Metal ion-induced alloying and size transformation of water-soluble metal nanoclusters

Developing novel synthetic strategies of water-soluble alloy NCs and investigating their alloying mechanisms are highly desirable. Herein we report the design of a metal ions-induced alloying strategy for the synthesis of atomically precise water-soluble alloy NCs. By using Au₁₅(GSH)₁₃ NCs as model seeds (here GSH denotes glutathione), Ag(I) ions could trigger the transformation into Au_18-xAg_x(GSH)₁₄ NCs, and then Au(III) ions could be employed to process the composition-polydisperse Au_18-xAg_x(GSH)₁₄ NCs into composition-fixed alloy Au₂₆Ag(GSH)₁₇Cl₂ NCs. By monitoring the alloying process, it is found that the formation of Au_18-xAg_x(GSH)₁₄ NCs experiences two electron-hopping growth [2e^- Au₁₅→ 2e^- (AuAg)_15-17 → 4e^- (AuAg)_18-19 → 4e^- (AuAg)₁₈], while the transformation from (AuAg)₁₈ to Au₂₆Ag mainly involves the formation of intermediate species Au₂₆(GSH)₁₇Cl_n (n = 0-2). Moreover, the position of the single Ag atom in Au₂₆Ag NCs is identified on the NC's surface. The novelty of this study is not only reflected in providing a novel strategy for the synthesis of water-soluble alloy NCs, but also embodied in deepening the fundamental understandings on the alloying mechanism of metal NCs.