AMTeS₃(A = K, Rb, Cs; M = Cu, Ag): A New Class of Compounds Based on a New Polychalcogenide Anion, TeS₃^2-

The reaction of Cu or Ag with mixed polychalcogenide flux A₂S_xTe_y, (A = K, Rb, Cs) yielded RbCuTeS₃(1), CsCuTeS₃(2), α-KAgTeS₃(3), β-KAgTeS₃(4), RbAgTeS₃(5), and CsAgTeS₃(6) possessing new structure types. Compounds 1, 4, 5, and 6 are two-dimensional and isostructural. They crystallize in the monoclinic space group P2₁/c, with a = 7.434(3) Å, b = 10.526(3) Å, c = 8.234(3) Å, β = 106.13(3)°, V = 619.0(7) ųfor 1; a = 7.340(2) Å, b = 10.647(2) Å, c = 8.504(2) Å,β= 106.46(2)°, V = 637.4(3) ųfor 4; a = 7.566(8) Å, b = 10.724(8) Å, c = 8.586(9) Å, β = 106.36(8)°, V = 668(2) ųfor 5; and a = 7.832(6) Å, b = 10.803(7) Å, c = 8.668(8) Å, β = 106.05(6)° V = 705(2) ųfor 6. The structure consists of anionic [MTeS₃]_n^n-(M = Cu or Ag) layers and charge-compensating alkali ions between the layers. Each layer is composed of tetrahedrally coordinated Cu⁺or Ag⁺centers and trigonal pyramidal TeS₃^2-units, joined together via bridging S atoms. Compound 2 is three-dimensional and crystallizes in the cubic space group P2₁3 with a = 9.107(3) Å and V = 755.4(2) ų. Its framework is composed of trigonal planar Cu⁺centers and TeS₃^2-units. Compound 3 is two-dimensional and crystallizes in the monoclinic space group P2₁n with a = 6.171(2) Å, b = 16.406(4) Å, c = 6.318(3) Å, β = 97.32(3)°, and V = 634.4(7) ų. The structure of [AgTeS₃]_nⁿ- layers is different from those of 1, 4, 5, and 6, but the TeS₃^2-units bridge Ag⁺centers by the same pattern. All compounds are found to be wide band gap semiconductors with RbCuTeS₃possessing the narrowest at 1.95 eV. Thermal analysis studies show that 3, 5, and 6 are the most stable.