Synthesis, structural characterization and transformation of an eight-electron superatomic alloy, [Au@Ag19{S2P(OPr)2}12]

Abstract

Controlling the metal nanoclusters with atomic precision is highly difficult and further studies on their transformation reactions are even more challenging. Herein we report the controlled formation of a silver alloy nanocluster [AuAg₁₉{S₂P(OⁿPr)₂}₁₂] (1) from an Ag₂₀ template via a galvanic exchange route. X-ray structural analysis reveals that the alloy structure comprises of a gold-centered Ag₁₂ icosahedron, Au@Ag₁₂, capped by seven silver atoms. Interestingly upon reacting with one equiv. of silver(I) salt, (1) can transform into a higher nuclearity nanocluster, [Au@Ag₂₀{S₂P(OⁿPr)₂}₁₂]⁺ (2). The conversion process is studied via ESI mass spectrometry and ³¹P NMR spectroscopy. This kind of size-structural transformation at the single atom level is quite remarkable. Furthermore, the compositions of all the doped nanoclusters (1, 2) were fully characterized with ESI-MS and EDS. The blue shift depicted in the UV-visible and emission spectra of the doped nanoclusters (1, 2) compared with the precursor, Ag₂₀, demonstrates that the doping atoms have significant effects on the electronic structures.