Tetrahedral Au₁₇⁺: A Superatomic Molecule with a Au₁₃ FCC Core

A unique tetrahedral structure of Au₁₇⁺ (<i>T</i>_d) is found by using first-principles global optimization, which lies 0.40 eV lower in energy than the previously known structure and has a fairly large HOMO–LUMO gap (1.46 eV) at the TPSS/def2-TZVP level. For neutral Au₁₇, this tetrahedral structure is distorted to <i>D</i>_2d symmetry but is also 0.18 eV lower in energy than the previous flat cage structure. Au₁₇⁺ (<i>T</i>_d) has a FCC Au₁₃ octahedral core, and the other four gold atoms are above its four triangular faces. Magic electronic stability of the cluster is explained by the super valence bond model, of which it can be seen as a superatomic molecule in the electronic structure. Moreover, the cluster can also be viewed as a network of eight 2e-superatoms. This Au₁₇⁺ cluster mimics the behavior of the Au₂₀ pyramid, known as a unique one among the family of gold clusters since its discovery in 2003, in electronic structures