Mixed Si/Ge Nine-Atom Zintl Clusters: ESI Mass Spectrometric Investigations and Single-Crystal Structure Determination of Paramagnetic [Si9–xGex]3–

Mixed Si/Ge compounds are of special interest as potential materials for photovoltaic applications. In order to evaluate the usage of soluble precursor compounds, we investigated the synthesis of heteroatomic nine-atom clusters that consist of Si and Ge atoms through dissolution of the ternary Zintl phases K12Si17–xGex (x = 9, 12) and Rb12Si17–xGex (x = 9). Electrospray ionization (ESI) mass spectrometry demonstrates the presence of mixed Si9–xGex clusters in acetonitrile solution. From ammonia solutions of the ternary phases, four compounds that contain 3-fold negatively charged [Si9–xGex]3– clusters are obtained. The paramagnetic behavior is confirmed by EPR spectroscopy. [E9]3– Zintl clusters are considered as intermediate structures in the stepwise oxidation of [E9]4– clusters to novel element allotropes (E = Si–Pb). The structure of Rb­[Rb-crypt]2[Si2.3(1)Ge6.7(1)]­(NH3)7 and the isostructural structures of [Rb-crypt]3[Si2.2(1)Ge6.8(1)]­(NH3)8, [K-crypt]3[Si2.4(1)Ge6.6(1)]­(NH3)8.5, and [K-crypt]3[Si4.6(1)Ge4.4(1)]­(NH3)8.5 are investigated by single-crystal X-ray diffraction (crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane). The Si/Ge ratio of the products correlates with the composition of the ternary precursor phases.