Zwitterionic Thiolate-Protected Ag22(0/I) and Ag20(I) Clusters: Assembly, Structural Characterization, and Antibacterial Activity.

ABSTRACT

Zwitterionic thiolate ligands have the potential to introduce novel assembly modes and functions for noble metal clusters. However, their utilization in the synthesis of silver clusters remains understudied, particularly for the clusters containing reductive Ag(0) species. In this article, we report the first synthesis of a mixed-valence silver(0/I) cluster protected by zwitterionic Tab as thiolate ligands (Tab = 4-(trimethylammonio)benzenethiolate), denoted as [Ag22(Tab)24](PF6)20·16CH3OH·6Et2O (Ag22·16CH3OH·6Et2O), alongside an Ag(I) cluster [Ag20(Tab)12(PhCOO)10(MeCN)2(H2O)](PF6)10·11MeCN (Ag20·11MeCN). Ag22 has a distinct hierarchical supratetrahedral structure with a central {Ag6} kernel surrounded by four [Ag4(Tab)6]4+ units. High-resolution electrospray ionization mass spectra demonstrate that Ag22 has two free electrons, indicating a superatomic core. Ag20 has a drum-like [Ag12(Tab)6(PhCOO)6(H2O)]6+ inner core capped by two tetrahedral-like [Ag4(Tab)3(PhCOO)2(MeCN)]2+ units. Ag20 can be transformed into Ag22 after its reaction with NaBH4 in solution. Antibacterial measurements reveal that Ag22 has a significantly lower minimum inhibitory concentration than that of the Ag20 cluster. This work not only extends the stabilization of silver(0/I) clusters to neutral thiol ligands but also offers new materials for the development of novel antibacterial materials.