Studied and Forgotten. A Fresh Look at the Li–Mn–Ge System

The crystal structure of the ternary germanide Li 2 MnGe has been re‐evaluated from single‐crystal X‐ray diffraction data. This compound crystallizes in a non‐centrosymmetric superstructure of the ZrCuSiAs type (space group P 4 bm , Pearson code tP 16), with the lattice parameters a = 6.088(4) Å, c = 6.323(4) Å. First‐principle calculations for the idealized structure predict antiferromagnetic exchange in the square Mn nets and semimetallic ground state. In addition, a new ternary phase with the composition Li 2– x Mn 4+ x Ge 5 ( x ≈ 1.2) was discovered. It adopts the V 6 Si 5 structure type (space group Ibam , Pearson code oI 44), with the lattice parameters a = 7.570(2) Å, b = 16.323(3) Å, c = 5.057(1) Å. DSC/TG measurements show that this compound is thermally stable below 995 K.