Self-organization of nanosized gold particles

Naked colloidal gold solutions have been prepared in toluene using a two-phase system. The phase-transfer reagent used, a quaternary ammonium bromide salt (R4N+Br-), is specifically adsorbed on the clusters through the formation of surface ion pairs, probably with the Br- ion attached to the Au surface. The separation between clusters for two-dimensional structures is dependent on the chain length in R4N+. When more than one layer is present, the nanosized particles show unusual self-organization properties: the occupancy of 2-fold saddle sites is preferred to that of 3-fold hollow sites, leading to linear and circular arrangements. It is proposed that this is due to the balance between local electrostatic repulsion and dispersion forces between the particles.