Structure and Chemical Bonding of Binary Ytterbium Germanides, Yb₃Ge₅ and YbGe₃, Prepared by High-Pressure and High-Temperature Reactions

Two new ytterbium germanides, Yb 3 Ge 5 and YbGe 3, were obtained using high-pressure and high-temperature reactions. Yb 3 Ge 5 crystallizes in the Pu 3 Pd 5 structure (the space group Cmcm, No. 63) with a = 9.3739(8) Ǻ, b = 7.5569(5) Ǻ, c = 9.5170(8) Ǻ, and V = 674.16(9) Ǻ 3 . It is a new polymorph and contains Ge 5 units with a square-pyramidal structure. COHP and ELF calculations revealed that the unit is constructed with strong Ge–Ge covalent bonds. The XAS analysis showed that the mean oxidation state of Yb is +2.4. It is metallic and is an example of electron-rich Zintl phases. YbGe 3 crystallizes in the Cu 3 Au structure (the space group Pm3̅m, No. 221) having a unit cell of a = 4.276(1) Ǻ and V = 78.13(3) Ǻ 3 . It is the first example for heavy rare-earth germanides having the Cu 3 Au-type structure. The mean oxidation state of Yb is +2.4. YbGe 3 is metallic and is possibly a valence-fluctuating system.