Controlled Etching of Au:SR Cluster Compounds

When Au:SR cluster compounds (R = (CH₂)₅CH₃) with an Au metallic cluster core mass of ∼14 kDa (∼75 atoms, 1.1 nm equivalent diameter), are heated in neat dodecane-thiol solution under inert atmosphere, species with smaller Au core masses are formed, presumably by the removal of Au atoms from the outermost surface layer of the cluster's Au core. This process was monitored through laser desorption mass spectrometry, optical absorption spectroscopy, and X-ray diffraction, where all three methods indicate a substantial decrease (>50%, by mass or number of Au atoms) in the size of the cluster compound's inorganic core. The optical absorption spectra and laser desorption mass spectra of the compounds generated by etching are strikingly similar to compounds previously separated without an etching step. The dual function of the thiol as both stabilizing adsorbate and efficient etchant sets this cluster (or nanocrystal) system apart from other metallic and semiconductor systems.