Synthesis and Structural Analysis of Sr_5.8La_4.4Ti_7.8S₂₄O₄ and La₁₄Ti₈S₃₃O₄:  Two New Oxysulfides Containing a Common [(Ti₄S₂O₄)(TiS₆)_4/2]^12- Layer

Two new titanium oxysulfides Sr_5.8La_4.4Ti_7.8S₂₄O₄ and La₁₄Ti₈S₃₃O₄ were prepared by high-temperature methods (925−950 °C; ∼ 90−104 h) from stoichiometric ratios of SrS, La₂S₃, Ti, S, and TiO₂ or La₂O₃ (or SrO for Sr_5.8La_4.4Ti_7.8S₂₄O₄) oxygen sources. The sample crystallinity and purity was greatly enhanced when LaCl₃ fluxes were employed. The compounds were characterized by single-crystal and powder (Rietveld profile analysis) X-ray diffraction studies and EDX analysis. Both compounds are black insulators (all Ti⁴⁺) and contain a common [(Ti₄S₂O₄)(TiS₆)_4/2]^-12 layer despite the difference in composition and crystal symmetry. For La₁₄Ti₈S₃₃O₄, these layers are separated by TiS₆ octahedra and 8- and 9-coordinate La−S polyhedra. For Sr_5.8La_4.4Ti_7.8S₂₄O₄, the layers are separated by a TiS₆ octahedron and two disordered Ti₁_-<i>_x</i>Sr<i>_x</i>S₆ octahedra. La and Sr are also disordered on an interlayer nine-coordinate site. Crystal data (153 K):  Sr_5.8La_4.4Ti_7.8S₂₄O₄, tetragonal, space group <i>P</i>4/<i>mmm</i> <i>a</i> = 10.569(3), <i>c</i> = 8.516(4) Å, <i>V</i> = 951.4(5) ų, <i>Z</i> = 1, <i>R(F)</i> = 4.28%, and <i>R</i>_w<i>(F</i><i>²</i><i>)</i> = 10.39%. For La₁₄Ti₈S₃₃O₄, monoclinic, space group <i>C</i>2/<i>m</i>, <i>a</i> = 14.904(1) , <i>b</i> = 14.736(1), <i>c</i> = 12.278(1) Å, β = 112.773(5)°, <i>V</i> = 2486.2(3) ų, <i>Z</i> = 2, <i>R(F)</i> = 3.92%, and <i>R</i>_w<i>(F</i><i>²</i><i>)</i> = 10.00%.