La3TWS3O6 (T = Cr, Mn, Fe, Co, Ni): Quinary Rare Earth Transition-Metal Compounds Showing a Nonmagnetic/Magnetic Transition (T = Co) - Synthesis, Structure and Physical Properties

The title compounds were synthesized from La2O3, T (T = Cr, Mn, Fe, Co, Ni), sulfur, tungsten and WO3 under vacuum at 950 degrees C. They crystallize in the space group P6(3)/m (No. 176). The lattice constants for the chromium compound are a = 9.442(2) angstrom and c = 5.506(2) angstrom. Those for the other compounds are similar. The electron partition of (La3+)(3)T3+W6+(S2-)(3)(O2-)(6) indicates that the transition metals in this structure all have a 3(+) oxidation state and the solid is a normal valence Compound. Ill this Structure, the TS6/2 octahedra form chains parallel to the c axis by sharing faces. In the chromium compound, the Cr-Cr distance in the octahedron chain is 2.7531 angstrom, The tungsten atoms ill the structure are at the centers of O-6 trigonal prisms, whereas lanthanum atoms form trigonal prisms enclosing the tungsten atoms. Resistivity and Susceptibility measurements reveal the insulating nature and nonmagnetic to magnetic transition of the cobalt compound.