Insight into Hydrogen Bonding of Uranyl Hydroxide Layers and Capsules by Use of 1H Magic-Angle Spinning NMR Spectroscopy

Solid-state H-1 magic-angle spinning (MAS) NMR was used to investigate local proton environments in anhydrous [UO2(OH)(2)] (alpha-UOH) and hydrated uranyl hydroxide [(UO2)(4)O(OH)(6)center dot 5H(2)O (metaschoepite). For the metaschoepite material, proton resonances of the mu(2)-OH hydroxyl and interlayer waters were resolved, with two-dimensional (2D) double-quantum (DQ) H-1-H-1 NMR correlation experiments revealing strong dipolar interactions between these different proton species. The experimental NMR results were combined with first-principles CASTEP GIPAW (gauge including projector-augmented wave) chemical shift calculations to develop correlations between hydrogen bond strength and observed H-1 NMR chemical shifts. These NMR correlations allowed characterization of local hydrogen-bond environments in uranyl U-24 capsules and of changes in hydrogen bonding that occurred during thermal dehydration of metaschoepite.