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

The development of novel strategies for the synthesis of water-soluble alloy nanoclusters (NCs) and investigations of their alloying mechanisms are highly desirable. Herein, we report the design of a metal ion-induced alloying strategy for the synthesis of atomically precise water-soluble alloy NCs. The transformation of Au₁₅(GSH)₁₃ NCs as model seeds (here GSH denotes water-soluble glutathione) into Au_18−xAg_x(GSH)₁₄ NCs was triggered using Ag(I) ions; subsequently, Au(III) ions were employed to convert the variable-composition Au_18−xAg_x(GSH)₁₄ NCs into fixed-composition alloy Au₂₆Ag(GSH)₁₇Cl₂ NCs. Monitoring of the alloying process showed that the formation of Au_18−xAg_x(GSH)₁₄ NCs proceeds through the two electron-hopping events (2e⁻ Au₁₅ → 2e⁻ (AuAg)_15–17 → 4e⁻ (AuAg)_18–19 → 4e⁻ (AuAg)₁₈), whereas the transformation of (AuAg)₁₈ into Au₂₆Ag mainly involved the formation of intermediate species Au₂₆(GSH)₁₇Cl_n (n = 0–2). Moreover, we determined that the single Ag atom in Au₂₆Ag NCs resides on the NC surface. This study not only provides a novel strategy for the synthesis of water-soluble alloy NCs but also contributes to the fundamental understanding of the alloying mechanism of metal NCs.