Synthetic Approach for Tunable, Size-Selective Formation of Monodisperse, Diphosphine-Protected Gold Nanoclusters

We report a new strategy that provides stringent control for the size and dispersity of ultrasmall nanoclusters through preparation of gold complex distributions formed from the precursor, AuClPPh3 (PPh3 = triphenylphosphine), and the L-6 (L-6 = 1,6-bis(diphenylphosphino) hexane) ligand prior to reduction with NaBH4 in 1:1 methanol/chloroform solutions. Monodisperse nanoclusters of distinct nuclearity are obtained for specific ligand ratios; [L-6]/[PPh3] = 4 yields [Au8L46](2+), [L-6]/[PPh3] = 0.4 yields [(Au9L4Cl)-Cl-6](2+), and [L-6]/[PPh3] = 8 yields ligated Au-10 cores in the form of [Au10L46](2+) and [Au10L56](2+). Polyhedral skeletal electron pair theory accounts for the stability of [(Au9L4Cl)-Cl-6](2+), which is the smallest closed-shell chlorinated cluster reported. Electrospray mass spectrometry and UV-vis spectra indicate that [(Au9L4Cl)-Cl-6](2+) and [Au10Lx6](2+) (x = 4, 5) result from reactions involving [Au8L46](2+). Syntheses of small gold clusters containing chloride ligands open the possibility of constructing larger clusters via ligand exchange.