Bonding Interaction Within Concentric Structural Layers in Gold Superatoms. The Concentric Bond.

Ligand-protected gold clusters display a rich structural diversity, featuring remarkable structures such as Au(SR), Au(PPh)Cl, and CuAu(SR) , involving a central core composed of consecutive layers. The respective Au@Au, Au@Au@Au and Cu@Au@Au@Au cores with concentric structural layers enable a variable bonding/antibonding character between the electronic shells ascribed to each layer. Here, we rationalize the bonding within concentric structural layers in order to gain a further understanding of the related bonding patterns in such species. The proposed bonding concept differs from the classical situation in adjacent atoms, now being considered between concentric shells and, thus, coined as the concentric bond. From this approach, the bonding/antibonding character of each concentric shell is evaluated, and its contribution to the overall bonding is discussed. The concentric bond enables building a clear picture of the bonding acting in the overall cluster under the superatom concept. Such an approach expands the understanding of multi-layered cluster cores and is useful to further rationalize the bonding situation in metallic nanostructures.