Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems

N-donor ligands such as n-Pr-BTP [2,6-bis­(5,6-di­propyl-1,2,4-triazin-3-yl)­pyridine] preferentially bind trivalent actinides (An$^{3+}$) over trivalent lanthanides (Ln$^{3+}$) in liquid–liquid separation. However, the chemical and physical processes responsible for this selectivity are not yet well understood. Here, an explorative comparative X-ray spectroscopy and computational (L3-edge) study for the An/Ln L$_{3}$-edge and the N K-edge of [An/Ln(n-Pr-BTP) $_{3}$](NO$_{3}$)$_{3}$, [Ln(n-Pr-BTP) $_{3}$](CF$_{3}$SO$_{3}$)$_{3}$ and [Ln(n-Pr-BTP) $_{3}$](ClO$_{4}$)$_{3}$ complexes is presented. High-resolution X-ray absorption near-edge structure (HR-XANES) L$_{3}$-edge data reveal additional features in the pre- and post-edge range of the spectra that are investigated using the quantum chemical codes FEFF and FDMNES. X-ray Raman spectroscopy studies demonstrate the applicability of this novel technique for investigations of liquid samples of partitioning systems at the N K-edge.