Selective recognition and extraction of the uranyl ion.

A tripodal receptor capable of extracting uranyl ion from aqueous solutions has been developed. At a uranyl concentration of 400 ppm, the developed ligand extracts ∼59% of the uranyl ion into the organic phase. The new receptor features three carboxylates that converge on the uranyl ion through bidentate interactions. Solution studies reveal slow exchange of the carboxylates on the NMR time scale. The crystal structure of the complex shows that the carboxylates coordinate to uranyl ion while the amides hydrogen bond to one of the uranyl oxo-oxygen atoms. The hydrophobic coating of the ligand and its rigidity contribute to its ability to selectively extract uranyl ion from dilute aqueous solutions.