In Situ Reduction from Uranyl Ion into a Tetravalent Uranium Trimer and Hexamer Featuring Ion-Exchange Properties and the Alexandrite Effect

By utilizing zinc amalgam as an in situ reductant and pH regulator, mild hydrothermal reaction between UO2(CH3COO)(2)center dot 2H(2)O, H2SO4, and Cs2CO3 or between UO2(CH3COO)(2)center dot 2H(2)O, C2H4(SO3H)(2), and K2CO3 yielded a novel cesium U-IV sulfate trimer Cs-4[U3O(SO4)(7)]center dot 2.2H(2)O (1) and a new potassium U-IV disulfonic hexamer K[U6O4(OH)(5)(H2O)(5)][C2H4(SO3)(2)](6)center dot 6H(2)O (2), respectively. Compound 1 features a lamellar structure with a honeycomb lattice, and it represents an unprecedented trimeric U-IV cluster composed of purely inorganic moieties. Complex 2 is built from hexanuclear U4+ cores and K+ ions interconnected by mu(s)-[C2H4(SO3)(2)](2-) groups, leading to the construction of an extended framework rather than commonly observed discrete, neutral molecular sulfonate clusters. The various binding modes of the sulfate and disulfonate groups, especially the multidentate ones, enable additional bridging between metal ions, which promotes oligomerization and isolation of polynuclear species. Furthermore, compound 1 exhibits both ion-exchange properties and the Alexandrite effect, and it is the second example of a uranium complex without chromic functional ligands displaying the latter feature.