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 <i>n</i>-dodecanethiolate-protected gold clusters, Au_<i>n</i>(SC12)_<i>m</i>. To elucidate this transition, we isolated a series of Au_<i>n</i>(SC12)_<i>m</i> in the <i>n</i> range from 38 to ∼520, containing five newly identified or newly isolated clusters, Au₁₀₄(SC12)₄₅, Au_∼226(SC12)_∼76, Au_∼253(SC12)_∼90, Au_∼356(SC12)_∼112, and Au_∼520(SC12)_∼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 Au₁₄₄(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 Au₁₀₄(SC12)₄₅ based on combined approach between experiments and DFT calculations