Crystal Structure of the Protonated Germanide Cluster [HGe9]3−

Abstract

A single crystal X-ray diffraction study of the new compound [Rb([2.2.2]crypt)]2[Rb([18]crown−6)][HGe9]·4NH3 revealed the presence of the first protonated nine-atom germanide cluster [HGe9]3−. It forms from Rb4Ge9 in liquid ammonia, so that [Ge9]4− can be considered as the base and [HGe9]3− its formally conjugated acid. The H atom is attached to a germanium vertex atom of the basal square plane, as it is known for [RGe9]3− (R = C5H9, Mes, etc.) or [HE9]3− (E = Si, Sn). In addition, the proton could be located unambiguously in the Fourier difference map. [HGe9]3− also represents a nido cluster species with 22 cluster-bonding electrons, which can be considered the most stable structure for nine-atom cluster species for all group 14 elements.