Synthesis and characterization of the new rare-earth/transition-metal oxysulfides La₆Ti₂S₈O₅ and La₄Ti₃S₄O₈

The new compounds La₆Ti₂S₈O₅ and La₄Ti₃S₄O₈ have been prepared from the reaction of La₂S₃ with TiO₂. Both phases are highly resistive and weakly paramagnetic. Single-crystal X-ray diffraction measurements show that La₆Ti₂S₈O₅ crystallizes in space group C²_2h -P2₁/m of the monoclinic system with two formula units in a cell of dimensions a = 12.572(10), b = 4.053(2), c = 16.289(14) Å, β = 96.79(1)° (T = 113 K). The structure contains six crystallographically independent La atoms with four different coordination geometries, and Ti atoms in octahedral coordination. The Ti octahedra form an infinite, corner-sharing dimeric chain in the b direction. La₄Ti₃S₄O₈ crystallizes in the monoclinic space group C³_2h -C2/m with four formula units in a cell with dimensions a = 18.363(9), b = 3.886(2), c = 17.911(9) Å, β = 109.83(2)° (T = 113 K). The structure is composed of La atoms in tricapped trigonal prisms and Ti atoms in octahedra and highly distorted tetrahedra. There are four distinct linkages between these octahedra that include edge- and corner-shared O and S atoms.