f-Element coordination and extraction selectivity of a carbamoylmethylphosphine oxide ligand based on a tripodal phosphine oxide scaffold

• A tripodal CMPO ligand has been prepared and characterized.
• Lanthanide- and actinide-ligand complexes have been studied by IR, NMR and in silico.
• This ligand sensitizes the luminescence of Tb3+ and Eu3+ ions in DMSO solutions.
• This ligand extracts Th4+ and UO22+ from 5 M HNO3 with >95% extraction efficiency.
• Modest extraction selectivity is observed for Ce3+ and Pr3+ from 1 M HNO3.

We report here the synthesis and study of a multipodal ligand bearing three CMPO units attached to a trialkylphosphine oxide cap along with the resultant Ln3+, Th4+ and UO22+ metal complexes. This tripodal ligand demonstrates extraction efficiencies of 47% and 44% for the actinide species Th(NO3)4 and UO2(NO3)2 out of 1 M nitric acid into a solution of dichloromethane, while all lanthanide nitrates were extracted with relatively low efficiencies. Further extraction studies utilizing 5 M nitric acid solutions resulted in nearly quantitative actinide extraction. The ability of this ligand to sensitize the metal-centered luminescence of Eu3+ and Tb3+ in DMSO solutions was also investigated. Finally, possible conformations for the structure of the [La(NO3)-ligand]2+ complex were calculated using density functional theory.

A tripodal CMPO ligand has been prepared and characterized by NMR, MS and X-ray crystallography. This ligand’s ability to complex Ln3+ ions as well as Th4+ and UO22+ has been studied in the solid state, in solution, and in silico. This ligand is able to sensitize the luminescence of Tb3+ and Eu3+, and extracts Th(NO3)4 and UO2(NO3)2 out of acidic aqueous solution (5 M HNO3) with greater than 95% extraction efficiency.Figure optionsDownload as PowerPoint slide