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@Sn 8 ) 2 Ge 2 ] 4– ( 1a ), which features a delocalized bonding framework arising from the connection of two spherical aromatic [Rh@Sn 8 ] units via two unique 6σ-aromatic [GeSn 4 ] 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@Sn 8 ) 2 Ge 2 ] 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.