Hierarchy of Pyrophosphate-Functionalized Uranyl Peroxide Nanocluster Synthesis

Herein,
we report a new salt of a pyrophosphate-functionalized uranyl peroxide
nanocluster {U24Pp12} (1) exhibiting Oh molecular symmetry both in
the solid and solution. Study of the system yielding 1 across a wide range of pH by single-crystal X-ray diffraction, small-angle
X-ray scattering, and a combination of traditional 31P
and diffusion-ordered spectroscopy (DOSY) NMR affords unprecedented
insight into the amphoteric chemistry of this uranyl peroxide system.
Key results include formation of a rare binary {U24}·{U24Pp12} (3) system observed under alkaline
conditions, and evidence of acid-promoted decomposition of {U24Pp12} (1) followed by spatial rearrangement
and condensation of {U4} building blocks into the {U32Pp16} (2) cluster. Furthermore, 31P DOSY NMR measurements performed on saturated solutions
containing crystalline {U32Pp16} show only trace
amounts (∼2% relative abundance) of the intact form of this
cluster, suggesting a complex interconversion of {U24Pp12}, {U32Pp16}, and {U4Pp4–x} ions.