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.     

Seventeen‐Coordinate Actinide Helium Complexes

The geometries and electronic structures of molecular ions featuring He atoms complexed to actinide cations are explored computationally using density functional and coupled cluster theories. A new record coordination number is established, as AcHe₁₇³⁺, ThHe₁₇⁴⁺, and PaHe₁₇⁴⁺ are all found to be true geometric minima, with the He atoms clearly located in the first shell around the actinide. Analysis of AcHe_n ³⁺ (n =1–17) using the quantum theory of atoms in molecules (QTAIM) confirms these systems as having closed shell, charge‐induced dipole bonding. Excellent correlations (R ²>0.95) are found between QTAIM metrics (bond critical point electron densities and delocalization indices) and the average Ac−He distances, and also with the incremental He binding energies.