Deciphering chemical bonding in golden cages.

The recently developed adaptive natural density partitioning (AdNDP) method has been applied to a series of golden clusters. The pattern of chemical bonding in Au(20) revealed by AdNDP shows that 20 electrons form a four-center-two-electron (4c-2e) bond in each of 10 tetrahedral cavities of the Au(20) cluster. This chemical bonding picture can readily explain the tetrahedral structure of the Au(20) cluster. Furthermore, we demonstrate that the recovered 4c-2e bonds corresponding to independent structural fragments of the cluster provide important information about chemically relevant fragmentation of Au(20). In fact, some of these bonds can be removed from the initial tetrahedral structure together with the associated atomic fragments, leading to the family of smaller gold clusters. Chemical bonding in the systems formed in such a manner is yet closely related to the bonding in the parental systems showing persistence of the 4c-2e bonding motif. Thus, the multicenter bonds in golden cages recovered by the AdNDP analysis correspond to the fragments that should be seen as building blocks of these chemical systems.