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)2·2H2O, H2SO4, and Cs2CO3 or between UO2(CH3COO)2·2H2O, C2H4(SO3H)2, and K2CO3 yielded a novel cesium UIV sulfate trimer Cs4[U3O(SO4)7]·2.2H2O (1) and a new potassium UIV disulfonic hexamer K[U6O4(OH)5(H2O)5][C2H4(SO3)2]6·6H2O (2), respectively. Compound 1 features a lamellar structure with a honeycomb lattice, and it represents an unprecedented trimeric UIV cluster composed of purely inorganic moieties. Complex 2 is built from hexanuclear U4+ cores and K+ ions interconnected by μ5-[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.