A Ring Model for Understanding How Interfacial Interaction Dictates the Structures of Protection Motifs and Gold Cores in Thiolate-Protected Gold Nanoclusters

Abstract Understanding the role of interfacial interactions between the protection motifs SR[Au(SR)]x (x = 0, 1, 2, 3, ...) and gold cores on the stabilities of the thiolate-protected gold nanoclusters is still a challenging task. Although several theoretical models, including the superatom complex, super valence bond, and superatom network, have provided insights into the stabilities of either the overall structures or the gold cores, a model that can illuminate how the interfacial interaction dictates the unique structures of the protection motifs and gold cores is still lacking. Herein, we present a ring model, on the basis of comprehensive analyses of all 95 previous experimentally crystallized and theoretically predicted thiolate-protected gold nanoclusters, to offer a deeper insight into the structure-interaction relationship for this class of clusters. In the ring model, all the thiolate-protected gold nanoclusters can be generically viewed as fusion or interlocking of several [Aum(SR)n] (m = 4 - 8, 10, 12, and 0 ≤ n ≤ m) rings. The aurophilic interactions among these rings are expected to play a key role in the stabilization of the thiolate-protected gold nanoclusters. Guided by the ring model and the grand unified model (for understanding the structures of gold cores), a new Au42(SR)26 isomer is predicted, whose total energy is even lower than those of two previously crystallized isomers, thereby giving credence to the predictability of the ring model. The ring model provides not only a mechanistic understanding of the interactions between the protection ligands and gold cores in the thiolate-protected gold nanoclusters, but also a practical guidance on predicting new thiolate-protected gold nanoclusters for experimental synthesis and confirmation.