Aromatic character of [Au-13](5+) and [MAu12](4+/6+) (M = Pd, Pt) cores in ligand protected gold nanoclusters - interplay between spherical and planar sigma-aromatics

摘要

The most characteristic feature of planar pi-aromatics is the ability to sustain a long-range shielding cone under a magnetic field oriented in a specific direction. In this article, we showed that similar magnetic responses can be found in sigma-aromatic and spherical aromatic systems. For [Au-13](5+), long-range characteristics of the induced magnetic field in the bare icosahedral core are revealed, which are also found in the ligand protected [Au-25(SH)(18)](-) model, proving its spherical aromatic properties, also supported by the AdNDP analysis. Such properties are given by the 8-ve of the structural core satisfying the Hirsch 2(N + 1)(2) rule, which is also found in the isoelectronic [M@Au-12](4+) core, a part of the [MAu24(SR)(18)](2-) (M = Pd, Pt) cluster. This contrasts with the [M@Au-12](6+) core in [MAu24(SR)(18)](0) (M = Pd, Pt), representing 6-ve superatoms, which exhibit characteristics of planar sigma-aromatics. Our results support the spherical aromatic character of stable superatoms, whereas the 6-ve intermediate electron counts satisfy the 4N + 2 rule (applicable for both pi- and sigma-aromatics), showing the reversable and controlled interplay between 3D spherical and 2D sigma-aromatic clusters.