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 AcHe17 3+, ThHe17 4+ and PaHe17 4+ are all found to be true geometric minima, with the He atoms clearly located in the first shell around the actinide. Analysis of AcHen 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 (R2 > 0.95) are found between QTAIM metrics (bond critical point electron densities and delocalisation indices) and the average Ac–He distances, and also with the incremental He binding energies.