Organic Functionalization of Uranyl Peroxide Clusters to Impact Solubility

Benzene-1,2-diphosphonic acid (Ppb) was introduced into the uranyl peroxide cluster system, resulting in three Ppb-functionalized uranyl peroxide clusters, (UO₂)₂₀(O₂)₂₀(C₆H₄P₂O₆)₁₀^40- (U₂₀Ppb₁₀), (UO₂)₂₆(O₂)₃₃(C₆H₄P₂O₆)₆^38- (U₂₆Ppb₆), and (UO₂)₂₀(O₂)₂₄(C₆H₄P₂O₆)₆^32- (U₂₀Ppb₆). Dissolution experiments were performed for the potassium salts of U₂₀Ppb₁₀ and U₂₆Ppb₆, which revealed the capacity of U₂₀Ppb₁₀ to dissolve in the organic solvent dimethyl sulfoxide (DMSO). Unlike U₂₀Ppb₁₀, the K salt of U₂₆Ppb₆ did not dissolve in DMSO but was more soluble in water, perhaps due to the lower proportion of Ppb ligands in its structure. In this work, U₂₀Ppb₁₀ and U₂₀Ppb₆ formed as potassium salts and both adopt the fullerene topology of previously reported U₂₀. U₂₀ contains 20 uranyl peroxide units and encapsulates 12 Na cations. It is not possible for unfunctionalized U₂₀ to incorporate 12 K cations owing to space constraints, as is the case in the new clusters reported here. Transformation of U₂₀Ppb₁₀ in water over time to produce U₂₄ was observed, possibly owing to its ability to incorporate K cations, which have been associated with the formation of U₂₄.