An(IV) and An(VI) (An=U & Th for this presentation) have very different aqueous, cluster and solid-state chemistries. An(IV) is poorly soluble in water except at low pH, and forms structures featuring 8-9 coordinate polyhedra. The hexanuclear polycation cluster [An(IV)6(O,OH)8(L)18] (L=ligand) dominates these solutions conditions. U(VI)O2, on the other hand, forms anionic hollow capsules in acidic to alkaline conditions. The uranyl polyhedra are bridged with peroxide and other bidentate and bridging ligands including pyrophosphate and oxalate. Here we present synthesis, solid-state and solution elucidation of cluster, nanocluster and framework materials of An(IV) and An(VI) chemistries in and from aqueous solutions. The uranyl peroxide capsules are ideal for X-ray scattering characterization due to the superior scattering power of uranium (Z=92) and the hollow capsule morphologies. We exploit the high-Z in both X-ray total scattering and small-angle X-ray scattering characterization of different cluster topologies. The combination of these techniques proves diagnostic, even in the absence of a crystal structure. Therefore we further exploit X-ray scattering to predict the topology of a cluster for which we cannot (due to poor crystal quality) obtain single-crystal X-ray data. We also demonstrate the role of the hollow capsule topology in identifying these clusters in solution. We synthesized and structurally characterized endohedral clusters in which Bi-O and Pb-O clusters are enclosed in the uranyl peroxide capsules. These illustrate using capsules to enable dissolution in alkaline pH where solubility and speciation of Bi and Pb is unknown. These clusters also demonstrate the effect of filling the capsule core on the X-ray scattering data. Finally, we present examples of U(IV) and Th(IV) clusters and their conversion to nanoparticles and framework materials. This too is demonstrated by solid-state structure and solution characterization.

Actinide clusters, nanoclusters and cluster-frameworks

253rd National Meeting (2017)

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