Synthesis, Crystal Structure, and Electronic Structure of a Binary-Ordered Phase Mn₁₆Ge₇

A new binary phase, Mn₁₆Ge₇, has been identified in the Mn-rich region of the Mn-Ge binary system alongside the ζ phase (ζ₁-Mn₂₃Ge₉ + ζ₂-Mn₅Ge₂) via high-temperature synthesis. Their crystal structures have been determined by single-crystal X-ray diffraction studies. The compound Mn₁₆Ge₇ crystallizes in the monoclinic crystal system with the space group C2/m (a ≈ 10.61 Å, b ≈ 7.77 Å, c ≈ 8.16 Å, and β ≈ 111.72°; Pearson code: mC46). The structure contains ten independent crystallographic sites in the unit cell in which seven are manganese and three are germanium sites. The ζ phase consists of two structurally related microsyntactic intergrowth phases (ζ₁-Mn₂₃Ge₉ and ζ₂-Mn₅Ge₂); both crystallize in the trigonal space group P3c1 (a ≈ 7.17 Å, c ≈ 39.06 Å for ζ₁-Mn₂₃Ge₉ and a ≈ 7.17 Å, c ≈ 13.00 Å for ζ₂-Mn₅Ge₂) but slightly differ in stoichiometry. Electronic structure calculations of Mn₁₆Ge₇ suggest that the most stable configuration is obtained for the model with the shortest Mn-Mn contacts with antiferromagnetic coupling, while longer Mn-Mn separations typically promote ferromagnetic alignment. The band structure shows that the compound is metallic, and bonding analysis indicates that Mn-Mn homoatomic interactions play a crucial role in the stability of the compound.