Multicenter Bonds Define Golden Cages

A theoretical method devised by Dmitry Yu. Zubarev and Alexander I. Boldyrev of Utah State University has permitted the scientists to decipher the chemical bonding pattern in small hollow gold clusters (J. Phys. Chem. A, DOI: 10.1021/jp808103t). Gold clusters have stimulated a boom in the design of molecular electronics and nanocatalysts. Unraveling how the clusters are built is expected to provide information on structure-activity relationships to help advance those applications. Earlier this year, Zubarev and Boldyrev reported a new algorithm, named adaptive natural density partitioning (AdNDP), which partitions the electron density of a molecule into electron pairs per the smallest possible molecular fragment (Phys. Chem. Chem. Phys. 2008, 10, 5207). The researchers applied AdNDP to the pyramid-shaped Au₂₀ cluster and found that 20 valence electrons form 10 four-center, two-electron bonds—where four gold atoms share an electron pair. The pattern represents one bond for each four-atom tetrahedral unit that exists in the cluster. This bonding picture explains the overall tetrahedral shape of Au₂₀, the researchers say, and establishes the four-atom unit as the likely building block of other gold clusters.