Four self-assembling clusters of uranyl peroxide polyhedra have been formed in alkaline aqueous solutions and structurally characterized. These clusters consist of 28, 30, 36 and 44 uranyl polyhedra and exhibit complex new topologies. Each has a structure that contains topological squares, pentagons and hexagons. Analysis of possible topologies within boundary constraints indicates a tendency for adoption of higher symmetry topologies in these cases. Small angle X-ray scattering data demonstrated that crystals of one of these clusters can be dissolved in ultrapure water and that the clusters remain intact for at least several days.

Uranyl peroxides have been intensively studied recently because they form topologically complex structures including spherical clusters containing tens of uranyl polyhedra. In all uranyl peroxides reported to date, the coordination of U(6+) cations by peroxide is bidentate. The compound K(2)(Mg(H(2)O)(6))(4)[(UO(2))(3)(O(2))(8)].2H(2)O has been synthesized and characterized and contains a trimer of linked uranyl peroxide polyhedra. The central U(6+) cation is linked to two peroxide groups in a mu-eta(2):eta(1) configuration. Inclusion of this mode of linkage could dramatically increase the flexibility and topological complexity of uranyl peroxide nanoscale clusters.

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