Formation Mechanism of Au₂₀(SR)₁₆

Understanding the formation mechanism is crucial for the synthesis and regulation of thiolate-protected gold nanoclusters at the atomic level. In this study, we elucidate the formation mechanism of a specially structured Au₂₀(SR)₁₆ cluster with a Au₈(SR)₈ ring. Utilizing density functional theory calculations, we propose an intermolecular coupling and hydrolysis reaction mechanism to elucidate the formation of Au₂₀(SR)₁₆ within the NaBH₄ system. Additionally, we formulate a molecular-like reaction equation to elucidate the size evolution of thiolate-protected gold nanoclusters, ranging from 0e ^- Au₁₂(SR)₁₂ to 4e ^- Au₂₀(SR)₁₆ clusters during the initial nucleation stage of growth. Notably, 0e ^- Au₁₂(SR)₁₂ exhibits a ring-in-ring structure, deviating from the conventional interlocked catenane ring. Furthermore, we delineate the formation pathway of 4e ^- Au₂₀(SR)₁₆, leveraging 0e ^- Au₁₂(SR)₁₂ as a seed based on the bottom-up reaction equation. These systematic investigations into the formation mechanism of 4e ^- Au₂₀(SR)₁₆ are pivotal for comprehending the NaBH₄ reduction and hydrolysis process and elucidating the structure-property relationship of Au₂₀(SR)₁₆. To the best of our knowledge, this represents the great theoretical exploration of the growth pathway from ring-in-ring structures to small gold clusters, offering valuable insights into the precise synthesis of gold clusters.