Chemical State of U in U–N–O Ternary System from First-Principles Calculations

Wang, Xin; Qiu, Ruizhi; Zhong, Ling; Lu, Linfeng; Hu, Yin; Liu, Kezhao; Zhang, Pengcheng

doi:10.1021/acs.jpcc.9b04288

Cited by 9 publications

(6 citation statements)

References 53 publications

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“…However, in the present EXAFS evaluation, the very short interatomic distances associated with a U(VI) character were not reproduced, which indicates that the geometry of the cuboctahedral oxygen clusters needs to be re-evaluated. Our results support the latest insights obtained from experiments and calculations, which agree on the occurrence of only U(IV) and U(V) environments in U 3 O 7 , , thus solving the ambiguity concerning the valence state determination. , …”

Section: Discussionsupporting

confidence: 88%

“…In contrast, according to results obtained from total reflection X-ray fluorescence (TXRF)-XANES at the U L 3 -edge, a distribution of 2×U(IV) + 1×U(VI) was found to be marginally favorable over the alternative . However, recent calculations have also reproduced the 1×U(IV) + 2×U(V) distribution in U 3 O 7 , , as determined from the U M 4 -edge data …”

Section: Introductionmentioning

confidence: 88%

“…25 In contrast, according to results obtained from total reflection Xray fluorescence (TXRF)-XANES at the U L 3 -edge, a distribution of 2×U(IV) + 1×U(VI) was found to be marginally favorable over the alternative. 26 However, recent calculations have also reproduced the 1×U(IV) + 2×U(V) distribution in U 3 O 7 , 27,28 as determined from the U M 4 -edge data. 25 In the current work, the remaining ambiguity concerning the valence distribution in U 3 O 7 is finally resolved by discussing new HERFD-XANES data, and additionally, by evaluating the EXAFS.…”

Section: Introductionmentioning

confidence: 99%

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Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇

et al. 2020

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A comprehensive analysis of X-ray absorption data obtained at the U L 3-edge for a systematic series of single-valence (UO2, KUO3, UO3) and mixed-valence uranium compounds (U4O9, U3O7, U3O8) is reported. High-energy resolution fluorescence detection (HERFD) X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) methods were applied to evaluate U(IV) and U(V) environments, and in particular, to investigate the U3O7 local structure. We find that the valence state distribution in mixed-valence uranium compounds cannot be confidently quantified from a principal component analysis of the U L 3-edge XANES data. The spectral line broadening, even when applying the HERFD-XANES method, is sensibly higher (∼3.9 eV) than the observed chemical shifts (∼2.4 eV). Additionally, the white line shape and position are affected not only by the chemical state, but also by crystal field effects, which appear well-resolved in KUO3. The EXAFS of a phase-pure U3O7 sample was assessed based on an average representation of the expanded U60O140 structure. Interatomic U–O distances are found mainly to occur at 2.18 (2), 2.33 (1), and 3.33 (5) Å, and can be seen to correspond to the spatial arrangement of cuboctahedral oxygen clusters. The interatomic distances derived from the EXAFS investigation support a mixed U(IV)–U(V) valence character in U3O7.

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Section: Discussionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

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Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇

et al. 2020

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“…The shift of the N–N vibrations to lower frequency upon binding to a metal ion has been seen previously for transition metal ion–nitrogen complexes ,, and for neutral U(N 2 ) n , UN(N 2 ) n , and NUN(N 2 ) n complexes in matrix isolation experiments . This red-shift is explained by using the Dewar–Chatt–Duncanson model of metal–ligand charge transfer and is analogous to the shifts seen for many metal–carbonyl complexes. In the case of metal–carbonyls, there is a competition between ligand → metal σ-donation, which leads to higher frequencies, and metal → ligand π back-bonding, which leads to lower frequencies. In the case of metal–nitrogen complexes, both effects tend to lower the N–N stretch frequency, as seen here.…”

Section: Results and Discussionsupporting

confidence: 72%

Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes

et al. 2021

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Laser vaporization of uranium in a pulsed supersonic expansion of nitrogen is used to produce complexes of the form U + (N 2 ) n (n = 1−8). These ions are mass selected in a reflectron time-of-flight spectrometer and studied with visible and UV laser fixed-frequency photodissociation and with tunable infrared laser photodissociation spectroscopy. The dissociation patterns and spectroscopy of U + (N 2 ) n indicate that N 2 ligands are intact molecules and that there is no insertion chemistry resulting in UN + or NUN + . Fixed frequency photodissociation at 532 and 355 nm indicate that the U + −N 2 bond dissociation energy varies little with changing coordination. The photon energy and the number of ligands eliminated allow an estimate of the average U + −N 2 dissociation energy of 12 kcal/mol. Infrared bands are observed for these complexes near the N−N stretch vibration via elimination of N 2 molecules. These resonances are observed to be shifted about 130 cm −1 to the red from the free-N 2 frequency for complexes with n = 3−8. Density functional theory indicates that U + is most stable in the sextet state in these complexes and that N 2 molecules bind in end-on configurations. The fully coordinated complex is predicted to be U + (N 2 ) 8 , which has a cubic structure. The vibrational frequencies predicted by theory are consistently lower than those in the experiment, independent of the isomeric structure or spin state of the complexes. Despite its failure to reproduce the infrared spectra, theory provides an average U + −N 2 dissociation energy of 11.8 ± 0.5 kcal/mol, in good agreement with the value from the experiments.

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“…The oxidation state can then be assigned with knowledge of the number of d electrons in the ion. The method has been applied successfully to study the oxidation states of transition metal ions in various problems (Sit et al, 2012;Majumdar et al, 2017;Wei et al, 2017;Ku and Sit, 2019;Ricca et al, 2019;Wang et al, 2019;Jensen et al, 2020). Further details of this method can be found in Sit et al (2011).…”

Section: Computational Methodologymentioning

confidence: 99%

Formation of Humboldtine During the Dissolution of Hematite in Oxalic Acid – Density Functional Theory (DFT) Calculations and Experimental Verification

Vehmaanperä

Gong

Sit

et al. 2021

Clays and clay miner.

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Understanding the reactions taking place in the hematite-oxalic acid system is important in order to clean iron oxides from filters and to remove iron from mineral concentrates. Previous studies reported the formation of an unwanted solid phase during this process. The objective of the current work, therefore, was to visualize and rationalize the iron dissolution steps taking place in the hematite–oxalic acid reaction by combining density functional theory (DFT) calculations and experimental data. The results of DFT calculations indicated that a precipitate was formed in this reaction; XRD analysis of the solid phase after the dissolution experiment revealed the formation of humboldtine as the precipitate. The attachment of oxalate on the hematite surface and the reduction of Fe(III) to Fe(II) were key steps for humboldtine formation. Both simulations and the experimental results showed that greater oxalic acid concentrations yielded more precipitate, suggesting a simple and novel route to synthesize humboldtine, a material which is relevant to the demand for clean energy.

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Chemical State of U in U–N–O Ternary System from First-Principles Calculations

Cited by 9 publications

References 53 publications

Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇

Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇

Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes

Formation of Humboldtine During the Dissolution of Hematite in Oxalic Acid – Density Functional Theory (DFT) Calculations and Experimental Verification

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Chemical State of U in U–N–O Ternary System from First-Principles Calculations

Cited by 9 publications

References 53 publications

Local Structure in U(IV) and U(V) Environments: The Case of U3O7

Local Structure in U(IV) and U(V) Environments: The Case of U3O7

Photodissociation and Infrared Spectroscopy of Uranium–Nitrogen Cation Complexes

Formation of Humboldtine During the Dissolution of Hematite in Oxalic Acid – Density Functional Theory (DFT) Calculations and Experimental Verification

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Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇

Local Structure in U(IV) and U(V) Environments: The Case of U₃O₇