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Kretzschmar J, Tsushima S, Lucks C, Jäckel E, Meyer R, Steudtner R, Müller K, Rossberg A, Schmeide K, Brendler V. Dimeric and Trimeric Uranyl(VI)-Citrate Complexes in Aqueous Solution. Inorg Chem 2021; 60:7998-8010. [PMID: 34015210 DOI: 10.1021/acs.inorgchem.1c00522] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This research addresses a subject discussed controversially for almost 70 years. The interactions between the uranyl(VI) ion, U(VI), and citric acid, H3Cit, were examined using a multi-method approach comprising nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis), attenuated total reflectance Fourier-transform infrared (ATR FT-IR), and extended X-ray absorption fine-structure (EXAFS) spectroscopies as well as density functional theory (DFT) calculations. Combining 17O NMR spectroscopy and DFT calculation provided an unambiguous decision on complex configurations, evidencing for the first time that the dimeric complex, (UO2)2(HCit-H)22-, exists as two diastereomers with the syn-isomer in aqueous solution strongly favored over the anti-isomer. Both isomers interconvert mutually with exchange rates of ∼30 s-1 at -6 °C and ∼249 s-1 at 60 °C in acidic solution corresponding to an activation barrier of about 24 kJ mol-1. Upon increasing the pH value, ternary dimeric mono- and bis-hydroxo as well as trimeric complexes form, that is, (UO2)2(HCit-H)2(OH)3-, (UO2)2(HCit-H)2(OH)24-, (UO2)3(O)(Cit-H)38-, and (UO2)3(O)(OH)(Cit-H)25-, respectively. Stability constants were determined for all dimeric and trimeric species, with log β° = -(8.6 ± 0.2) for the 3:3 species being unprecedented. Additionally, in the 6:6 sandwich complex, formed from two units of 3:3 species, the 17O NMR resonance of the trinuclear uranyl(VI) core bridging μ3-O is shown for the first time. Species distribution calculations suggest that the characterized polynuclear U(VI)-citrate species do not significantly increase uranium(VI) mobility in the environment. Furthermore, we revise the misconceptions in the aqueous U(VI)-citric acid solution chemistry, that is, structures proposed and repeatedly taken up, and outline generalized isostructural considerations to provide a basis for future U(VI) complexation studies.
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Affiliation(s)
- Jerome Kretzschmar
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Satoru Tsushima
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany.,World Research Hub Initiative (WRHI), Institute of Innovative Research, Tokyo Institute of Technology, Meguro, 152-8550 Tokyo, Japan
| | - Christian Lucks
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany.,Rossendorf Beamline (ROBL, BM20-CRG), European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, 38043 Grenoble, France
| | - Elisabeth Jäckel
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Ronny Meyer
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Robin Steudtner
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Katharina Müller
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - André Rossberg
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany.,Rossendorf Beamline (ROBL, BM20-CRG), European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, 38043 Grenoble, France
| | - Katja Schmeide
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Vinzenz Brendler
- Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany
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