Electronic Structure of Uranyl Complexes probed by Valence and X-Ray Spectroscopy

This presentation will showcase the capabilities of relativistic quantum chemistry approaches in exploring the electronic structure of actinide-containing compounds. The focus will be on luminescence properties and core-level spectroscopic observables of the uranyl moiety (UO22+) within both linear and bent uranyl complexes. Given the challenges associated with nuclear waste management and the environmental impact of fission products, efficient extraction and characterization methods for actinide-containing compounds are of great societal importance.<br/><br/>The electronic structure of actinide compounds remains poorly understood compared to other elements in the periodic table. Valence- and core-level spectroscopic techniques offer valuable insights into this complex subject. The presentation will demonstrate how luminescence spectroscopy and X-ray spectroscopies serve as sensitive tools for probing the electronic structure and bonding nature between the uranyl moiety and its coordinated ligands.<br/><br/>Specifically, the talk will cover the application of relativistic Time-Dependent Density Functional Theory (TDDFT) with the CAM-B3LYP functional. This method has proven effective in providing accurate excitation/emission energies and vibronic progressions for linear uranyl complexes (UO₂Cl₄^2-, UO₂F₅^3-, UO₂(CO₃)₃^4-, UO₂(NO₃)L₂), enabling the assignment of experimental data [1]. Additionally, the impact of bending the uranyl moiety on spectroscopy and observed vibronic progressions will be discussed [2].<br/><br/>The presentation will also delve into TD-DFT simulations of the core spectra of the uranyl tetrachloride dianion (UO₂Cl₄^2-) in the Cs₂UO₂Cl₄ crystal. These simulations align with previously reported angle-resolved near-edge X-ray absorption spectroscopy (NEXAFS) at the oxygen K-edge and high-energy resolution fluorescence detected (HERFD-XANES) at the uranium M₄- and L₃-edges [3].<br/><br/>[1] H. Oher et al. <i>Inorg. Chem.</i> <b>2020</b>, <i>59</i> 5896; H. Oher et al. <i>Inorg. Chem.</i> <b>2020</b>, <i>59</i>, 15036; H. Oher et al. <i>Inorg. Chem.</i> <b>2022</b>, <i>61</i>, 890.<br/>[2] H. Oher et al. Inorg. Chem. <b>2023</b>, <i>62</i>, 9273–9284.<br/>[3] W. A. Misael, A. S. P. Gomes, <i>Inorg. Chem.</i> <b>2023</b>, <i>62</i>, 11589–11601.