The Propensity of Uranium-Peroxide Systems to Preserve Nanosized Assemblies

Understanding the stability fields and decomposition products of various metal- and actinide-oxide nanoclusters is essential for their development into useful materials for industrial processes. Herein, we explore the spontaneous transformation of the sulfate-centered, phosphate functionalized uranyl peroxide nanocluster {U₂₀P₆} to {U₂₄} under aqueous ambient conditions using time-resolved small-angle X-ray scattering, Raman, and ³¹P NMR spectroscopy. We show that the unusual μ-η¹:η² bridging mode of peroxide between uranyl ions observed in {U₂₀P₆} may lead to its rapid breakdown in solution as evidenced by liberation of phosphate groups that were originally present as an integral part of its cage structure. Remarkably, the uranyl peroxide moieties present after degradation of {U₂₀P₆} undergo cation-mediated reassembly into the {U₂₄} cluster, demonstrating the propensity of the uranyl peroxide systems to preserve well-defined macro-anions.