[Co3@Ge6Sn18]5-: A Giant σ-Aromatic Cluster Analogous to H3+ and Li3+

Abstract

Aromaticity is one of the most important concepts in chemistry and has been successfully extended to all-metal clusters. However, the study of all-metallic aromatic clusters remains in its early stages, with σ-aromatic clusters mostly limited to small sizes (≤12) that often require external stabilization. In this work, we report the first Ge/Sn-based trimer, [Co3@Ge6Sn18]5-, which can be rationalized as the fusion of three [Co-@Ge3Sn64-] units via a Ge3 face. Theoretical studies have revealed that two σ-electrons are delocalized across the entire trimer, with the spherical aromaticity of each [Co@Ge3Sn6] unit and the global σ-aromaticity of [Co3@Ge6Sn18]5- further supported by its electron delocalization and magnetic behavior. As a result, this trimer can be viewed as a giant σ-aromatic counterpart to triatomic H3+ and Li3+. Our findings suggest the potential for synthesizing cluster-of-cluster analogs of discrete all-metallic aromatic species, such as Al42-, and further enhance our understanding of chemical bonding.