The importance of accurate crystal structure determination of uranium minerals. II. Soddyite (UO2)2(SiO4).2H2O

Demartin, Francesco; Gramaccioli, C. M.; Pilati, Tullio

doi:10.1107/s0108270191004481

Cited by 65 publications

(60 citation statements)

References 3 publications

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“…In general, the distances deduced from EXAFS were consistent with those obtained from XRD [10,23,24,27]. Further, important aspects of the U(VI) coordination environment were confirmed, in particular the distance between U(VI) and the two axial oxygen atoms and the existence of a split equatorial oxygen shell.…”

Section: U(vi) Reference Compoundssupporting

confidence: 80%

“…A multi shell approach was employed for data fitting. Theoretical single and multiple scattering paths (SS and MS paths, respectively) were calculated using FEFF8.20 [21,22] and the α-uranophane or soddyite structures as model compounds [23,24] respectively. The amplitude reduction factor, S 2 0 , was held constant using a value of 1.0 for all fits.…”

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

“…For example, the coordination number (N) of the first shell was held constant, simulating the axial oxygen atoms of the uranyl structure, as the X-ray absorption near edge structure (XANES) part of the spectra did not indicate any change in the redox state. In case of the U(VI) reference compounds, the coordination numbers of all neighboring atoms were held constant in accordance with the XRD data published in the literature [10,23,24,27]. For each fit, the threshold energy (ΔE 0 ) was linked for all shells and was allowed to vary as a global parameter.…”

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

“…The latter assumption implies that the path length and DW factor of each MS path is related to the SS axial oxygen path. The fitting approach was tested on several reference compounds (soddyite, becquerelite, α-uranophane, CaUO 3.8 and K-boltwoodite) based on the comparison of fitted data with the crystallographic distances reported in the literature [10,23,24,[27][28][29].…”

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

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EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

Macé¹,

Wieland²,

Dähn³

et al. 2013

Radiochimica Acta

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U(VI) / Speciation / Cement / (Micro-)EXAFSSummary. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the coordination environment of U(VI) in cementitious materials. The EXAFS measurements were carried out on U(VI)-doped samples prepared under varying conditions, such as samples from sorption, hydration and diffusion experiments, and using different cementitious materials, such as crushed hardened cement paste (HCP) and calcium silicate hydrates (C-S-H). The samples had U(VI) loadings ranging from 1700 μg/g to 45 000 μg/g. Applying principal component analysis (PCA) on 13 EXAFS spectra (each spectra corresponding to a minimum of five different scans) of the low loading samples, one single species is obtained indicating a similar U(VI) coordination environment for both HCP and C-S-H samples. This result confirms that C-S-H phases control the uptake of U(VI) in the complex cement matrix. The coordination environment of this species is similar to a U(VI) surface complex or to U(VI) in uranyl silicate minerals (two axial O atoms at 1.82 ± 0.02 Å; four equatorial O atoms at 2.25 ± 0.01 Å; one Si atom at 3.10 ± 0.03 Å). At high U(VI) loading, PCA revealed a second U(VI) species, with a coordination environment similar to that of U(VI) in calcium uranate (two axial O atoms at 1.94 ± 0.04 Å; five equatorial O atoms at 2.26 ± 0.01 Å; four Ca atoms at 3.69 ± 0.05 Å and five U atoms at 3.85 ± 0.04 Å).

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Section: U(vi) Reference Compoundssupporting

confidence: 80%

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

Section: Bulk-and μ-Exafs Data Collection and Reductionmentioning

confidence: 99%

See 2 more Smart Citations

EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

Macé¹,

Wieland²,

Dähn³

et al. 2013

Radiochimica Acta

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“…β-uranophane is a polymorph of uranophane (α-uranophane), and the details of their structural connectivities differ substantially 6,8 . Soddyite is characterized by the UO 2 2+ /SiO 2 molar ratio 2:1 and framework crystal structure 6,9 . The crystal structure of Na 2 (UO 2 ) 2 SiO 4 F 2 is structurally related to soddyite 10 .…”

Section: Introductionmentioning

confidence: 99%

Molecular structure of the uranyl silicates—a Raman spectroscopic study

Frost

Čejka

Weier

et al. 2006

J. Raman Spectrosc.

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Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including uranophane, sklodowskite, cuprosklodowskite, boltwoodite and kasolite. Raman spectra clearly show well resolved bands in the 750 to 800 cm -1 region and in the 950 to 1000 cm -1 region assigned to the ν 1 modes of the (UO 2 ) 2+ units and to the (SiO 4 ) 4-tetrahedra. Sets of Raman bands in the 200 to 300 cm -1 region are assigned to ν 2 δ (UO 2 ) 2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of ν 2 δ (UO 2 ) 2+ vibrations. The (SiO 4 ) 4-tetrahedral are characterized by bands in the 470 to 550 cm -1 and in the 390 to 420 cm -1 region. These bands are attributed to the ν 4 and ν 2 (SiO 4 ) 4-bending modes. The minerals show characteristic OH stretching bands in the 2900 to 3500 cm -1 and 3600 to 3700 cm -1 region ascribed to water stretching and SiOH stretching vibrations. The high wavenumber position of the δH 2 O bands indicate strong hydrogen bonding of water in these uranyl silicates. Bands in the 1400 to 1550 cm -1 region are attributed to δSiOH modes. The Raman spectroscopy of uranyl silicate minerals enabled separation of the bands attributed to distinct vibrational units. This enabled definitive assignment of the bands. The spectra are analysed in terms of the molecular structure of the minerals.

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Mechanistic Aspects of the Reaction between Br2 and Chalcogenone Donors (LE; E=S, Se): Competitive Formation of 10-E-3, T-Shaped 1:1 Molecular Adducts, Charge-Transfer Adducts, and [(LE)2]2+ Dications

Aragoni¹,

Arca²,

Demartin

et al. 2001

Chem. Eur. J.

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The synthesis and spectroscopic characterisation of the products obtained by treatment of N,N'-dimethylimidazolidine-2-thione (1), N,N'-dimethylimidazolidine-2-selone (2), N,N'-dimethylbenzoimidazole-2-thione (3) and N,N'-dimethylbenzoimidazole-2-selone (4) with Br2 in MeCN are reported, together with the crystal structures of the 10-E-3, T-shaped adducts 2 . Br2 (12), 3 . Br2 (13) and 4 . Br2 (14). A conductometric and spectrophotometric investigation into the reaction between 1-4 and Br2, carried out in MeCN, allows the equilibria involved in the formation of the isolated 10-E-3 (E = S, Se) hypervalent compounds to be hypothesised. In order to understand the reasons why S and Se donors can give different product types on treatment with Br2 and I2, DFT calculations have been carried out on 1-8, 19 and 20, and on their corresponding hypothetical [LEX]+ cations (L = organic framework; E = S, Se; X = Br, I), which are considered to be key intermediates in the formation of the different products. The results obtained in terms of NBO charge distribution on [LEX]+ species explain the different behaviour of 1-8, 19 and 20 in their reactions with Br2 and I2 fairly well. X-ray diffraction studies show 12-14 to have a T-shaped (10-E-3; E = S, Se) hypervalent chalcogen nature. They contain an almost linear Br-E-Br (E = S, Se) system roughly perpendicular to the average plane of the organic molecules. In 12, the Se atom of each adduct molecule has a short interaction with the Br(1) atom of an adjacent unit, such that the Se atom displays a roughly square planar coordination. The Se-Br distances are asymmetric [2.529(1) vs. 2.608(1) A], the shorter distance being that with the Br(1) atom involved in the short intermolecular contact. In contrast, in the molecular adducts 13 and 14, which lie on a two-fold crystallographic axis, the Br-E-Br system is symmetric and no short intermolecular interactions involving chalcogen and bromine atoms are observed. The adducts are arranged in parallel planes; this gives rise to a graphite-like stacking. The new crystalline modification of 10, obtained from acetonitrile solution, confirms the importance of short intermolecular contacts in determining the asymmetry of Br-E-Br (E = S, Se) and I-Se-I groups in hypervalent 10-E-3 compounds. The analogies in the conductometric and spectrophotometric titrations of 1 and 2-4 with Br2, together with the similarity of the vibrational spectra of 11-14, also imply a T-shaped nature for 11. The vibrational properties of the Br-E-Br (E = S, Se) systems resemble those of the Br3- and IBr2- anions: the Raman spectrum of a symmetric Br-E-Br group shows only one peak near 160 cm(-1), as found for symmetric Br3- and IBr2- anions, while asymmetric Br-E-Br groups also show an antisymmetric Br-E-Br mode at around 190 cm(-1), as observed for asymmetric Br3- and IBr2- ions. Therefore, simple IR and Raman measurements provide a useful tool for distinguishing between symmetric and asymmetric Br-E-Br groups, and hence allow predictions about the crystal packing of th...

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The importance of accurate crystal structure determination of uranium minerals. II. Soddyite (UO2)2(SiO4).2H2O

Cited by 65 publications

References 3 publications

EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

EXAFS investigation on U(VI) immobilization in hardened cement paste: influence of experimental conditions on speciation

Molecular structure of the uranyl silicates—a Raman spectroscopic study

Mechanistic Aspects of the Reaction between Br2 and Chalcogenone Donors (LE; E=S, Se): Competitive Formation of 10-E-3, T-Shaped 1:1 Molecular Adducts, Charge-Transfer Adducts, and [(LE)2]2+ Dications

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