Structure determination of a metastable Au22(SAdm)16 nanocluster and its spontaneous transformation into Au21(SAdm)15

Abstract

It is of great interest to investigate the evolution pattern of gold nanoclusters (Au NCs) due to its significance in understanding the growth mechanism and origin of Au NCs. Capture of metastable cluster intermediates is an effective way to meet this demand since they provide valuable information for understanding the conversion pathway of Au NCs. However, it is still challenging to obtain metastable Au NCs, especially thiol-protected Au NCs, and solve their structures. In this work, a metastable thiol-protected gold nanocluster, Au₂₂(SAdm)₁₆ (Au₂₂), was synthesized and its structure was determined by single crystal X-ray diffraction. Au₂₂ shows a close structure-evolution correlation with Au₂₁(SAdm)₁₅ (Au₂₁). The symmetric Au₁₀ kernel of Au₂₁ is twisted by the insertion of an additional Au-SR unit on the motif during its structure evolution into Au₂₂. The distortion in structures results in significantly distinguishing absorption and emission spectra between Au₂₂ and Au₂₁. Noteworthily, the structure correlation between Au₂₂ and Au₂₁ was also found experimentally that Au₂₂ can spontaneously transform into Au₂₁ due to the metastability of Au₂₂ in solution. This size conversion process was monitored by time-dependent UV-vis spectroscopy and ESI-MS. Furthermore, the solvent effect on the size conversion process was also investigated. This transformation from Au₂₂ to Au₂₁ provides a unique platform for studies on the evolution pattern of gold nanoclusters at the single atom level.