Syntheses and Structures of the Germanides CaNiGe and MgCoGe as well as Chemical Bonding in CaNiGe and CaNi 2 Ge 2

The intermetallic germanides CaNiGe and MgCoGe have been synthesized from the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffractions both on powders and single crystals: CeFeSi structure type, P 4/ nmm , a = 4.19341(3), c = 6.6264(1) Å, w R2 = 0.030, 124 F 2 values, 10 variable parameters for CaNiGe and a = 3.8960(4), b = 6.1929(11) Å, w R2 = 0.048, 104 F 2 values, 10 variable parameters for MgCoGe. In CaNiGe and MgCoGe the transition metal and germanium atoms build [ T Ge] layers ( T = Ni, Co), which are separated by the calcium and magnesium atoms, respectively. The crystal structures of CaNiGe and MgCoGe as well as chemical bonding in CaNiGe and CaNi 2 Ge 2 are discussed in terms of LMTO bond structure calculation and analysis using the Electron Localization Function (ELF). The Ge–Ge bond formation in polyanionic $^{3}_{\infty}\rm [NiGe]^{-}$ network of CaNi 2 Ge 2 can formally be regarded as oxidative coupling product of $^{2}_{\infty}\rm [NiGe]^{2-}$ layers of CaNiGe.