A Critical Size for Emergence of Nonbulk Electronic and Geometric Structures in Dodecanethiolate-Protected Au Clusters

We report on how the transition from the bulk structure to the cluster-specific structure occurs in n-dodecanethiolate-protected gold clusters, Aun(SC12)(m). To elucidate this transition, we isolated a series of Aun(SC12)(m) in the n range from 38 to similar to 520, containing five newly identified or newly isolated clusters, Au-104(SC12)(45), Au-similar to 226(SC12)(similar to 76), Au-similar to 253(SC12)(similar to 90), Au-similar to 356(SC12()similar to 112), and Au-similar to 520(SC12)(similar to 130), using reverse-phase high-performance liquid chromatography. Low-temperature optical absorption spectroscopy, powder X-ray diffractometry, and density functional theory (DFT) calculations revealed that the Au cores of Au-144(SC12)(60) and smaller clusters have molecular-like electronic structures and non-fcc geometric structures, whereas the structures of the Au cores of larger clusters resemble those of the bulk gold. A new structure model is proposed for Au-104(SC12)(45) based on combined approach between experiments and DFT calculations.