Title: Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters

Abstract

Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO₂)₂₄(O₂)₂₄(P₂O₇)₁₂]^48– ({U₂₄Pp₁₂}), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral (O_h) molecular symmetry. One-dimensional ³¹P NMR experiments provide direct evidence that both K⁺ and Rb⁺ ions trigger an O_h-to-D_4h conformational change within {U₂₄Pp₁₂}. Variable-temperature ³¹P NMR experiments conducted on partially titrated {U₂₄Pp₁₂} systems show an effect on the rates; increased activation enthalpy and entropy for the D_4h-to-O_h transition is observed in the presence of Rb⁺ compared to K⁺. Two-dimensional, exchange spectroscopy ³¹P NMR revealed that magnetization transfer links chemically unique Pp bridges that are present in the D_4h conformation and that this magnetization transfer occurs via a conformational rearrangement mechanism as the bridges interconvert between two symmetries. The interconversion is triggered by the departure and reentry of K (or Rb) cations out of and into the cavity of the cluster. This rearrangement allows Pp bridges to interconvert without the need to break bonds. Cs ions exhibit unique interactions with {U₂₄Pp₁₂} clusters and cause only minor changes in the solution ³¹P NMR signatures, suggesting that O_h symmetry is conserved. Single-crystal X-ray diffraction measurements revealmore » that the mixed Li/Na/Cs salt adopts D_2h molecular symmetry, implying that while solvated, this cluster is in equilibrium with a more symmetric form. Thus, these results highlight the unusually flexible nature of the actinide-based {U₂₄Pp₁₂} and its sensitivity to countercations in solution.« less

Authors:

Dembowski, Mateusz  ^[1];

• Search DOE PAGES for author "Dembowski, Mateusz"
• Search DOE PAGES for ORCID "0000-0002-6665-8417"

Pilgrim, Corey D. ^[2]; Hickam, Sarah ^[1]; Spano, Tyler  ^[1];

• Search DOE PAGES for author "Spano, Tyler"
• Search DOE PAGES for ORCID "0000-0001-6572-9722"

Hamlin, Dallas ^[1]; Oliver, Allen G. ^[1]; Casey, William H.  ^[2];

• Search DOE PAGES for author "Casey, William H."
• Search DOE PAGES for ORCID "0000-0002-3275-6465"

Burns, Peter C.  ^[1]

• Search DOE PAGES for author "Burns, Peter C."
• Search DOE PAGES for ORCID "0000-0002-2319-9628"

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+ Show Author Affiliations

1. Univ. of Notre Dame, IN (United States)
2. Univ. of California, Davis, CA (United States)

Publication Date:

Tue Feb 04 00:00:00 EST 2020

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Energy Frontier Research Centers (EFRC) (United States). Materials Science of Actinides (MSA); Univ. of Notre Dame, IN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1649332

Grant/Contract Number:  

AC05-00OR22725; SC0001089

Resource Type:

Accepted Manuscript

Journal Name:

Inorganic Chemistry

Additional Journal Information:

Journal Volume: 59; Journal Issue: 4; Journal ID: ISSN 0020-1669

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Salts; Anions; Conformation; Cluster chemistry; Cations