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 AcHen3+ (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 (R2 >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.