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.