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Structure and bonding of a radium coordination compound in the solid state

Nature Chemistry volume 16, pages 168–172 (2024)Cite this article

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Abstract

The structure and bonding of radium (Ra) is poorly understood because of challenges arising from its scarcity and radioactivity. Here we report the synthesis of a molecular Ra2+ complex using 226Ra and the organic ligand dibenzo-30-crown-10, and its characterization in the solid state by single-crystal X-ray diffraction. The crystal structure of the Ra2+ complex shows an 11-coordinate arrangement comprising the 10 donor O atoms of dibenzo-30-crown-10 and that of a bound water molecule. Under identical crystallization conditions, barium (Ba2+) yielded a 10-coordinate ‘Pac-Man’-shaped structure lacking water. Furthermore, the bond distance between the Ra centre and the O atom of the coordinated water is substantially longer than would be predicted from the ionic radius of Ra2+ and by analogy with Ba2+, supporting greater water lability in Ra2+ complexes than in their Ba2+ counterparts. Barium often serves as a non-radioactive surrogate for radium, but our findings show that Ra2+ chemistry cannot always be predicted using Ba2+.

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Fig. 1: Structures of the ligand and metal compounds discussed in this work.
Fig. 2: Radiolytic damage of radium crystals with time.
Fig. 3: Conformations of DB30C10 around divalent metal cations.

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Data availability

CCDC depositions 2244265 and 2244266 contain the supplementary crystallographic data for this paper. The crystallographic data for Sm1, Ba2 and Ba3 are also located in the CCDC under depositions 1843893, reference code KEFFIK and reference code PANDUD. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_request@ccdc.cam.ac.uk or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. All data gathered in this manuscript are publicly available through the deposition CIF files.

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Acknowledgements

The staff of the Medical Isotopes Development Group and the Building 3047 Operations Group at Oak Ridge National Laboratory are thanked for their 226Ra production, purification and dispensing efforts. This research was supported by the Laboratory Directed Research and Development (N.A.T.) programme of Oak Ridge National Laboratory. The 226Ra used in this research was supplied by the United States Department of Energy Isotope Program, managed by the Office of Isotope R&D and Production. The manuscript was produced by UT–Battelle, LLC under contract no. DE-AC05-00OR22725 with the United States Department of Energy. The publisher acknowledges the United States Government licence to provide public access under the Department of Energy (DOE) Public Access Plan (https://energy.gov/downloads/doe-public-access-plan). The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript.

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Authors and Affiliations

  1. Radioisotope Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

    Frankie D. White & Samantha K. Cary

  2. Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

    Nikki A. Thiele & Megan E. Simms

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Contributions

F.D.W. constructed and executed the preparation, synthesis, imaging and characterization of Ra/Ba complexes. N.A.T. developed the concept of Ra scXRD and acquired and prepared the stock solution of 226Ra. S.K.C. aided in crystal manipulations for scXRD and 226Ra imaging experiments. M.E.S. aided in preparing the radiological hood for 226Ra work, prepping the 226Ra stock solution and setting up the 226Ra reaction.

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Correspondence to Frankie D. White or Nikki A. Thiele.

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Nature Chemistry thanks Rebecca Abergel, Caterina Ramogida and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1 and 2, Tables 1 and 2 and discussion of CIF B-alerts.

Supplementary Data 1

ScXRD structure of Ba1.

Supplementary Data 2

ScXRD structure of Ra1.

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White, F.D., Thiele, N.A., Simms, M.E. et al. Structure and bonding of a radium coordination compound in the solid state. Nat. Chem. 16, 168–172 (2024). https://doi.org/10.1038/s41557-023-01366-z

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