Effects of bromine-containing counterion salts in directing the structures of medium-sized silver nanoclusters

The preparation and structural determination of silver nanoclusters (especially the medium-sized Ag clusters) remain more challenging relative to those of their gold counterparts because of the comparative instability of the former. In this work, three medium-sized Ag clusters were controllably synthesized and structurally determined, namely, [Ag₅₂(S-Adm)₃₀Br₄H₂₀]^2- (Ag₅₂ for short), Ag₅₄(S-Adm)₃₀Br₄H₂₀ (Ag₅₄ for short), and [Ag₅₈(S-Adm)₃₀Br₄(NO₃)₂H₂₂]²⁺ (Ag₅₈ for short) nanoclusters. Specifically, the introduction of PPh₄Br gave rise to the generation of Ag₅₂ and Ag₅₄ nanoclusters with homologous compositions and configurations, while the TOABr salt selected Ag₅₈ as the sole cluster product, whose geometric structure was completely different from those of Ag₅₂ and Ag₅₄ nanoclusters. In addition, the optical absorptions and emissions of the three medium-sized silver nanoclusters were compared. The findings in this work not only provide three uniquely medium-sized nanoclusters to enrich the silver cluster family but also point out a new approach (i.e., changing the counterion salt) for the preparation of new nanoclusters with novel structures.