σ-Aromatic Ge–Sn Bridges in a Triply-Bonded Bare Cluster Dimer with a Long-Lived Triplet State

Constructing extended cluster aggregates requires a deeper understanding of strategies for connecting structural motifs. Herein, we report the synthesis and structural elucidation of the triply bonded dimeric cluster [(Rh@Sn₈)₂Ge₂]^4- (<b>1a</b>), which features a delocalized bonding framework arising from the connection of two spherical aromatic [Rh@Sn₈] units via two unique 6σ-aromatic [GeSn₄] bridges. The resulting framework simultaneously exhibits global aromaticity and multiple localized aromatic fragments, highlighting a rational route toward controlled cluster growth and offering new synthetic avenues for cluster-based bulk materials. Moreover, femtosecond-to-nanosecond transient absorption spectroscopy revealed an exceptionally long-lived triplet excited state (τ_av = 178 μs) for [(Rh@Sn₈)₂Ge₂]^4-, significantly longer than those reported for metal nanoclusters in the condensed phase. This finding supplements the limited excited-state features of bare metal nanoclusters and provides a new strategy for achieving prolonged excited-state lifetimes in cluster systems.