Crystal and electronic structure of a quaternary layered compound from the k-in-ge-sb system: K₉in₉gesb₂₂

The quaternary Zintl phase material, K₉In₉GeSb₂₂ (1), has been prepared at 650°C and its structure determined by single crystal X-ray diffraction: triclinic, space group P1̄ with a = 11.62 (1) Å, b = 13.04 (3) Å, c = 11.27 (2) Å, α = 113.5 (2)°, β = 91.7 (1)°, γ = 112.3 (1)°, V = 1415 (4) ų, and D_calcd = 4.851 g/cm³ for Z = 2 and R(R_W) = 7.9% (8.8%). Antimonide 1 contains layers comprised of indium, germanium, and arsenic separated by K⁺ cations. The In-Ge-Sb layers in 1 contain In_(2-x)Ge_xSb₆ (x ≅ 1) dimers with In(Ge)-In(Ge) bonds, InSb₄ tetrahedra, and Sb₃ trimers, as well as infinite chains with Sb-Sb bonds. There is an unusual metal-metal bonded site in 1, that contains contains a solid solution of 1:1 In and Ge, with an In(Ge)-In(Ge) separation of 2.659 (1) Å. The nature of this experimentally determined solid solution at the M-M bonded site, and its effects on the electronic structure of K₉In₉GeSb₂₂, was investigated via tight binding calculations.