Carbon Monoxide: A Mild and Efficient Reducing Agent towards Atomically Precise Gold Nanoclusters

In recent years, thiolate-protected gold nanoclusters (or thiolated Au NCs) with a core size below 2 nm have emerged as a new class of multifunctional nanoparticles because of their unique molecular-like properties and the potential to use these properties in many practical applications. A general synthesis of Au NCs may involve the use of a strong reducing agent (e.g., sodium borohydride (NaBH4)), which often leads to the formation of mix-sized Au NCs if no delicate control is applied. To obtain atomically precise Au NCs, additional physical or chemical selection processes (e.g., high-resolution separation or size-focusing) are required, which are difficult to be scaled up or are limited to only thermodynamically stable products. By introducing a milder reducing agent - carbon monoxide (CO) - both stable and metastable thiolated Au NCs, including Au10-12, Au-15, Au-18, Au-25, and Au-29, can be synthesized in a one-pot manner. In addition, CO reduction also enables the synthesis of a highly luminescent Au-22(SG)(18) NC. Furthermore, the intermediates of Au NC growth can be tracked in the CO-reduction system due to the mild and readily stoppable nature of CO reduction. Therefore, the use of CO reduction may bring new flexibilities in designing synthetic strategies and understanding the growth mechanism of atomically precise Au NCs, which could contribute to a better design of functional Au NCs, further paving their way towards practical applications in various fields.