Ba₆Ti₅S₁₅O: A New Metal/Oxysulfide Resulting from the Inclusion of BaO into the BaTiS₃ Structure Type

From a mixture of 0.212 g BaS (1.25 mmol), 0.038 g BaO (0.25 mmol), 0.060 g Ti (1.25 mmol), and 0.080 g S (2.50 mmol) heated in a quartz tube at 700 °C for 8 days, we have synthesized Ba₆Ti₅S₁₅O. The compound crystallizes in the C222₁ space group (No. 20) with a = 6.708(5) Á, b = 15.683(4) Å, c = 23.740(7) Å, and V = 2497(2) Å3 final (R/Rw = 3.8%/5.4%). The structure is two-dimensional and features [Ti₅S₁₅O] fragments composed of five face-sharing Ti centered octahedra with O atoms occupying one site on each terminal face. These fragments are then joined together through linear bridges at the O atom and one S atom of the terminal face into the 2D layer. The Ba²⁺ cations reside in intralayer cavities, leaving the space between the layers open. Diffuse reflectance measurements show an absorption edge at approximately 1.04 eV, indicating semiconducting behavior.