Anionic alkyl diglycoldiamides with covalently bonded cobalt bis(dicarbollide)(1−) ions for lanthanide and actinide extractions

Ionic diamides composed of a N,N′-dialkyl diglycolyl complexing group and two cobalt bis(dicarbollide)(1−) anions 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 [{(N,N-(8-CH2–CH2O)2-1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co)(N′,N′-R)NCOCH2}2O]Na2, where R = n-C4H9, n-C8H17, n-C12H25 and 1-C6H4–4-CH3 (1–4), were prepared and characterized by combination of 11B 1H, 13C NMR spectroscopy, ESI-MS, HPLC and other techniques. Effects of different nitrogen substitution in the structures of 1–4 on the extraction properties were tested. The study resulted in the observation that the compounds are significantly (2–3 orders in magnitude) more efficient extractants for Eu(III) and Am(III) than synergic mixtures of organic N,N′-tetra n-octyl diglycolic acid diamide (TODGA) and chlorinated cobalt bis(dicarbollide) at the same concentrations of both groups. Low polar mixtures of n-dodecane (D) and hexyl methyl ketone (HMK) can be applied as an auxiliary solvent for extraction, replacing thus the polar and less environmentally friendly nitro-, fluoro- and chloro- solvents used in the current dicarbollide liquid–liquid extraction process.