Predictive Gold Nanocluster Formation Controlled by Metal-Ligand Complexes

The formation of ligand‐protected gold nanoclusters during size‐selective syntheses is seemingly driven by the inherent properties of the protecting ligands, but a general description of the product formation has not been presented. This study uses diphosphine‐protected Au clusters as a model system to examine i) control of metal‐ligand complex distributions in methanol–chloroform solutions, ii) role of solution perturbations, e.g., oxidation, and iii) nanocluster formation through reduction of characterized complex distributions. By selectively reducing complexes and monitoring cluster formation with electrospray ionization mass spectrometry and UV–vis, data show the distribution of complexes can be controlled through ligand exchange, and the reduction of specific complexes produce characteristic ligated gold clusters based on ligand class. Specifically, 1,n‐bis(diphenylphosphino)n‐alkane ligands, Ln, where n = 1 through 6, are classified into two distinct sets. The classes represent ligands that either form mainly [AuLn2]+ (Class I, n = 1–3) or bridged [Au2Ln2]2+ (Class II, n = 4–6) complexes after complete ligand exchange with AuClPPh3. Selectively reducing gold‐phosphine ligand complexes allows mapping of product formation, resulting collectively in a predictive tool for ligated gold cluster production by simply monitoring the initial complex distribution prior to reduction. Selective reduction of gold‐diphosphine complexes produces predictable nascent gold nanoclusters that can be separated into two classes. Class I complexes produce nascent neutral clusters and Class II produce cationic, ligated Au8 and Au10 nanoclusters. Predictable nascent products allow further tunable control of metal nuclearity through postreduction, size‐selective processing, when desired.