Synthesis, crystal structure, and physical properties of the monoclinic form of the R4Mo 4O 11 compounds ( R=Yb and Lu) containing infinite chains of trans-edge-shared octahedral clusters

Abstract

Polycrystalline samples and single crystals of the R 4Mo 4O 11 compounds ( R=Yb and Lu) were synthesized by solid-state reactions at high temperature in sealed Mo crucibles. The structure of Lu 4Mo 4O 11 ( 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 F 2 converging to R 1=0.0425, w R 2=0.0980 for 3508 intensities. Contrary to the R 4Mo 4O 11 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 R 4Mo 4O 11 compounds contain distorted infinite oxide-molybdenum chains of trans-edge-sharing Mo 6 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 Mo 4 fragment and, the absence of localized moments on the Mo network. Resistivity measurements on single crystals show that the Yb 4Mo 4O 11 and Lu 4Mo 4O 11 compounds are small band-gap semi-conductors.