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−, nPrCOO− and PhCOO−) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of nPrCOO− and PhCOO−, SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over nPrCOOH 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.