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arXiv · 2504.05542

Core-Excited States of Linear and Bent Uranyl Complexes: Insights from High-Energy Resolution X-ray Spectroscopy and Relativistic Quantum Chemistry

Wilken Aldair Misael·Lucia Amidani·Juliane März·Elena F. Bazarkina·Kristina O. Kvashnina·Valérie Vallet·André Severo Pereira Gomes
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Abstract

Advanced X-ray spectroscopic techniques are widely recognized as state-of-the-art tools for probing the electronic structure, bonding, and chemical environments of the heaviest elements in the periodic table. In this study, we employ X-ray absorption near-edge structure measurements in high-energy resolution fluorescence detection (HERFD-XANES) mode to investigate the core states arising from excitations out of the U 3d${_{3/2}}$ (M$_4$ edge) levels for molecular complexes in which the uranyl moiety deviates from linearity to varying degrees, and in particular systems containing the UO$_2$Cl$_2$ group such as UO$_2$Cl$_2$.n(H$_2$O) and UO$_2$Cl$_2$(phen)$_2$, which in the latter case exhibits a pronounced O-U-O bending angle. These U M$_4$ edge HERFD-XANES spectra are compared to those of other uranyl complexes reported in the literature. This evaluation is complemented by \textit{ab initio} relativistic quantum chemistry simulations on the [UO$_2$(NO$_3$)$_2$.n(H$_2$O)], UO$_2$Cl$_2$.n(H$_2$O) and UO$_2$Cl$_2$(phen)$_2$ systems, using 2-component Time-Dependent Density Functional Theory (TD-DFT) with the CAM-B3LYP functional, employing the Tamm-Dancoff approximation (2c-TDA). Our 2c-TDA simulations show modest deviations from the HERFD-XANES data, with peak splittings differing by less than 1 eV from experimental values. These core-excited states were further characterized by Natural Transition Orbital (NTO) analysis. Overall, our results highlight the influence of equatorial ligands on the spectroscopic signatures, particularly pronounced in UO$_2$Cl$_2$(phen)$_2$, where the U 3d$_{3/2}$ $\rightarrow$ 5f$\sigma_u^*$ satellite transition appears at lower energies compared to the other systems studied.

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Wilken Aldair Misael, Lucia Amidani, Juliane März, Elena F. Bazarkina, Kristina O. Kvashnina, Valérie Vallet, André Severo Pereira Gomes. 2025-04-07. Core-Excited States of Linear and Bent Uranyl Complexes: Insights from High-Energy Resolution X-ray Spectroscopy and Relativistic Quantum Chemistry. https://arxiv.org/abs/2504.05542

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