Lanthanide and actinide extractions with anionic ligands based on cobalt bis(dicarbollide) ions with covalently bonded CMPO functions

Compounds were synthesized with the aim to develop efficient extraction agents for liquid-liquid extraction of polyvalent cations, i.e. lanthanides and actinides from high-level activity nuclear waste. Compounds of general formulation [(8-CMPO-(CH₂-CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]^- with different phosphorus and nitrogen substitution (CMPO=²R,³R P(O)-(CH₂)_nC(O)N¹R, ¹R=t-octyl, H, Ph, ²R=Ph, n-octyl, ³R=Ph, n=1,2)-(4a to 4e), were prepared and characterized by combination of ¹¹B NMR, ¹H high field NMR, ESI-M.S., HPLC and other techniques. Molecular structure of the sodium complex of ligand 4a (¹R=t-octyl, ²R=³R=Ph, n=1) was determined by single crystal X-ray diffraction analysis. Effect of several modifications in the structure of 4a–4e on the extraction properties was outlined. The study resulted in the definition of ionic ligand with enhanced extraction efficiency for 4a,b (t-octyl and H on the amidic nitrogen atom) and a better solubility of 4a and 4d (¹R=t-octyl, ²R=n-Oct, ³R=Ph, n=1) in less polar solvents. Low polar mixtures of hydrogenated tetrapropylene (TPH) hexyl methyl ketone (HMK) can be applied as an auxiliary solvent for 4a, selected for detailed studies, replacing thus the polar and less environmentally friendly nitro-, fluoro- and chloro- solvents used in the current dicarbollide liquid-liquid extraction process. Results of the fission products separation from the simulated PUREX feed using 4a are presented inclusive procedures for Eu³⁺ stripping.