Synthesis, crystal structure, and physical properties of the monoclinic form of the R4Mo4O11 compounds (R=Yb and Lu) containing infinite chains of trans-edge-shared octahedral clusters

Polycrystalline samples and single crystals of the R₄Mo₄O₁₁ compounds (R=Yb and Lu) were synthesized by solid-state reactions at high temperature in sealed Mo crucibles. The structure of Lu₄Mo₄O₁₁ (a=10.5611(1), b=5.61930(5), c=15.6877 (2), β=99.5131(4) and Z=4) was determined by single crystal X-ray diffraction and refined by least squares on F² converging to R₁=0.0425, wR₂=0.0980 for 3508 intensities. Contrary to the R₄Mo₄O₁₁ compounds with lighter rare earths, which crystallize in the orthorhombic space group Pbam, the Yb and Lu compounds crystallize in the monoclinic space group P2/m. The R₄Mo₄O₁₁ compounds contain distorted infinite oxide-molybdenum chains of trans-edge-sharing Mo₆ octahedra diluted with the rare earths. Magnetic susceptibility measurements indicate that the oxidation state of the Yb atoms is +3, affording 14 metallic valence electrons per Mo₄ fragment and, the absence of localized moments on the Mo network. Resistivity measurements on single crystals show that the Yb₄Mo₄O₁₁ and Lu₄Mo₄O₁₁ compounds are small band-gap semi-conductors.