Synthesis and Characterization of the Ternary Thiobismuthates A9Bi13S24 (A = K,Rb)

Ternary alkali metal thiobismuthates A₉Bi₁₃S₂₄ (A = K, Rb) were synthesized by direct combination reactions at 650 °C. The compounds crystallize in the monoclinic space group C2/m (no. 12) with cell parameters a = 30.919(1) Å, b = 4.1008(2) Å, c = 20.9072(9) Å, β = 105.826(3)° for K₉Bi₁₃S₂₄ ( 1 ) and a = 31.823(6) Å, b = 4.1177(8) Å, c = 21.086(4) Å, β = 105.62(3)° for Rb₉Bi₁₃S₂₄ ( 2 ). The crystal structure of 1 contains a 3D K₂Bi₁₃S₂₄]^7– polyanionic framework, whereas 2 consists of 2D RbBi₁₃S₂₄]^8– polyanionic slabs stacked along 201]. Both 1 and 2 are semiconductors with a band gap of 1.4 and 1.3 eV, respectively, which is supported by an electronic structure calculation. 1 melts congruently at 580 °C, while 2 melts incongruently at 575 °C. 1 and 2 are airstable and insoluble in water and organic solvents.