Structures Of Neutral Gold Clusters Revealed

Gold nanoparticles are touted for their ability to oxidize carbon monoxide in applications such as cleaning up automobile exhaust. In particular, atoms at the edges of gold clusters are thought to be catalytically reactive due to their low coordination to other atoms. Spectroscopic techniques used to study the electronic and geometric structures of these nanoparticles have been limited to charged clusters, however. A team led by André Fielicke of the Fritz Haber Institute of the Max Planck Society, in Berlin, has now used a far-infrared vibrational spectroscopy technique to determine the gas-phase structures of three neutral gold clusters: Au₂₀, Au₁₉, and Au₇ (Science 2008, 321, 674). Neutral Au₂₀ has the same symmetrical pyramid structure as its analogous anion, Au₂₀^-, the researchers observed. But neutral Au₇ has a structure distinct from either its cationic or anionic forms. The change in Au₇'s structure as its electron density increases from the cationic, to neutral, to anionic forms corresponds to a decrease in average atom coordination, the researchers found. This shift facilitates binding of molecules such as CO that would not ordinarily bind to gold atoms with higher coordination numbers, Fielicke says.