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 (UO(2)(2+)) from mixed-metal alkali (Cs(+)), lanthanide (Nd(3+), Sm(3+)), and actinide (Th(4+), UO(2)(2+)) aqueous solutions to an organic, 1,2-dichloroethane (DCE), phase using the ortho-substituted nido-carborane anion, [1,2-(Ph(2)PO)(2)-1,2-C(2)B(10)H(10)](2−) ((PO)Cb(2−)). The reduced (PO)Cb(2−) is generated by electrochemical reduction of the closo-carborane, (PO)Cb, prior to mixing with the aqueous mixed-metal solution. Subsequent UO(2)(2+) release from the captured product, [UO(2)((PO)Cb)(2)](2−), was performed by galvanostatic bulk electrolysis of the DCE phase and back-extraction of UO(2)(2+) to a fresh aqueous phase. The selective capture and release of UO(2)(2+) 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((PO)Cb)]](2), [CoCp*(2)](3)[Nd((PO)Cb)(3)], [CoCp*(2)](3)[Sm((PO)Cb)(3)], and [CoCp*(2)](2)[Th((PO)Cb)(3)].