Endohedral group-14 clusters Au@X12 (X = Ge, Sn, Pb) and their anions: A first-principles study

Abstract

Group-14 (Ge, Sn, Pb) clusters have attracted a lot of attention not only because of their unique structural models but also the outstanding building blocks as cluster-assembled materials. In this paper, we have systematically investigated the structure, chemical stability, electronic property, spherical aromaticity, and bonding of neutral Au@X12 (X = Ge, Sn, Pb) clusters and their anions using density-functional theory (DFT) calculations. It is found that the Au@Ge12 cluster displays bicapped pentagonal prism geometry, whereas Au@X12 (X = Sn, Pb) possess the perfect icosahedral geometry. Analysis of binding energy reveals that the species exhibit high chemical stabilities, especially for closed-shell anionic clusters, which contain 60 valence electrons. The hybridization between cage and Au enhances the chemical stability of clusters, while the enhanced stability can be explained by spherical aromaticity, confirmed by largely negative NICS values, of which eight π electrons satisfy 2(N + 1)2 counting rule, forming 2S22P6 set. The AdNDP analysis reveals that the delocalized chemical bonding is responsible for structural stabilization of clusters, e.g., eight delocalized 4c-2e σ-bonds on inner shell and five delocalized 4c-2e σ-bonds on outer shell. To summarize, the calculated results will provide further understanding for the design of novel building blocks as cluster-assembled nanomaterials.