Potential application of Kläui ligands in actinide separations

We have undertaken a systematic experimental and computational study of the complexation of Cp*Co[P(O)(OR) 2 ] 3 - (Cp* = pentamethylcyclopentadienyl) ligands with f-block metal ions (i.e., lanthanides and actinides). As part of this work, the complexation of La 3+ ion with Cp*Co[P(O)(OR) 2 ] 3 - ligands has been studied as the alkyl group was systematically varied from methyl to n-propyl (R = -CH 3 , -CH 2 CH 3 , and -CH 2 CH 2 CH 3 ). For ligands in which R = -CH 3 or -CH 2 CH 3 , complexes with ligand-to-La stoichiometries of 1:1 and 2:1 were formed. In contrast, only the 1:1 complex was isolated when R = -CH 2 CH 2 CH 3 . Computational modeling indicates that the coordination number for La in the 1:1 and 2:1 complexes is 8 and 9, respectively. A prototypical extraction chromatography resin containing Cp*Co[P(O)(OEt) 2 ] 3 - (1b) has been prepared. The resin consists of 0.75 wt% 1b on Amberlite® XAD-7. This resin strongly sorbs Am 3+ and Pu 4+ . The sorption of these ions decreases with increasing nitric acid concentration, but this effect is more pronounced for Am 3+ . This allows for convenient separation of Am 3+ from Pu 4+ by simple adjustments in the HNO 3 concentration. The tripodal geometry of 1b disfavors the complexation of UO 2 2+ , so sorption of U(VI) by the Ib-containing resin is weak.