Gold and sulfur assemble into small, stable anionic clusters that are either hollow or contain a single atom in the center, according to theoretical work published in ACS Nano that describes the structures and electronic properties of this class of clusters for the first time (DOI: 10.1021/nn103217z). The study, which focused on gold sulfide clusters containing up to 15 gold atoms, deepens understanding of the composition, stability, and other properties of metal-based clusters. The investigation also aids interpretation of recent results of ion-mobility mass spectrometry experiments indicating that some of the clusters are particularly stable. Yong Pei and Xiao Cheng Zeng of the University of Nebraska, Lincoln, and coworkers found that the high stability of the S–Au–S structural unit supports formation of various hollow clusters, including Au6S4 –, Au9S6 –, and Au12S8 –, which exhibit tetrahedron, triangular prism, and cuboctahedron structures, respectively. The stability of the S–Au–S building motif also leads to clusters with a gold atom encapsulated in a polyhedron such as Au11S6 –, which has triangular prism geometry, as well as clusters such as Au9S5 –, which adopts a unique pyramidal structure.