ACTINIDE BOND properties in gas, liquid and solid state

Project Information

THE ACTINIDE BOND

Grant agreement ID: 101003292

DOI

10.3030/101003292

EC signature date 27 January 2021

Start date 1 February 2021

End date 31 January 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 999 915,00

EU contribution

€ 1 999 915,00

Coordinated by

KARLSRUHER INSTITUT FUER TECHNOLOGIE
Germany

Periodic Reporting for period 3 - THE ACTINIDE BOND (ACTINIDE BOND properties in gas, liquid and solid state)

Reporting period: 2024-02-01 to 2025-07-31

Summary of the context and overall objectives of the project

Understanding the electronic structure and chemical bonding properties of the early actinide (An) elements (Th-Cm) poses a great challenge and frontier in fundamental chemistry and physics. I aim to clarify the link between covalency and strength of the chemical bond of the early An elements from Th to Cm in gas, liquid and solid state materials - combining innovative high challenge experimental setups, advanced synchrotron based spectroscopy methods and state-of-the-art quantum chemical computations. In-situ structural studies of radioactive/radiotoxic gaseous and liquid An materials, combining soft and hard X-ray scattering and absorption methods (RIXS/HR-XANES) to probe An metal centres and their ligands, have not yet been performed at any synchrotron light source in the world. The RIXS and HR-XANES methods probe the occupied and unoccupied parts of the valence band with extraordinary energy resolution and, when combined for the metal and the ligand, unique information on the chemical bond can be obtained. I will gain a deep understanding of the An bond formation mechanisms and will develop spectroscopy methodologies with high potential for a breakthrough in efforts, e.g. to select ligands and An materials with specific characteristics. Ligands and materials with tailored properties are needed for separation of An elements from chemically similar lanthanides or for developing advanced pharmaceutical compounds for targeted cancer treatment. A deep insight into the An electronic structures is also essential for developing innovative spent nuclear fuel matrices and to understand actinide environmental behaviour e.g. in contaminated sites. The new spectroscopy approaches are also expected to boost the advances of quantum chemical theoretical methods. Those are most challenged by the An atoms due to their large number of valence electrons and prevailing influence of relativistic effects in their electronic structure behaviour.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the 'THE ACTINIDE BOND' project, we developed and applied experimental and computational high energy resolution X-ray spectroscopic approaches for an in-depth characterization of bonding properties, specifically bond covalency, of actinide (An) materials in solid, liquid, and gaseous states from both the metal and ligand perspectives. We described the interrelations between An bond covalency and bond stability. Novel in-situ experimental cells and setups were developed and applied.

We published the following manuscripts:

[1] Computational and Spectroscopic Tools for the Detection of Bond Covalency in Pu (IV) Materials
PS Bagus, B Schacherl, T Vitova
(2021) Inorganic chemistry 60 (21), 16090-16102

[2] Relativistic Multiconfigurational Ab Initio Calculation of Uranyl 3d4f Resonant Inelastic X-ray Scattering
R Polly, B Schacherl, J Rothe, T Vitova
(2021) Inorganic chemistry 60 (24), 18764-18776

[3] The mechanism of Fe induced bond stability of uranyl (V)
Tonya Vitova, Radmila Faizova, Jorge I Amaro Estrada, Laurent Maron, Tim Prüßmann, Thomas Neill, Aaron Beck, Bianca Schacherl, Farzaneh Fadaei Tirani, Marinella Mazzanti
(2022) Chemical Science 13, 11038-11047

[4] Implementation of cryogenic tender X-ray HR-XANES spectroscopy at the ACT station of the CAT-ACT beamline at the KIT Light Source
Bianca Schacherl, Tim Prüssmann, Kathy Dardenne, Kirsten Hardock, Volker Krepper, Jörg Rothe, Tonya Vitova, Horst Geckeis
(2022) Journal of Synchrotron Radiation 29 (1), 80-88

[5] Synthesis and characterization of homogeneous (U,Am)O2 and (U,Pu,Am)O2 nanopowders
J.-F. Vigier, D. Freis, O. Walter, O. Dieste Blanco, D. Bouëxière, E. Zuleger, N. Palina, T. Vitova, R. J. M. Konings, K. Popa,
(2022) CrystEngComm 24, 6338-6348

[6] Synthesis, Characterization, and Stability of Two Americium Vanadates, AmVO₃ and AmVO₄
J.-F. Vigier, T. Wiss, N. Palina, T. Vitova, J.-Y. Colle, D. Bouëxière, D. Freis, R. J. M. Konings, K. Popa
(2023) Inorganic Chemistry, 62 (24), 9350–9359

[7] Np(V) Retention at the Illite du Puy Surface
B. Schacherl, C. Joseph, A. Beck, R. Lavrova, A. Schnurr, K. Dardenne, F. Geyer, Z. Cherkezova-Zheleva, J. Göttlicher, H. Geckeis, T. Vitova
(2023) Environmental Science and Technology, 57 (30), 11185–11194

[8] The Electronic Structure of Actinyls: Orbital Properties
P. S. Bagus, C. J. Nelin, K. M. Rosso, B. Schacherl, T. Vitova (2024)
Inorganic Chemistry, 63 (4), 1793-1802

[9] Unveiling Hidden Shake-Up Features in the Uranyl M4‑Edge Spectrum
J. N. Ehrman, K. Shumilov, A. J. Jenkins, J. M. Kasper, T. Vitova, E. R. Batista, P. Yang, X. Li (2024)
JACS Au, 4, 3, 1134–1141

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A brief summary of some of our advances for the reported period follows:

(1) Novel computational quantum chemical approaches were benchmarked together with collaborators for calculations of An M4,5 edge core to core resonant inelastic X-ray scattering (CC-RIXS), valence band-RIXS (VB-RIXS) maps and high energy resolution X-ray absorption near edge structure (HR-XANES) spectra. We understand now in depth how these spectroscopic tools can be useful to obtain advanced understanding for the An-ligand chemical bonding and bond covalency in general and specifically for actinyls (AnO22+) and AnO2. [1, 2] For example, we applied four different theoretical approaches to evaluate the bond covalency in PuO2 valid also for all AnO2. [2]

(2) We clarified the relationship between bond covalency and bond stability when binding Fe(II) to a uranyl(V) (UO21+) molecule by investigating U(IV)-U(VI) organic model molecules with minor modification of the ligand environment. [3] Our results strongly suggest that both covalency and ionicity can lead to stabilization of actinyl(V) – equatorial ligand binding and thus to stable uranyl(V). These insides are of high importance for understanding migration behaviour of U in the environment and the stability of U(V) in environmental conditions incorporated in/sorbed onto minerals containing Fe(II). For the first time we demonstrated the potential of VB-RIXS for characterization of bond covalency for the actinides. This publication is highlighted with an inside front cover of Chemical Science.
We studied the interaction mechanisms of Np with the clay mineral illite and found that the stability of Np(V) sorbed on the surface of the mineral is correlated to decrease of the Np(V)-O axial bond covalency and increase of the interactions with the equatorial ligands. [7] This publication is highlighted with a front cover of Environmental Science and Technology.

(3) The oxidation states and structural properties of (U,Am)O2 and (U,Pu,Am)O2 nanopowders, and their correlations with self-irradiation behavior leading to structure degradation, were investigated. New insights into the stability of Americium (Am) in these cubic materials were obtained. It was shown, for the first time, that Am can oxidize at the surface of nanoparticles and does not change its oxidation state solely as a charge compensation partner of U as previously believed. [5] We also investigated the structural properties and stability of Am vanadates under high alpha irradiation. These ceramics are being explored as potential power sources for space applications such as radioisotope thermoelectric generators, and they must endure extreme conditions, including vacuum, high or low temperatures, and internal irradiation. [6] This publication is highlighted with a front cover of Inorganic Chemistry.

(4) We developed a set-up for An M4,5 edge (3-4 keV) high energy resolution X-ray spectroscopic studies of actinide solid materials at liquid nitrogen temperatures, which allows avoiding radiation damage of chemical bonds for example in metalorganic compounds [4]. It is specifically of high importance for investigating interaction mechanism of actinides in the geosphere leading to their stability and the relation to bonding properties of the actinides.

The mechanism of Fe induced bond stability of uranyl(V)

Np(V) Retention at the Illite du Puy Surface

Synthesis, Characterization, and Stability of Two Americium Vanadates, AmVO₃ and AmVO₄