First principles investigation of the structural and bonding properties of hydrated actinide (IV) oxalates, An(C2O4)2·6H2O (An = U, Pu)

Garrett, Kerry E.; Ritzmann, Andrew M.; Smith, Frances N.; Devanathan, Ram; Henson, Neil J.; Abrecht, David G.

doi:10.1016/j.commatsci.2018.06.033

Cited by 10 publications

(15 citation statements)

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“…The most informative descriptions on this topic have derived structural details from geometrically-optimized computational models that -with the exception of Pu(C2O4)2•6H2O and Pu(C2O4)2•2H2O, which have published pXRD patterns -have not been experimentally verified. [7,10,13,15,16] In fact, a 2021 density functional theory (DFT) study of Pu(C2O4)2 decomposition clearly states that the precise structural modifications occurring during thermal decomposition of Pu(C2O4)2 have not been experimentally characterized, but the DFTderived intermediate structures should be identifiable using spectroscopic techniques. [10] Despite over 80 years of research involving the Pu(IV) oxalate method, no Raman spectra of Pu(C2O4)2•6H2O or its degradation products have been reported; the lone exception is the Raman spectrum of the terminal degradation product, PuO2.…”

Section: Introductionmentioning

confidence: 99%

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Christian

Foley

Ciprian

et al. 2022

Journal of Nuclear Materials

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Section: Introductionmentioning

confidence: 99%

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Christian

Foley

Ciprian

et al. 2022

Journal of Nuclear Materials

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“…The bonding properties of An(IV)-oxalates have been investigated only with U and Pu in hydrated actinide(IV) oxalates An(C 2 O 4 ) 2 ·6H 2 O using plane-wave calculations, and it was suggested that the uranium–oxalate bond is more ionic than the plutonium–oxalate bond . The scarcity of studies concerning the description of the An(IV)–oxalate bond is associated with the difficulties of dealing with polymeric structures in the computations, while monomeric and molecular structures are good candidates.…”

Section: Introductionmentioning

confidence: 99%

“…The bonding properties of An(IV)-oxalates have been investigated only with U and Pu in hydrated actinide(IV) oxalates An(C 2 O 4 ) 2 •6H 2 O using plane-wave calculations, and it was suggested that the uranium−oxalate bond is more ionic than the plutonium−oxalate bond. 34 The scarcity of studies concerning the description of the An(IV)−oxalate bond is associated with the difficulties of dealing with polymeric structures in the computations, while monomeric and molecular structures are good candidates. Hereafter, we present molecular DFT calculations performed on the homoleptic molecular anions [An(C 2 O 4 ) 5 ] 6− and these results are compared to the hexanitrato An(IV) series [(C 2 H 5 ) 4 N] 2 [An(NO 3 ) 6 ] (with An IV = Th IV , U IV , Np IV , and Pu IV ), which similarly contains only bidentate O-donor ligands but with a greater coordination number (12 versus 10 for oxalate).…”

Section: ■ Introductionmentioning

confidence: 99%

Structural and Bonding Analysis in Monomeric Actinide(IV) Oxalate from Th(IV) to Pu(IV): Comparison with the An(IV) Nitrate Series

et al. 2022

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Single-crystal X-ray diffraction (SC-XRD) structures and Raman spectra of a series of new isomorphous molecular An(IV)-oxalate compounds (Th, U, Np, and Pu) are reported. These complexes are crystallized with cobalt(III) hexamine ([Co(NH 3 ) 6 ] 3+ ) as the counter cations, [Co(NH 3 ) 6 ] 2 [An(C 2 O 4 ) 5 ]•4H 2 O, revealing five bidentate nonbridging oxalate ligands in the first coordination sphere (CN = 10). The nonbridging oxalate is rather uncommon for An(IV)-oxalate systems, which are widely characterized as polymeric compounds. Density functional theory (DFT) calculations were performed to examine the bonding between An(IV) cations and oxalate ligands. For comparison, we also report results obtained for the An(IV)-hexanitrate series, [(C 2 H 5 ) 4 N] 2 [An(NO 3 ) 6 ] (with An = Th, U, Np, Pu, and Ce), which consists of O-donor ligands as well but with a larger coordination number (CN = 12). The bonding analysis confirms that the actinide−oxygen bond is predominantly ionic with a minor increase in covalency from Th to U and slight variations from U to Pu. Further comparison showed that the charge transfer increases slightly when increasing the number of anions in the coordination sphere (C 2 O 4 2− : CN = 10; NO 3 − : CN = 12), but covalent effects as indicated by the amount of internuclear electron density accumulation are small and similar for oxalate and nitrate.

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“…The lattice parameters and interatomic distances derived from our modeling procedure (PW1PW functional) deviate from crystallographic values at most by 1.9% and 2.3% for pyrite, 1.7% and 2.7% for marcasite (orthorhombic FeS 2 ), 0.8% and 1.9% for arsenopyrite (FeAsS), 1.4% and 2.5% for löllingite (orthorhombic FeAs 2 ), 0.16% and 5.03% for dzharkenite (cubic FeSe 2 ) (Tables S8–S14). The errors are typical of DFT GGA studies. ,− The distributions of As and Se were modeled in two supercells of dimensions 2 × 2 × 2 and 3 × 2 × 2. The reciprocal space integration was performed by sampling the Brillouin zone with the 6 × 6 × 6 Pack-Monkhorst mesh, resulting in 112 independent k points.…”

Section: Materials and Methodsmentioning

confidence: 99%

The Mode of Incorporation of As(-I) and Se(-I) in Natural Pyrite Revisited

Manceau

Merkulova

Mathon

et al. 2020

ACS Earth Space Chem.

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Pyrite (FeS2) from coal, sedimentary rocks, and hydrothermal ore deposits generally contains hazardous selenium (Se) and arsenic (As) that are released in natural waters through oxidative dissolution of the host. Knowing how As and Se are structurally incorporated into pyrite has important implication in controlling or preventing their release because trace metal(loid) substitution accelerates the dissolution of pyrite. Previous extended X-ray absorption fine structure (EXAFS) studies have reported that nominally monovalent arsenic clusters at the sulfur site forming As-As pairs at 3.2 Å, whereas monovalent Se does not form Se-Se pairs at this distance for unknown reason. Here, we revisit this question using As and Se K-edge X-ray absorption near-edge structure (XANES) and EXAFS spectroscopy complemented with atomistic calculations. We find that neither As nor Se atoms can be differentiated from S atom at 3.2-3.3 Å, the cluster and dilute model-fits to As-and Se-EXAFS data yielding equivalent least-squares solutions. Thermodynamic calculations of Fe48As3S93 (3.8 wt.% As) and Fe48Se3S93 (4.0 wt.% Se) structures show that the formation of As-As pairs is energetically favorable and the formation of Se-Se pairs unfavorable. Thus, the equilibrium distribution of As and Se predicted by calculation agrees with published EXAFS data. However, this agreement is incidental because EXAFS fits are ambiguous, the same EXAFS spectra being fit indifferently with a cluster and 2 a dilute model. Regarding Se, the dilute model-fit is probably correct since Se-Se pairs are precluded thermodynamically. The situation is less clear for As. The lowest energy atomic arrangement of As in Fe48S93As3 is similar to the local structure of As in arsenopyrite (FeAsS), thus supporting the cluster model. However, the energy gain to total energy provided by the formation of As clusters decreases with decreasing As concentration, making them thermodynamically less favorable below 1.0 wt.%.

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First principles investigation of the structural and bonding properties of hydrated actinide (IV) oxalates, An(C2O4)2·6H2O (An = U, Pu)

Cited by 10 publications

References 50 publications

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Structural and Bonding Analysis in Monomeric Actinide(IV) Oxalate from Th(IV) to Pu(IV): Comparison with the An(IV) Nitrate Series

The Mode of Incorporation of As(-I) and Se(-I) in Natural Pyrite Revisited

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First principles investigation of the structural and bonding properties of hydrated actinide (IV) oxalates, An(C2O4)2·6H2O (An = U, Pu)

Cited by 10 publications

References 50 publications

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

Structural and Bonding Analysis in Monomeric Actinide(IV) Oxalate from Th(IV) to Pu(IV): Comparison with the An(IV) Nitrate Series

The Mode of Incorporation of As(-I) and Se(-I) in Natural Pyrite Revisited

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First principles investigation of the structural and bonding properties of hydrated actinide (IV) oxalates, An(C2O4)2·6H2O (An = U, Pu)