Core-Excited States of Linear and Bent Uranyl Complexes: Insights from High-Energy Resolution X-ray Spectroscopy and Relativistic Quantum Chemistry
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 with those of other uranyl complexes reported in the literature. This evaluation is complemented by 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 two-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…
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