Cluster of clusters: A new series of high nuclearity Au-Ag clusters

The structure of a novel series of bimetallic Au-Ag clusters containing 25 (Au13Ag12), 37 (Au18Ag19), and 38 (Au18Ag20) metal atoms is discussed. The most interesting structural characteristic of these clusters is that they can be considered as being built from 13-atom centred icosahedral cluster units. Thus, the 25-atom cluster can be considered as two icosahedra sharing a vertex; the 37− and 38-atom clusters as three icosahedra sharing three vertices in a cyclic manner plus one and two capping atoms, respectively. These observations led to the concept of "cluster of clusters". It is predicted that tetrahedral, trigonal-bipyramidal, and pentagonal-bipyramidal arrays of vertex-sharing icosahedra will give rise to nuclearities (10n + 6) of 46−, 56− and 76-atom clusters, respectively. One exception to the rule is the 127-atom icosahedral cluster which is formed by 12 centred icosahedra sharing 30 corners. Here the icosahedral hole created by the 12 icosahedra is filled with one additional atom. It is suggested that the idea of "cluster of clusters" may provide new pathways to novel high nuclearity supraclusters via vertex-, edge-, and face-sharing and/or close-packing of smaller cluster units as building blocks.