Coordination-Adaptive Polydentate Pseudorotaxane Ligand for Capturing Multiple Uranyl Species

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Uranyl hydrolysis in aqueous environments complicates control over uranyl species for separation and synthesis.
• Existing methods lack precise control due to pH-dependent uranyl speciation.

Purpose of the Study:

• To develop a novel multidentate pseudorotaxane ligand for capturing uranyl species at different pH values.
• To achieve pH-independent uranyl coordination and recognition of various uranyl hydrolysis products.

Main Methods:

• Synthesis of a DPO@CB[7] pseudorotaxane ligand using cucurbit[7]uril (CB[7]) and 4,4'-bipyridine-N,N'-dioxide (DPO).
• Coordination studies with uranyl species across a wide pH range.
• Structural characterization using single-crystal X-ray diffraction.
• Physicochemical characterization of obtained uranyl-rotaxane compounds (URC1-4) via PXRD, IR, TGA, and luminescence.

Main Results:

• A pH-tolerant DPO@CB[7] pseudorotaxane ligand was successfully synthesized and demonstrated effective uranyl capture.
• Four novel uranyl-rotaxane compounds (URC1-4) were obtained, showcasing adaptive coordination to monomeric to tetrameric uranyl species.
• X-ray diffraction revealed four distinct coordination modes of the flexible DPO@CB[7] ligand with uranyl centers.
• Characterization confirmed the high phase purity and physicochemical properties of URC1 and URC2.

Conclusions:

• The DPO@CB[7] pseudorotaxane ligand exhibits remarkable adaptivity and flexibility for recognizing and capturing diverse uranyl species.
• This work presents a successful strategy for designing multifunctional supramolecular ligands for actinide separation.
• The findings offer valuable insights for future developments in on-demand separation and tailored synthesis of uranyl compounds.