Carboxylic acid stimulated silver shell isomerism in a triple core–shell Ag(84) 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 Ag(84) 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 Ag(10) nanocluster which comprises an Ag(6) octahedral unit as seen in face-centred cubic (fcc) silver metal and four capped Ag atoms. It templates two crescent-shaped polyoxometalate (W(7)O(26))(10–) shells which are then enclosed in a shell of silver shaped as rugby balls. The organic ligands ((i)PrS(–), (n)PrCOO(–) and PhCOO(–)) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of (n)PrCOO(–) and PhCOO(–), SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over (n)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.