A homoleptic alkynyl-protected [Ag9Cu6(tBuCC)12]+ superatom with free electrons: synthesis, structure analysis, and different properties compared with the Au7Ag8 cluster in the M15+ series

We report the first homoleptic alkynyl-protected AgCu superatomic nanocluster [Ag9Cu6((BuC)-Bu-t C)(12)](+) (NC 1, also Ag9Cu6 in short), which has a body-centered-cubic structure with a Ag-1@Ag-8@Cu-6 metal core. Such a configuration is reminiscent of the reported AuAg bimetallic nanocluster [Au-1@Ag-8@Au-6((BuC)-Bu-t C)(12)](+) (NC 2, also Au7Ag8 in short), which is also synthesized by an anti-galvanic reaction (AGR) approach with a very high yield for the first time in this study. Despite a similar Ag-8 cube for both NCs, structural anatomy reveals that there are some subtle differences between NCs 1 and 2. Such differences, plus the different M-1 kernel and M-6 octahedron, lead to significantly different optical absorbance features for NCs 1 and 2. Density functional theory calculations revealed the LUMO and HOMO energy levels of NCs 1 and 2, where the characteristic absorbance peaks can be correlated with the discrete molecular orbital transitions. Finally, the stability of NCs 1 and 2 at different temperatures, in the presence of an oxidant or Lewis base, was investigated. This study not only enriches the M-15(+) series, but also sets an example for correlating the structure-property relationship in alkynyl-protected bimetallic superatomic clusters.

Automated summary

In this study, the first homoleptic alkynyl-protected AgCu superatomic nanocluster was reported, along with a similar structure bimetallic nanocluster. Despite the similar Ag-8 cube structure, subtle differences exist between the two clusters, resulting in significantly different optical absorbance features.