Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18

Niko T Flosbach; Maxim Bykov; Elena Bykova; Bertold Rasche; Mohamed Mezouar; Timofey Fedotenko; Stella Chariton; Vitali B Prakapenka; Mathias S Wickleder

doi:10.1021/acs.inorgchem.3c03948

Stabilization of Pr⁴⁺ in Silicates─High-Pressure Synthesis of PrSi₃O₈ and Pr₂Si₇O₁₈

Inorg Chem. 2024 Mar 18;63(11):4875-4882. doi: 10.1021/acs.inorgchem.3c03948. Epub 2024 Feb 27.

Authors

Niko T Flosbach¹, Maxim Bykov^{1

2}, Elena Bykova³, Bertold Rasche⁴, Mohamed Mezouar⁵, Timofey Fedotenko⁶, Stella Chariton⁷, Vitali B Prakapenka⁷, Mathias S Wickleder¹

Affiliations

¹ Institute of Inorganic Chemistry, University of Cologne, Greinstraße 6, 50939 Cologne, Germany.
² Institute of Inorganic and Analytical Chemistry, Goethe University Frankfurt, Max-von-Laue-Straße 7, 60438 Frankfurt am Main, Germany.
³ Institute of Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt am Main, Germany.
⁴ Institute of Inorganic Chemistry, University of Stuttgart, 70569 Stuttgart, Germany.
⁵ European Synchrotron Radiation Facility (ESRF), Avenue des Martyrs 71, 38000 Grenoble, France.
⁶ Deutsches Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg, Germany.
⁷ Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States.

PMID: 38412505
DOI: 10.1021/acs.inorgchem.3c03948

Abstract

The reaction between PrO₂ and SiO₂ was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr₂^III(Si₂O₇), whereas Pr₄^IIISi₃O₁₂ and Pr₂^IV(O₂)O₃ were obtained at 15 GPa. Pr₄^IIISi₃O₁₂ can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr₄^III(SiO₄)₃. Pr^IVSi₃O₈ and Pr₂^IVSi₇O₁₈ that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both Pr^IVSi₃O₈ and Pr₂^IVSi₇O₁₈. Both silicates are the first structurally characterized representatives of Pr⁴⁺-containing salts with oxoanions. All three silicates contain condensed networks of [SiO₆] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.