Layered Uranyl Hydroxide Assembled from Negatively Charged Host Layers and Interlayer Cations through Noncovalent Interactions

Abstract Uranyl oxide hydroxide phases have attracted sustained attention due to their critical role in the disposal and remediation of radioactive waste. The variety of layered uranyl hydroxides (LUHs) remains limited; only four neutral LUH phases have been structurally confirmed. Herein, we report the synthesis and characterization of the first charged LUH, [BMIM]2[(UO2)5(OH)12(H2O)2] (BMIM-UOH), which represents the fifth confirmed LUH phase. In BMIM-UOH, pentagonal-bipyramidal uranyl units are interconnected to vertex-sharing [(UO2)5(μ2-OH)12] ({U5}) clusters, which further link to form extended two-dimensional anionic sheets, with ionic liquid cations serving as interlayer counterions. The resulting uranyl hydroxide layer exhibits a new anion topology that has not been observed in other uranyl compounds. Notably, the ionic liquid cations occupy the interlayer galleries, where they stabilize the layered structures through electrostatic interactions and hydrogen bonding. This structure represents a rare example of LUHs, highlighting the role of ionic liquids in modulating actinyl hydrolysis and assembling layered materials.