Direct self-focusing synthesis of monodisperse [Au(PPh)] nanoclusters.

Direct and scalable synthesis of monodisperse gold nanoclusters is highly desired but remains a great challenge due to the complexity of chemical reactions. In this regard, a suitable precursor is important as it can simplify the synthesis processes and offer controllability in tuning the product. In this study, we found that Au(PPh)Cl could be used as an effective precursor for the direct synthesis of atomically monodisperse [Au(PPh)] nanoclusters without the need of tedious post-synthetic purification steps. The Au(PPh)Cl precursor could be directly reduced by NaBH (0.25 molar equivalent) in a dichloromethane solution; this produced Au clusters with a 35% reaction yield. Time-dependent mass spectrometry and in situ UV-vis absorption spectroscopy reveal that the synthesis process is initiated by the rapid formation of the Au-Au mixture, followed by a slow spontaneous self-focusing process that converges the mixture into atomically monodisperse Au. The success of this direct synthesis has been hypothesized to arise from the relatively stronger Au(i)Au(i) aurophilic attraction between Au(i)-PPh complexes that facilitates the aggregation of Au(i)-PPh on Au(0) cores.