Electronic Stability of Bimetallic Au$ _{\textbf{2}} $@Cu$ _{\textbf{6}} $ Nanocluster: Closed-Shell Interaction and Multicenter Bonding

Metallophilic interaction is a unique type of weak intermolecular interaction, where the electronic configuration of two metal atoms is closed shell. Despite its significance in multidisciplinary fields, the nature of metallophilic interaction is still not well understood. In this work, we investigated the electronic structures and bonding characteristic of bimetallic Au$ _{2} $@Cu$ _{6} $ nanocluster through density functional theory method, which was reported in experiments recently [Angew. Chem. Int. Ed. 55 , 3611 (2016)]. In general thinking, interaction between two moieties of (CuSH)$ _{6} $ ring and (Au$ _{2} $PH$ _{3} $)$ _{2} $ in the Au$ _{2} $@Cu$ _{6} $ nanocluster can be viewed as a d$ ^{10} $-$ \sigma $ closed-shell interaction. However, chemical bonding analysis shows that there is a ten center-two electron (10c-2e) multicenter bonding between two moieties. Further comparative studies on other bimetallic nanocluster M$ _{2} $@Cu$ _{6} $ (M = Ag, Cu, Zn, Cd, Hg) also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d$ ^{10} $-$ \sigma $ closed-shell interaction. This will provide valuable insights into the understanding of closed-shell interactions.