Structural characteristics of mixed nido‐[Si_9−xGe_x]⁴⁻ (x=1, 2) Zintl clusters in solution and within solvent crystals

Abstract

Dedicated to Professor Wolfgang Schnick on the Occasion of his 65 th BirthdayMixed Zintl-type anionic clusters of silicon and germanium comprise an important class of potential materials in electronic applications. Herein, we present quantum chemical investigations to describe the mixing behavior of Si and Ge within [Si 9À x Ge x ] 4À (x = 0, 1, 2) Zintl anions that can be considered as precursors for novel SiÀ Ge materials. To understand the mixing behavior of such clusters in solution, we analyze the molecular clusters at using Density Functional Theory (DFT) and Coupled Cluster methods. Systematic assessment of relative energies of various structural isomers indicates that there is a preference to substitute Si with Ge in the open square of the monocapped square antiprismatic [Si 8 Ge] 4À and [Si 7 Ge 2 ] 4À clusters. Population analysis reveals that the highest negative partial charge is also located at these positions. Investigation of Rb 4 Si 9À x Ge x (NH 3 ) 5 solvent crystals using DFT methods and periodic boundary conditions further elucidates the behavior during crystallization. It is shown that in addition to the favored [Si 8 Ge] 4À open-square isomers arising in solution, the weak intermolecular interactions in the crystalline environment affect which structural isomers are observed in the crystal structure. The experimentally observed Ge site occupations could be explained by analysis of their energetics. This analysis contributes to the understanding of the mixing behavior of these important building blocks for material design.