Assessing the mechanism of the synergistic action of calixarenes and Co-dicarbollides in lanthanide extractions

The extraction pathway of lanthanide ions from simulated nuclear waste solutions and the synergistic effects of a calixarene and a cobalt dicarbollide anion (CD) have been investigated on a model system by the combined use of electro-spray ionization MS, FTMS ICR, together with 1H and 11B high field NMR spectroscopy techniques. Moreover, the extracting capabilities of the calixarene/BrCD mixture were determined by liquid-liquid extraction tests. An enhanced extraction efficiency of the calixarene/BrCD mixture with respect to the calixarene alone was observed. MS analysis allowed the assessment of a supramolecular ternary association, while the NMR data gave information on the calixarene binding sites for lanthanide ions. Herein, we report the experimental evidence of the formation of a ternary lanthanide/calixarene/Co-dicarbollide aggregate, which allowed us for the first time to assess the mechanism of the synergistic action of calixarenes and CD anions in lanthanide ion extraction. (authors)