains clear. UV-visible spectroscopy measurements in 1 M and 6 M show the presence of TcO 4 -while in 12 M, the spectrum of the yellow solution differs from that of the pertechenate (vide supra). The conditions of formation of the yellow species were investigated by NMR spectroscopy. Technetium samples were prepared in H 2 SO 4 (from 3 M to 18 M) and 99 The 99 Tc NMR data were fit by allowing the pK a s and the chemical shifts of the unprot...

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“…5. The structures (1) to (4) were determined [5,17,18]. That of (6) is not yet known and could be determined by EXAFS.…”

Section: Resultsmentioning

confidence: 99%

“…The redox states VI and V are unstable and disproportionate [3,4]. Polymerised forms of Tc(IV) are stabilised in acidic media around pH = 1 [5].…”

Section: Introductionmentioning

confidence: 99%

Speciation of technetium(IV) chloride under gamma irradiation

Fattahi¹,

Vichot²,

Poineau³

et al. 2005

Radiochimica Acta

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Technetium speciation / Gamma radiolysis / Technetium one-electron oxidation / Radioactive waste disposalSummary. Speciation of Tc in aqueous solution is a complex phenomenon because several parameters intervene simultaneously. We show under gamma radiations, it is completely modified. At pH 8.5 TcO 2 is oxidized to Tc(VII) with a yield of 1.38 × 10 −7 mol J −1 . At pH 1.5, it was demonstrated that Tc is present as hydroxylated species Tc n O y (4n−2y)+ (L. Vichot, M. Fattahi, M. Musikas: Radiochim. Acta 91, 263 (2003)). Its oxidation leads also to Tc(VII) with an experimental yield of 1.45 × 10 −7 mol J −1 . In more acidic solutions, results are consistent with hydrolysis and oxidation of Tc(IV) to Tc(V). As for colloidal solutions of Tc(IV) or TcO 2 , they give Tc(VII) whereas solutions of TcCl 6 2− at pH 0.5 and 1.5 do not lead directly to Tc(VII). Reduced states of Tc are very sensitive to radiation. Hydrolysis as well as polymerisation of Tc are accelerated. Furthermore the radiolytic processes are pH dependent.

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Tc(IV) chemistry in mixed chloride/sulphate acidic media. Formation of polyoxopolymetallic species

Abstract: SummaryThe substitution of the Cl

Cited by 29 publications

References 19 publications

Strategies for the Photoreduction of Tc‐99 Pertechnetate to Low‐Valent Tc by Keggin Polyoxometalates

Strategies for the Photoreduction of Tc‐99 Pertechnetate to Low‐Valent Tc by Keggin Polyoxometalates

Speciation of heptavalent technetium in sulfuric acid: structural and spectroscopic studies

Speciation of technetium(IV) chloride under gamma irradiation

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