Combination of chlorinated cobalt dicarbollide with N,O-donor ligands in extraction systems for separating f-elements†

Extraction systems for the separation of f-elements are an active area of research and continue to evolve. Modifications are being made to both solvents and extractant structures; however, the variety of available solvents and synthetically accessible ligands remains limited. In this context, the use of synergistic additives presents a promising strategy for enhancing the extraction performance of existing systems. In the present study, we investigated modifications to extraction systems aimed at f-element separation, with a particular focus on diamides of 1,10-phenanthroline-2,9-dicarboxylic acid and 2,2′-dipyridyl-6,6′-dicarboxylic acid in combination with chlorinated cobalt dicarbollide (CCD⁻) in the polar fluorinated organic diluent m-nitrobenzotrifluoride (F-3). The advantages and limitations of the resulting extraction systems were assessed. Special attention was given to changes in complexation mechanisms and to the speciation of actinides and lanthanides within these systems, as studied by UV–vis titration, X-ray diffraction (XRD), radiometric analysis, Raman spectroscopy, and ¹¹B-NMR spectroscopy.