Water-soluble multi-cage super tetrahedral uranyl peroxide phosphate clusters

Combination of uranyl, peroxide, phosphate, and counter ions under ambient conditions in aqueous solution over the pH range 5.5-6.5 results in the self-assembly of a large super tetrahedral cluster containing 124 uranyl hexagonal bipyramids and 32 phosphate tetrahedra designated U ₁₂₄P₃₂. With a diameter of 4 nm, U₁₂₄P ₃₂ consists of four symmetrically identical cage clusters, each built from 23 uranyl hexagonal bipyramids and eight phosphate tetrahedra, as well as a central cage defined by 52 uranyl hexagonal bipyramids and 32 phosphate tetrahedra. It is the first uranyl-based cluster that contains multiple cages and it also has the highest number of uranyl ions. U₁₂₄P₃₂ contains 152 peroxide groups that are bidentate bridges between uranyl ions. Crystals of U₁₂₄P₃₂ provided structural details, and were dissolved for subsequent small-angle X-ray scattering and electrospray ionization mass spectrometry characterization that indicated U ₁₂₄P₃₂ remains intact upon dissolution in water. Whereas uranyl phosphates are generally insoluble in water, prompting interest in their applications in remediating contaminated water, U₁₂₄P₃₂ is highly soluble, reflecting the impact of the nanoscale structure on solubility.