Dynamic Phosphonic Bridges in Aqueous Uranyl Clusters

Cation‐Directed Isomerization of the U28 Uranyl‐Peroxide Cluster

“…This preference was resolved using a closely related cluster, the [(UO 2 ) 22 (O 2 ) 15 (PHO 3 ) 20 ‐(H 2 O) 10 ] 26– ( U 22 ), which utilizes potassium salts in the synthesis, but crystallizes with no K + cations inside the cage (Figure D) . All protons on the µ 3 ‐PHO 3 bridges of the U 22 point into the cluster, and the lone pairs point outwards, toward the bulk solvent . Only conformer A I exists in freshly crystallized U 22 .…”

“…In order to detect such subtle changes, we exploited the covalent character of the hydrogen–phosphorus bond in the phosphonic bridges (µ 3 ‐PHO 3 ) of one variety of these cage clusters. In this way, we could use complementary 1 H and 31 P NMR analyses , . The [(UO 2 ) 28 (O 2 ) 20 (PHO 3 ) 24 (H 2 O) 12 ] 32– , U 28 (Figure ), cluster was examined in both the solid state and in solution, where two sets of structural conformational isomers, with hydrogen atoms facing both inward and outward, were identified for each µ 3 ‐PHO 3 bridge via single crystal X‐ray diffraction, 31 P, and 1 H NMR spectroscopy , .…”

“…In this way, we could use complementary 1 H and 31 P NMR analyses , . The [(UO 2 ) 28 (O 2 ) 20 (PHO 3 ) 24 (H 2 O) 12 ] 32– , U 28 (Figure ), cluster was examined in both the solid state and in solution, where two sets of structural conformational isomers, with hydrogen atoms facing both inward and outward, were identified for each µ 3 ‐PHO 3 bridge via single crystal X‐ray diffraction, 31 P, and 1 H NMR spectroscopy , . These two isomers are identified with red (inward‐facing) and blue (outward‐facing) in the top of Figure and cannot interconvert.…”

“…Each of the inward‐ and outward‐facing µ 3 ‐PHO 3 bridge (super)sets is fixed, but can assume four additional orientation subsets depending on the position of the lone pairs of electrons on adjacent bridging oxygens relative to the hydrogen atom (Figure A–D). These conformers were identifiable in solution by careful examination of variable temperature 1 H and 31 P NMR spectra …”

“…Thus, for example, conformer A can exist with either an overall inward ( A I ) or overall outward ( A O ) orientation. Minute changes in the solution structure of this U 28 cluster can be examined by identifying which µ 3 ‐PHO 3 bridge conformers ( A I/O – D I/O ) relate to each 1 H NMR signal that was previously assigned to the massive cluster using 1 H DOSY NMR at room temperature . In this manuscript, we propose proton signal assignment and investigate the structural effects caused by the introduction of various potential guest counter‐cations.…”