The formation of ligand-protected transition metal nanoclusters in size-selective syntheses is driven by the inherent properties of the protecting ligands. We have previously reported the selective, monodisperse product formation of phosphine protected Au8, chlorinated Au9 and Au10 clusters, but a general description of how the ligands produce size-selective products is necessary to develop a predictive model for cluster formation. The current study used phosphine-protected Au clusters as a model system to examine i) the metal ligand complex distributions in methanol:chloroform solutions as a function of Au:ligand ratio, ii) the role of oxidation on the complex distribution and iii) nanocluster formation after reduction with NaBH4 as a function of complex distribution. The initial complexes formed in solution are shown to not only control ligand formation, but also have strong correlation to specific synthetic pathways for product formation. Specifically, 1,n-bis(diphenylphosphino)alkane ligands, where n = 1-6 representing methane through hexane carbon backbones, are examined and split into two distinct classes based on Au:Ln complex formation. The classes form predominately either [AuLn2]+ (Class I, n = 1-3) or [Au2Ln2]2+ (Class II, n = 4-6) and the subsequent nanocluster formations after reduction are directly related to the initial complex distributions. Classification of the phosphine ligand:Au complexes allows for the first predictable syntheses of ligated Au clusters by simply monitoring the initial complex distribution.
Pub Type: Journals
ESI-MS, nanoparticle, monodisperse, monolayer-protected cluster, nucleation, reduction