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 (L 3 -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.