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

A facile preparative route to alkanethiolate (Cn) Au-38 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 Au-38 nanoparticles are prepared in similar to 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 Au-38 nanoparticles. Voltammetry of these Au-38 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 Au-38 nanoparticles can thus be described as a sum of electron addition energies and the discrete electronic energy levels of the Au-38 core.