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

Two new ytterbium germanides, Yb₃Ge₅ and YbGe₃, were obtained using high-pressure and high-temperature reactions. Yb₃Ge₅ crystallizes in the Pu₃Pd₅ structure (the space group <i>Cmcm</i>, No. 63) with <i>a</i> = 9.3739(8) Ǻ, <i>b</i> = 7.5569(5) Ǻ, <i>c</i> = 9.5170(8) Ǻ, and <i>V</i> = 674.16(9) Ǻ³. It is a new polymorph and contains Ge₅ 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. YbGe₃ crystallizes in the Cu₃Au structure (the space group <i>Pm3̅m</i>, No. 221) having a unit cell of <i>a</i> = 4.276(1) Ǻ and <i>V</i> = 78.13(3) Ǻ³. It is the first example for heavy rare-earth germanides having the Cu₃Au-type structure. The mean oxidation state of Yb is +2.4. YbGe₃ is metallic and is possibly a valence-fluctuating system