Canonical Zn-Zn pseudo-triple bond with double aromaticity in D_5h-Zn₂Na₅^- cluster

In transition metals, the formation of intermetallic multiple bonds typically depends on d-orbital coupling. However, zinc, with its fully occupied 3d electron shell, struggles to form multiple bonds via this pathway, rendering Zn-Zn triple bonds exceptionally rare. Here, we propose, in theory, an all-metal global-minimum anion cluster, D_5h-Zn₂Na₅^-. D_5h-Zn₂Na₅^- exhibits a pseudo yet canonical Zn-Zn triple bond with pronounced electron delocalization as well as dual aromaticity, including cubic aromaticity across the entire skeleton, and σ aromaticity only belongs to the pentagonal and equatorial Na₅^- ligand framework. This unique Zn₂ bonding motif and electronic structure emerge in the absence of axial ligand coordination, representing a rare example of dual aromaticity in an all-metal system. Bonding analysis reveals that this novel bonding model comprises two orthogonal delocalized π bonds formed through partial electron transfer from the equatorial Na ligands to Zn 4p orbitals, along with a delocalized quasi-σ bond with a little Zn-Zn interaction. Furthermore, comparative studies reveal that the σ-aromaticity of the planar Na₅^- ring ligands is more potent than that of the planar Li₅^- ring, which dominates the D_5h geometry of Zn₂Na₅^-, whereas Zn₂Li₅^- adopts a sliding triple bond configuration, whose stability relies on a mixed coordination mode involving both planar and axial lithium atoms. This discovery establishes the strategic design of ligand frameworks as a promising paradigm for stabilizing unconventional multiple bonds and engineering specific aromaticity in multi-metallic clusters.