[Sn-8](6-)-Bridged Mixed-Valence Zn-I/Zn-II in {[K2ZnSn8(ZnMes)](2)}(4-) Inverse Sandwich-Type Cluster Supported by a Zn-I-Zn-I Bond

摘要

Since [Sn-8](6-) was discovered from the solid-state phase in 2000, its solution chemistry has been elusive due to the high charges and chemical activity. Herein, we report the synthesis and characterization of an inverse sandwich-type cluster dimer {[K2ZnSn8(ZnMes)](2)}(4-) (1 a), in which the highly charged [Sn-8](6-) is captured by mixed-valence Zn-I/Zn-II to form the dimer {closo-[Zn2Sn8]}(2) moieties bridged by a Zn-Zn bond. Such Zn-Sn cluster not only exhibits a novel example of mixed-valence Zn-I/Zn-II for stabilizing highly active anion species, but also indicates the [Sn-8](6-) cluster can act as a novel bridging ligand, like arene, with a eta(4):eta(4)-fashion. Theoretical calculations indicate that a significant delocalization of electrons over Zn atoms plays a vital role in the stabilization of the [Sn-8](6-) species. The AdNDP and magnetic response analyses clearly showed the presence of local sigma-aromaticity in three cluster fragments: two ZnSn4 caps and Sn-8 square antiprism.