Structural Snapshots of Cluster Growth from {U6} to {U38} During the Hydrolysis of UCl4

Herein we report the assembly of large uranium(IV) clusters with novel nuclearities and/or shapes from the controlled hydrolysis of UCl4 in organic solution and in the presence of the benzoate ligands. {U6}, {U13}, {U16}, {U24}, {U38} oxo and oxo/hydroxo clusters were isolated and crystallographically characterized. These structural snapshots indicate that larger clusters are slowly built from the condensation of octahedral {U6} building blocks. The uranium/benzoate ligand ratio, the reaction temperature and the presence of base play an important role in determining the structure of the final assembly. Moreover, the isolation of different size cluster {U6} (few hours), {U16} (3 days), {U24} (21 days) from the same solution in a chosen set of conditions shows that the assembly of uranium oxo clusters in hydrolytic conditions is time dependent. Growing on U: Large UIV clusters slowly assemble in organic solution, upon controlled hydrolysis of UCl4, from a hexanuclear {U6} cluster. The process is time dependent and is affected by temperature and added base.