Sub-stoichiometric reactions are powerful tools for mechanistic analyses because they can stabilize key intermediates in chemical reactions. Here, we develop a multiple-step, sub-stoichiometric reduction platform that can precisely dope required electrons to synthesize atomically precise gold nanoclusters (Au NCs). Only a sub-stoichiometric amount of NaBH₄ (equivalent to doping one valence electron into Au NCs) is introduced in each step. In 8 successive steps, we identify a series of stable intermediates whose relative abundance suggests a different growth pathway from previous reports. In addition, detailed analysis of 120 real-time mass spectra during the formation process reveals three meta-stable species. Moreover, the platform also sheds light on the structural evolution of Au NCs during the growth process. This method provides a platform for studying the molecular- and atomic-level evolution of metal NCs (in both size and structure), revealing the reaction dynamics of NC intermediates toward the formation of atomically precise metal NCs.

亚化学计量反应是机械分析的强大工具，因为它们可以稳定化学反应中的关键中间体。在这里，我们开发了一个多步，亚化学计量的还原平台，该平台可以精确地掺杂所需的电子以合成原子精确的金纳米团簇（Au NCs）。仅亚化学计量的NaBH ₄在每个步骤中引入（相当于将一个价电子掺杂到Au NCs中）。在8个连续的步骤中，我们确定了一系列稳定的中间体，其相对丰度表明与先前报道不同的生长途径。此外，在形成过程中对120个实时质谱的详细分析揭示了三个亚稳态物种。此外，该平台还阐明了金纳米碳管在生长过程中的结构演变。该方法为研究金属NC的分子和原子级演化（在尺寸和结构上）提供了一个平台，揭示了NC中间体对形成原子精确的金属NC的反应动力学。