Ph.D. topic

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Coordination chemistry of the lanthanides and early actinides in various oxidation states (+III to +V) with N-donor ligands

Boseok Hong

Prof. Dr.Thorsten Stumpf, Dr. Juliane März (HZDR)

Chemistry of the f-elements / Metallorganic actinide chemistry 

02/2021-08/2024

A profound understanding of the coordination chemistry of transuranium elements is essential for reliable safety analyses of potential repositories, but also for efforts in separation of actinides from fission products, and radioecological scenarios such as accidental release or incorporation of actinides. Despite the importance of understanding actinide chemistry, their fundamental properties, especially for the transuranic elements, are not yet fully understood. Covalency, a measure of the sharing of electrons between atoms, is crucial in determining the chemical behavior and mobility of these elements in the environment. Since covalency itself is not a directly observable property, it must be indirectly investigated through other properties – experimental or quantum chemical – influenced by the interaction between the metal orbitals and those of the ligands. In natural systems, several donor functionalities can interact with actinides, and due to this complexity, simplifications are necessary to study the fundamental properties of actinides and transuranium elements on the electronic level.

This PhD research aims to explore the covalency in the coordination chemistry of actinide elements, focusing primarily on the interactions between these elements and nitrogen donor ligands, particularly amidinate ligands (Scheme 1)^1–3. A series of lanthanide (La, Nd, Sm, Eu, Yb, Lu) and actinide (Th, U, Np) complexes in various oxidation states (+III to +V) will be synthesized and characterized in the solid state (using SC-XRD) to gain a comprehensive understanding of the bonding situation between f-block elements and amidinate ligands. Intensive paramagnetic NMR studies will be conducted in solution, applying traditional methods (such as Bleaney⁴ and Reilley^5,6 methods) for separating hyperfine shift (Fermi contact and pseudocontact) contributions to investigate the paramagnetism and covalency of these complexes. Furthermore, quantum chemical calculations will be employed to evaluate the intramolecular bonding situations, trends and electronic structures.

By enhancing the understanding of covalency in actinide elements, this research aims to contribute to safer nuclear waste management strategies and improve predictions of actinide behavior in the environment. The findings could also have broader implications for materials science and the development of new technologies in radiochemistry and related fields.

This PhD project is financially supported by the German Federal Ministry of Education and Research (BMBF) under the project No. 02NUK059B (f-Char).

References

1. Edelmann, F. T. Chapter 3 - Advances in the Coordination Chemistry of Amidinate and Guanidinate Ligands. In Advances in Organometallic Chemistry; Hill, A. F., Fink, M. J., Eds.; Academic Press, 2008; Vol. 57, pp 183–352.
2. Edelmann, F. T. Lanthanide Amidinates and Guanidinates: From Laboratory Curiosities to Efficient Homogeneous Catalysts and Precursors for Rare-Earth Oxide Thin Films. Chem. Soc. Rev. 2009, 38 (8), 2253–2268.
3. Edelmann, F. T. Lanthanide Amidinates and Guanidinates in Catalysis and Materials Science: A Continuing Success Story. Chem. Soc. Rev. 2012, 41 (23), 7657–7672.
4. Bleaney, B. Nuclear Magnetic Resonance Shifts in Solution Due to Lanthanide Ions. J. Magn. Reson. (1969) 1972, 8 (1), 91–100.
5. Reilley, C. N.; Good, B. W.; Allendoerfer, R. D. Separation of Contact and Dipolar Lanthanide Induced Nuclear Magnetic Resonance Shifts: Evaluation and Application of Some Structure Independent Methods. Anal. Chem. 1976, 48 (11), 1446–1458.
6. Di Pietro, S.; Piano, S. L.; Di Bari, L. Pseudocontact Shifts in Lanthanide Complexes with Variable Crystal Field Parameters. Coord. Chem. Rev. 2011, 255 (23), 2810–2820.

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