Sulfate-Centered Sodium-Icosahedron-Templated Uranyl Peroxide Phosphate Cages with Uranyl Bridged by μ–η¹:η² Peroxide

Two novel hybrid uranyl peroxide phosphate cage clusters, designated U₂₀P₆ and U₂₀P₁₂, contain peroxide bridges between uranyl in an unusual μ–η¹:η² configuration, as well as the common μ–η²:η² configuration. These appear to be the only high-nuclearity metal peroxide complexes containing μ–η¹:η² peroxide bridges, and they are unique among uranyl peroxide cages. Both clusters contain 20 uranyl polyhedra, and U₂₀P₆ and U₂₀P₁₂ contain 6 and 12 phosphate tetrahedra, respectively. The 20 uranyl polyhedra in both cages are arranged on the vertices of distorted topological dodecahedrons (20 vertex fullerenes). Each cage is completed by phosphate tetrahedra and is templated by a sulfate-centered Na₁₂ cluster with the Na cations defining a regular convex isocahedron. Whereas μ–η²:η² peroxides are essential features of uranyl peroxide cages, where they form equatorial edges of uranyl hexagonal bipyramids, the μ–η¹:η² peroxide groups in U₂₀P₆ and U₂₀P₁₂ are associated with strong distortions of the uranyl polyhedra. Formation of U₂₀P₆ and U₂₀P₁₂ is a further demonstration of the pliable nature of uranyl polyhedra, which contributes to the tremendous topological variability of uranyl compounds. Despite the unusual structure and highly distorted polyhedral geometries of U₂₀P₆, small-angle X-ray scattering and Raman spectra suggest its stability in the aqueous solution and solid state.