Polysulfide Ligands in Solid-State Antimony Compounds. Isolation and Structural Characterization of Cs₂Sb₄S₈ and CsSbS₆

Cs₂Sb₄S₈ and CsSbS₆ were synthesized by reacting Sb with a Cs₂S_x flux. An investigation of the Sb/Cs₂S_x system at 260 and 280 °C revealed the presence of two new ternary sulfides, Cs₂Sb₄S₈ (I) (67% yield) and CsSbS₆ (II) (69% yield), respectively. Red-orange Cs₂Sb₄S₈ crystallizes in the triclinic [formula omited] space group (No. 2) with a = 6.743(1) Å, b = 9.577(2) Å, c = 6.397(1) Å, α = 91.63(1)°, β= 104.83(1)°, γ = 80.57(1)°, V= 392 ų, Z = 1, and d_calc = 4.27g/cm³; number of data with F₀² > 3σ(F₀²) 1889, number of variables 65, 2θ_max = 60°. The final R/R_w = 3.2/4.9. The structure of I consists of [Sb₄S₆] units that are assembled into chains in the a direction. The chains are connected by S₂² bridging units to form layers that are parallel to the (011) crystallographic plane. The layers are connected by Sb-S interactions to form channels that are filled with 10-coordinate C^s+ ions (Cs-S mean = 3.62(4) Å). Compound II crystallizes in the P2₁/n space group (No. 14) with a = 5.885(2) Å, b = 14.413(2) Å, c = 11.079(2) Å, β = 101.69(2)°, V = 920 ų, Z = 4, and d_calc = 3.23g/cm³; number of data with F₀² > 3σ(F₀²) 1926, number of variables 74, 2θ_max = 60°. The final R/R_w = 2.5/3.9. The structure consists of four-membered Sb₂S₂ rings linked along the a axis via pentasulfide ligands to form one-dimensional chains that are separated by C^s+ ions. The band gaps of the semiconducting I and II are 2.05 and 2.25 eV, respectively. Thermal analysis data for I and II are reported.