Supramolecular Host-Guest Inclusion for Distinguishing Cucurbit[7]uril-Based Pseudorotaxanes from Small-Molecule Ligands in Coordination Assembly with a Uranyl Center.

Although the capability of supramolecular pseudorotaxane/rotaxane systems as ligands for coordination with actinides has been identified by the on-going emerging of uranyl-organic polyrotaxane compounds, it is, however, still unknown how supramolecular inclusion affects the coordination assembly of the simple "axle" ligand with uranyl species. Herein, a semi-rigid organic dicarboxylate compound [BzBPCEt]Br2 (L1 ) is selected as a small-molecule "axle" ligand and the corresponding cucurbit[7]uril (CB7)-based [2]pseudorotaxane ligand, [BzBPCEt]Br2 @CB7 (L1 @CB7) has been also synthesized through CB7-based inclusion in this work. A detailed comparison between uranyl complexes from the "axle" ligand L1 and those from pseudorotaxane L1 @CB7 has been conducted, demonstrating the significant role of CB7-based inclusion in distinguishing supramolecular pseudorotaxane ligands from small-molecule dicarboxylates in uranyl coordination assembly. Notably, the impact of supramolecular inclusion on the "axle" linker in the system with cucurbituril macrocycles involved is established for the first time. Detailed structure decipherment suggests that the significant effect of CB7 is attributed to hydrothermal stabilization of the "axle" ligand or increased steric hindrance to the groups nearby originated from the bulky size of macrocyclic CB7.