Selective electrochemical capture and release of uranyl from aqueous alkali, lanthanide, and actinide mixtures using redox-switchable carboranes

We report the selective electrochemical biphasic capture of the uranyl cation (UO22+) from mixed-metal alkali (Cs+), lanthanide (Nd3+, Sm3+), and actinide (Th4+, UO22+) aqueous solutions to an organic, 1,2-dichloroethane (DCE), phase using the ortho-substituted nido-carborane anion, [1,2-(Ph2PO)(2)-1,2-C2B10H10](2-) (Cb-PO(2-)). The reduced Cb-PO(2-) is generated by electrochemical reduction of the closo-carborane, Cb-PO, prior to mixing with the aqueous mixed-metal solution. Subsequent UO22+ release from the captured product, [UO2(Cb-PO)(2)](2-), was performed by galvanostatic bulk electrolysis of the DCE phase and back-extraction of UO22+ to a fresh aqueous phase. The selective capture and release of UO22+ was confirmed by combined ICP-OES and NMR spectral analyses of the aqueous and organic phases, respectively, against the newly synthesized nido-carborane complexes, [[CoCp*(2)][Cs(Cb-PO)]](2), [CoCp*(2)](3)[Nd(Cb-PO)(3)], [CoCp*(2)](3)[Sm(Cb-PO)(3)], and [CoCp*(2)](2)[Th(Cb-PO)(3)].