Carboxylic acid stimulated silver shell isomerism in a triple core-shell Ag₈₄ nanocluster

Isomerization is highly important in all aspects of science, yet it is rarely observed in nanoscience. Here, we synthesized a unique triple core-shell Ag₈₄ nanocluster displaying isomerism, which is controlled by different carboxylic acids and a one-way transformation (SD/Ag84a → SD/Ag84b). The innermost core is a rare Ag₁₀ nanocluster which comprises an Ag₆ octahedral unit as seen in face-centred cubic (fcc) silver metal and four capped Ag atoms. It templates two crescent-shaped polyoxometalate (W₇O₂₆)^10- shells which are then enclosed in a shell of silver shaped as rugby balls. The organic ligands (ⁱPrS^-, PrCOO^- and PhCOO^-) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of PrCOO^- and PhCOO^-, SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over PrCOOH whereby crystals of SD/Ag84b were isolated if PhCOOH is added during the synthesis of SD/Ag84a. This demonstrates that PhCOOH not only alters the organic coats but also induces metal shell re-organization. This work reveals carboxylate-controlled skeletal isomerism in silver nanoclusters for the first time, thus deepening the understanding of silver nanocluster assembly, flexibility and reactivity.