U22PO3 and U28PO3 : Chiral Uranium Cage Clusters

Nuclear energy has always been an energy source plagued by negative connotations due to potential dangers of radiation and waste disposal.  Uranium coordination chemistry can provide insight into how “spent” nuclear fuel can be recycled and reused anew in reactors.  Two new uranyl peroxo cage clusters have been synthesized that possess truly unique characteristics.  The two nanoclusters, U22PO3 and U28PO3, are unique in that the structure of the cage cluster is built from four-membered polyhedral belts of uranyl peroxide pentagonal and hexagonal bipyramids.  All other structures previously synthesized were constructed by four-, five-, or six-membered rings of uranyl hexagonal bipyramids.  Furthermore, the two nanoclusters are unique in that they are chiral; the only chiral uranium nanoclusters synthesized to date.  Using small-angle X-ray scattering (SAXS) over time, the formation times and sizes of the nanoclusters could be determined.  It was found that both nanoclusters formed in solution at the same time, however, the crystallization rates were different for each. U22PO3 was found to crystalize first with a period of 14 days and U28PO3 later at around 20 days. This was due to a measured solubility difference between the U22PO3 and the U28PO3 despite very similar structures.  The distribution of cations in the structure is closely related to its solubility, implying that the charge   density is a crucial factor in the creation of strong intracrystal linkages.  It was found that addition of KNO3 increased the rate of crystallization for both  U22PO3 and U28PO3 which reflects the relationship between the cations and solubility of the nanoclusters.  Further study into the synthesis and solubility properties of clusters with different cations, such as rubidium and cesium would be important in further understanding of this solubility difference.

Structure of the U22PO3 nanocluster

Structure of the U28PO3 nanocluster