Synthesis and structures of the quaternary sulfides KGaSnS₄, KInGeS₄, and KGaGeS₄

The new quaternary compounds KGaSnS₄, KInGeS₄, and KGaGeS₄ have been synthesized by the reaction of K₂S₅ with elemental Ga or In, Sn or Ge, and S at 900°C. The crystal structures of the three compounds have been determined by single-crystal X-ray diffraction techniques. Crystal data: KGaSnS₄-space group P1, Z = 4, a = 7.152(2), b = 7.847(2), and c = 15.163(3) Å, α = 83.78(2)°, β = 87.21(2)°, γ = 63.83(2)° (T = 153 K), R(F²) = 0.147 for 3068 observations and 130 variables, R(F) = 0.073 for 2432 observations having F²_o > 3σ(F²_o); KInGeS₄-space group P1, Z = 4, a = 7.200(5), b = 7.739(5), and c = 15.037(10) Å, α = 91.83(3)°, β = 99.26(4)°, γ = 112.01(4)° (T = 294 K), R(F²) = 0.124 for 4832 observations and 131 variables, R(F) = 0.048 for 1956 observations having F²_o > 3σ(F²_o); KGaGeS₄-space group P2₁ a, Z = 4, a = 6.853(2), b = 15.956(5), and c = 7.108(2) Å, β = 111.95(1)° (T = 115 K), R(F²) = 0.060 for 2235 observations and 65 variables, R(F) = 0.027 for 1925 observations having F²_o > 3σ(F²_o). While the three crystal structures differ, they show close similarities. All three structures are made up of layers of metal-centered tetrahedra separated by potassium ions. The main group metal atoms are disordered to varying degrees among the tetrahedra. In each structure the tetrahedra form corner-sharing chains along the a axis and these chains are connected by pairs of edge-sharing tetrahedra. The layers in KInGeS₄ and KGaGeS₄ have the same structure while that in KGaSnS₄ is different, owing to the different ways the edge-sharing tetrahedral pairs connect the chains. All three compounds are poor conductors.