New Insight into Intermediate Precursors of Brust–Schiffrin Gold Nanoparticles Synthesis

There is an ongoing intensive debate on the mechanism of gold nanoparticles formation regarding the intermediate precursors prior to the addition of reducing agent. A new detailed view of the widely used Brust–Schiffrin two-phase method to prepare gold nanoparticles is presented here. Precursor species of these reactions have been identified and quantified by NMR, UV–visible, Fourier-transform Raman spectroscopy, etc. We demonstrate that tetraalkylammonium gold complexes ([TOA]­[AuX₂]) and soluble gold thiolate ([TOA]­[AuSRX] and [TOA]­[Au­(SR)₂]) were detectable as the precursors by NMR spectroscopy. Their relative contents depend on the concentration of reactants. Higher concentration of the reactants is favorable for the formation of soluble thiolate. Polymeric gold thiolate [Au­(I)­SR]_n could eventually precipitate from the solution under specific conditions. The clear mechanism presented here is of great significance to tailor the size and properties of the final products.