Facile preparative route to alkanethiolate-coated Au₃₈ nanoparticles: Postsynthesis core size evolution

A facile preparative route to alkanethiolate (Cn) Au₃₈ nanoparticles, where n = 4, 6, 8, 10, and 12, is described. Subnanometer-sized nanoparticles are initially produced by a modified Brust synthesis, which undergo core-size evolution upon removal of reaction impurities that have served as additional protecting layers. C4-C12 Au₃₈ nanoparticles are prepared in ∼300 mg quantities by the selective removal of reaction impurities with dimethyl sulfoxide. The prepared nanoparticles are 1.1 -1.2 nm in core size, and all exhibit optical and electrochemical characteristics of Au₃₈ nanoparticles. Voltammetry of these Au₃₈ nanoparticles reveals that the energy gap between the first one-electron oxidation and the first reduction is rather insensitive to the ligand employed. By contrast, the energy gaps between the first and second oxidations and between the second and third oxidations are ligand-dependent; both substantially increase with ligand thickness. The charging energetics of alkanethiolate-coated Au₃₈ nanoparticles can thus be described as a sum of electron addition energies and the discrete electronic energy levels of the Au ₃₈ core.