Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**

A. Kirstin Sockwell; Teagan F.M. Sweet; Brodie Barth; Sara B. Isbill; Nicole A. DiBlasi; Jennifer E.S. Szymanowski; Ginger E. Sigmon; Allen G. Oliver; Andrew J. Miskowiec; Peter C. Burns; Amy E. Hixon

doi:10.1002/chem.202301164

Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**

A. Kirstin Sockwell, Teagan F.M. Sweet, Brodie Barth, Sara B. Isbill, Nicole A. DiBlasi, Jennifer E.S. Szymanowski, Ginger E. Sigmon, Allen G. Oliver, Andrew J. Miskowiec, Peter C. Burns, Amy E. Hixon

Materials & Chemistry Group

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

Plutonium(IV) oxalate hexahydrate (Pu(C₂O₄)₂ ⋅ 6 H₂O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C₂O₄)₂ ⋅ 6 H₂O; NpOx) and uranium(IV) oxalate hexahydrate (U(C₂O₄)₂ ⋅ 6 H₂O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C₂O₄)₂ ⋅ 6 H₂O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field.

Original language	English
Article number	e202301164
Journal	Chemistry - A European Journal
Volume	29
Issue number	47
DOIs	https://doi.org/10.1002/chem.202301164
State	Published - Aug 21 2023

Funding

We thank the K. Knope at Georgetown University for providing the UCl4 needed to synthesize UOx. The plutonium oxalate work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Heavy Element Program under Award Number DE-SC0018231, whereas the thorium, uranium, and neptunium oxalate work was supported by internal funding through the University of Notre Dame. A.K.S. and J.E.S.S. were supported by funding from the DOE National Nuclear Security Administration (NNSA) under award number DE-NA0003763. T.F.M.S. was supported by a Nuclear Energy Graduate Fellowship through the DOE Office of Nuclear Energy (NE) University Nuclear Leadership Program (UNLP). N.A.D. was supported by the DOE Scholars Program, administered by the Oak Ridge Institute for Science and Education, and funded by the Waste Isolation Pilot Plant project (DOE-CBFO). S.B.I. and A.J.M. were supported by the DOE-NNSA. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under contract DE-AC05-00OR22725. We thank the K. Knope at Georgetown University for providing the UCl needed to synthesize UOx. The plutonium oxalate work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Heavy Element Program under Award Number DE‐SC0018231, whereas the thorium, uranium, and neptunium oxalate work was supported by internal funding through the University of Notre Dame. A.K.S. and J.E.S.S. were supported by funding from the DOE National Nuclear Security Administration (NNSA) under award number DE‐NA0003763. T.F.M.S. was supported by a Nuclear Energy Graduate Fellowship through the DOE Office of Nuclear Energy (NE) University Nuclear Leadership Program (UNLP). N.A.D. was supported by the DOE Scholars Program, administered by the Oak Ridge Institute for Science and Education, and funded by the Waste Isolation Pilot Plant project (DOE‐CBFO). S.B.I. and A.J.M. were supported by the DOE‐NNSA. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under contract DE‐AC05‐00OR22725. 4

Keywords

actinides
carboxylate ligands
coordination modes
structure elucidation
transuranium elements

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10.1002/chem.202301164

Cite this

Sockwell, A. K., Sweet, T. F. M., Barth, B., Isbill, S. B., DiBlasi, N. A., Szymanowski, J. E. S., Sigmon, G. E., Oliver, A. G., Miskowiec, A. J., Burns, P. C., & Hixon, A. E. (2023). Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**. Chemistry - A European Journal, 29(47), Article e202301164. https://doi.org/10.1002/chem.202301164

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title = "Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**",

abstract = "Plutonium(IV) oxalate hexahydrate (Pu(C2O4)2 ⋅ 6 H2O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C2O4)2 ⋅ 6 H2O; NpOx) and uranium(IV) oxalate hexahydrate (U(C2O4)2 ⋅ 6 H2O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C2O4)2 ⋅ 6 H2O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field.",

keywords = "actinides, carboxylate ligands, coordination modes, structure elucidation, transuranium elements",

author = "Sockwell, {A. Kirstin} and Sweet, {Teagan F.M.} and Brodie Barth and Isbill, {Sara B.} and DiBlasi, {Nicole A.} and Szymanowski, {Jennifer E.S.} and Sigmon, {Ginger E.} and Oliver, {Allen G.} and Miskowiec, {Andrew J.} and Burns, {Peter C.} and Hixon, {Amy E.}",

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year = "2023",

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Sockwell, AK, Sweet, TFM, Barth, B, Isbill, SB, DiBlasi, NA, Szymanowski, JES, Sigmon, GE, Oliver, AG, Miskowiec, AJ, Burns, PC & Hixon, AE 2023, 'Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**', Chemistry - A European Journal, vol. 29, no. 47, e202301164. https://doi.org/10.1002/chem.202301164

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T1 - Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures

T2 - A Case for Alternate Coordination Geometries**

AU - Sockwell, A. Kirstin

AU - Sweet, Teagan F.M.

AU - Barth, Brodie

AU - Isbill, Sara B.

AU - DiBlasi, Nicole A.

AU - Szymanowski, Jennifer E.S.

AU - Sigmon, Ginger E.

AU - Oliver, Allen G.

AU - Miskowiec, Andrew J.

AU - Burns, Peter C.

AU - Hixon, Amy E.

PY - 2023/8/21

Y1 - 2023/8/21

N2 - Plutonium(IV) oxalate hexahydrate (Pu(C2O4)2 ⋅ 6 H2O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C2O4)2 ⋅ 6 H2O; NpOx) and uranium(IV) oxalate hexahydrate (U(C2O4)2 ⋅ 6 H2O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C2O4)2 ⋅ 6 H2O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field.

AB - Plutonium(IV) oxalate hexahydrate (Pu(C2O4)2 ⋅ 6 H2O; PuOx) is an important intermediate in the recovery of plutonium from used nuclear fuel. Its formation by precipitation is well studied, yet its crystal structure remains unknown. Instead, the crystal structure of PuOx is assumed to be isostructural with neptunium(IV) oxalate hexahydrate (Np(C2O4)2 ⋅ 6 H2O; NpOx) and uranium(IV) oxalate hexahydrate (U(C2O4)2 ⋅ 6 H2O; UOx) despite the high degree of unresolved disorder that exists when determining water positions in the crystal structures of the latter two compounds. Such assumptions regarding the isostructural behavior of the actinide elements have been used to predict the structure of PuOx for use in a wide range of studies. Herein, we report the first crystal structures for PuOx and Th(C2O4)2 ⋅ 6 H2O (ThOx). These data, along with new characterization of UOx and NpOx, have resulted in the full determination of the structures and resolution of the disorder around the water molecules. Specifically, we have identified the coordination of two water molecules with each metal center, which necessitates a change in oxalate coordination mode from axial to equatorial that has not been reported in the literature. The results of this work exemplify the need to revisit previous assumptions regarding fundamental actinide chemistry, which are heavily relied upon within the current nuclear field.

KW - actinides

KW - carboxylate ligands

KW - coordination modes

KW - structure elucidation

KW - transuranium elements

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JO - Chemistry - A European Journal

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ER -

Insight into the Structural Ambiguity of Actinide(IV) Oxalate Sheet Structures: A Case for Alternate Coordination Geometries**

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Keywords

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