Planar pentacoordinate silicon and germanium atoms

Abstract

The global minimum of XMg₄Y⁻ (X = Si, Ge; Y = In, Tl) and SiMg₃In₂ contains a planar pentacoordinate atom of group 14 other than carbon. Its design is based on the “localization” approach, replacing one or two peripheral atoms in XMg₅²⁻ by more electronegative ones. This change diminishes the repulsion and leads to stronger covalent X–Y bonds, stabilizing the planar pentacoordinate atom species.