A homoleptic alkynyl-protected [AgCu( BuC[triple bond, length as m-dash]C)] superatom with free electrons: synthesis, structure analysis, and different properties compared with the AuAg cluster in the M series.

We report the first homoleptic alkynyl-protected AgCu superatomic nanocluster [AgCu( BuC[triple bond, length as m-dash]C)] (NC , also AgCu in short), which has a body-centered-cubic structure with a Ag@Ag@Cu metal core. Such a configuration is reminiscent of the reported AuAg bimetallic nanocluster [Au@Ag@Au( BuC[triple bond, length as m-dash]C)] (NC , also AuAg 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 cube for both NCs, structural anatomy reveals that there are some subtle differences between NCs and . Such differences, plus the different M kernel and M octahedron, lead to significantly different optical absorbance features for NCs and . Density functional theory calculations revealed the LUMO and HOMO energy levels of NCs and , where the characteristic absorbance peaks can be correlated with the discrete molecular orbital transitions. Finally, the stability of NCs and at different temperatures, in the presence of an oxidant or Lewis base, was investigated. This study not only enriches the M series, but also sets an example for correlating the structure-property relationship in alkynyl-protected bimetallic superatomic clusters.