Synthesis and Characterization of Novel One-Dimensional Phases from Supercritical Ammonia: Cs3Ag2Sb3S8, α- and β-Cs2AgSbS4, and Cs2AgAsS4
journal contributionposted on 14.03.1996, 00:00 by Paul T. Wood, George L. Schimek, Joseph W. Kolis
Synthetic efforts utilizing Cs2CO3, Ag, M2S3 (M = As, Sb), and S8 in supercritical ammonia (160 °C) have yielded four novel, one-dimensional compounds in the Cs−Ag−M−S system. These members were characterized by single-crystal X-ray diffraction and diffuse reflectance measurements. Cs3Ag2Sb3S8 (I) crystallizes in the monoclinic space group P21/m with lattice parameters of a = 10.539(3) Å, b = 7.234 (3) Å, c = 12.777 (3) Å, β = 101.96 (2)°, V = 952.7(9) Å3, z = 2, and R = 0.0377 (wR = 0.0445). The columnar framework of this compound consists of [SbS2]∞- chains and SbS43- tetrahedra that are stitched together by Ag(I) ions. When the Cs/Sb ratio is doubled, α- and β-Cs2AgSbS4 (II and III, respectively) are obtained. Both phases contain identical anionic chains which pack in different ways. Compound II crystallizes in the monoclinic space group P21/c with a = 6.848(3) Å, b = 11.413(3) Å, c = 13.187(3) Å, β = 102.45(3)°, V = 1006.5(6) Å3, z = 4, and R = 0.0414 (wR = 0.0498). Compound III was refined in the triclinic space group P1̄ with a = 6.917(2) Å, b = 7.341(2) Å, c = 10.998(2) Å, α = 73.83(2)°, β = 76.08(2)°, γ = 71.71(2)°, V = 502.0(2) Å3, z = 2, and R = 0.0343 (wR = 0.0423). Compound IV, the isostructural arsenic analog of III, Cs2AgAsS4, has also been prepared and structured: a = 6.783(2) Å, b = 7.191(2) Å, c = 11.088(2) Å, α = 73.61(3)°, β = 75.10(3)°, γ = 70.83(3)°, V = 481.9(2) Å3, z = 2, and R = 0.0397 (wR = 0.0601). The infinite, one-dimensional anionic chains in the Cs2AgMS4 phases are built from isolated MS43- tetrahedra (M = As, Sb) joined by Ag(I) ions. In all four materials the silver atoms are tetrahedrally coordinated by sulfur atoms, and cesium(I) cations are located in the surrounding voids. Bond valence sums support the electron precise counts predicted for all three members: Cs3IAg2ISb2IIISbVS8-II and Cs2IAgIMVS4-II. Optical bandgaps determined via diffuse reflectance measurements indicate that these are wide bandgap materials (2.1−2.7eV) and thus are in agreement with the expected electronic configurations.