Synthesis and Structural Characterization of Ba7Li11Bi10 and AE4(Li,Tr)7Pn6 (AE = Sr, Ba, Eu; Tr = Ga, In; Pn = Sb, Bi)

Abstract

Reported are the synthesis and crystal structure of Ba₇Li₁₁Bi₁₀, a new ternary compound crystallizing in its own type with the monoclinic space group C2/m (a = 18.407(3) Å, b = 5.0258(9) Å, and c = 18.353(3) Å; β = 104.43(1)°; Pearson symbol mS56), and those of the structurally related quaternary phases Ba₄(Li_1−xGa_x)₇Sb₆, Ba₄(Li_1−xIn_x)₇Sb₆, Ba₄(Li_1−xIn_x)₇Bi₆, and Eu₄(Li_1−xIn_x)₇Bi₆ (crystallizing in the Eu₄Li₇Bi₆ structure type with the same monoclinic space group C2/m (a = 18.4045(13)–17.642(4) Å, b = 5.012(4)–4.8297(10) Å, and c = 13.2792(10)–12.850(3) Å, β = 126.80(1)–125.85(1)°; Pearson symbol mS34). All studied compounds are identified among the products of the high-temperature reactions of the corresponding elements. Both types of crystal structures are based on corner- and edge-linked Li-centered Sb₄ (or Bi₄) tetrahedra, Sb₆ (or Bi₆) octahedra, and Sb₂ or Bi₂ dumbbells. Given the similarities between the two structures, it might be proposed that they represent the simplest members of a potentially large homologous series described with the general formulae (BaLi₃Sb₂)_n(Ba₃Li₄Sb₄)_m or (BaLi₃Bi₂)_n(Ba₃Li₄Bi₄)_m, where the more complicated “7-11-10” phase is the member with n = 2 and m = 1, while the “4-7-6” one is the intergrowth of the two components in an equal ratio. The computed electronic band structures of Ba₇Li₁₁Bi₁₀ and idealized Ba₄Li₇Bi₆ (a model for Ba₄(Li_1−xIn_x)₇Bi₆) are also discussed.