Most nanoparticle syntheses, including those based on the Brust-Schiffrin method, produce a mixture of different metal core sizes. This report presents a new strategy for controlling the size and dispersity of ultra-small nanoclusters through selection of the metal complex distribution during syntheses. These one-pot syntheses manipulate complex distributions from the gold precursor, AuClPPh3 (PPh3 = triphenylphosphine), and L6 (L6 = 1,6-bis(diphenylphosphino)hexane) ligand prior to reduction with NaBH4 prepared in 1:1 methanol:chloroform solutions. Monodisperse nanoclusters of distinct nuclearity are obtained for specific ligand ratios: [L6]/[PPh3] = 4, yields [Au8L64]2+, [L6]/[PPh3] = 0.4 yields [Au9L64Cl]2+, and [L6]/[PPh3] > 8 yields ligated Au10 cores in the form of [Au10L64]2+ and [Au10L65]2+. Polyhedral skeletal electron pair theory can account for the stability of [Au9L64Cl]2+, which is the smallest closed-shell chlorinated cluster reported, thus far. Temporally measured electrospray mass spectrometry (ESI-MS) and UV-Vis spectra indicate that [Au9L64Cl]2+ and Au10 species result from reactions involving [Au8L64]2+. The synthesis of small gold clusters containing chloride ligands opens up the possibility of using them as building blocks for larger clusters protected by diphosphine ligands and for other novel thiol and phosphine protected compounds via ligand exchange.
Citation: Journal of Physical Chemistry Letters
Pub Type: Journals
diphosphine ligand, gold nanoparticle, ligand exchange, mass spectrum, nanocluster, nanoparticle synthesis, nanoparticle, optical spectrum, phosphine ligand, synthesis