Cobalt bis(dicarbollide) ions functionalized by CMPO-like groups attached to boron by short bonds; efficient extraction agents for separation of trivalent f-block elements from highly acidic nuclear waste

New boron substituted cobalta bis(dicarbollide)(1-) ion (1) derivatives of formula [(8,8′-(RPhP(O)(CH2)nC(O)N) < (1,2-C2B9H10)2-3,3′-Co]− (R = Ph or C8H17, n = 1, 3a, 3b; R = Ph, n = 2, 3c), [(8-(Ph2P(O)CH2C(O)NR)(1,2-C2B9H10))(1′,2′-C2B9H11)-3,3′-Co]− (R = H, C2H5, CH2C6H5, 5a–c) and [(8-(2RPhP(O)CH2C(O)N(1R)CH2-1,2-C2B9H10))(8′-CH3O-1′,2′-C2B9H10)-3,3′-Co]− (1R = Benzyl, 2R = Ph or C8H17, 7a,b) were prepared with the aim to develop a new class of efficient extraction agents for partitioning of polyvalent f-block elements, i.e. lanthanides and actinides from high-level activity nuclear waste. The anionic ligands were characterized by multinuclear NMR spectroscopy and MS, the structures of Cs3a and the calcium complex of 7a were determined by X-ray diffraction analysis. The crystallographic study of the Cs3a proved a formation of linear chains in the structure, where the metal cation is coordinated by oxygen atoms of the CMPO terminal groups. The X-ray structure of the Ca2+ complex of the ionic ligand 7a proved a 1:3 metal to ligand ratio. Presented also is the X-ray structure of the starting ammonium compound 6 used in the synthesis of 7a and 7b. With exception of 5c, these anionic ligands are of high extraction efficiency, the highest being found for 7a in low polar solvent mixture hexyl methyl ketone–dodecane 1:1. These properties qualify some of these derivatives for possible technological applications.

Three new families of CMPO derivatives of the cobalt(III) bis(1,2-dicarbollide)(1-) ion with short covalent bonds between the function group and boron cage were synthesized starting from corresponding ammonium derivatives. The majority of these anionic ligands are of high efficiency for Ln(III)/An(III) group extraction, the highest in low polar solvent being found for compound containing CMPO group attached via methylene spacer and an auxiliary CH3-O-group present on boron atom of the second dicarbollide sub-cluster. X-ray structure of calcium complex of this ligand is shown in the picture.Figure optionsDownload as PowerPoint slide