Complexation of U(VI) with N-donor ligands studied by high energy resolution X- ray spectroscopy and computations

The degree of involvement of actinide 5f electrons in chemical bonds and trends along the actinide series are still under debate. In recent years, experimental techniques such as high-resolution X-ray absorption near-edge structure (HR-XANES) and valence band resonant inelastic X-ray scattering (VB-RIXS) have been developed. These techniques have made significant contributions to the study of the electronic structure of actinides (An), particularly regarding the covalency of the An-ligand bond. Uranyl(VI) (UO22+) solutions with UO22+ to ligand ratios of 1:10/20 were prepared and investigated to evaluate the influence of the N-donor (SO3-Ph-BTP, iPr-BTP, nPr-BTP) or O-based (TODGA, NO3-) ligands on the electronic structure of UO22+. The local coordination of UO22+ was probed by U L3-edge extended X-ray absorption fine structure (EXAFS) experimental technique. The influence of ligand binding in the equatorial plane on the covalency of the axial uranyl bond was evaluated by U M4 edge HR-XANES. U M4 VB-RIXS was employed to study changes of UO22+-ligands bond covalency. The X-ray spectroscopic experiments were performed at the ACT station at the CAT-ACT beamline and the INE-Beamline at the KIT Light Source, Karlsruhe, Germany. ... mehrWe will illustrate that N-donor ligands bind to UO22+, which leads to small U(VI) electronic structure variations. Calculations predict reduced bond covalency for TODGA compared to BTP ligands, mainly due to the absence of central oxygen atom π interaction in TODGA.