Synthesis, structural trends, and physical and electronic properties of the reduced molybdenum oxides R(4)Mo(4)O(11) (R = Nd-Tm and Y) containing infinite chains of trans-edge-shared octahedral clusters.
The new compounds R(4)Mo(4)O(11) (R = Y, Nd, Sm-Tm) have been synthesized as crystalline powders by solid-state reaction in a sealed molybdenum crucible at 1400 degrees C. Single crystals suitable for X-ray structure determinations and resistivity measurements were also prepared. The R(4)Mo(4)O(11) compounds crystallize in the orthorhombic space group Pbam with four formulas per unit cell. The crystal structure of these compounds is based on infinite chains of trans-edge-shared molybdenum octahedra, which are widely separated by the rare-earth cations that are in monocapped trigonal prismatic coordination of oxygen atoms. Consequently, adjacent metallic chains do not share oxygen atoms and the shortest interchain Mo-Mo distance is greater than 7 A. Within the infinite chains, a strong pairing between the apical Mo atoms occurs, leading to a pattern of alternating short and long distances between these atoms. Resistivity measurements on single crystals show that the R(4)Mo(4)O(11) compounds are small band gap semiconductors, and magnetic susceptibility studies are in agreement with the presence of R(3+) ions. In addition, antiferromagnetic orderings have also been observed for the R(4)Mo(4)O(11) compounds with R = Gd-Tm below 5 K. Theoretical calculations confirm the stabilization of the structure by the distortion and agree with the resistivity and magnetic measurements.
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Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CNRS No. 6511, Université de Rennes 1, Institut de Chimie de Rennes, Avenue du Général Leclerc, 35042 Rennes Cedex, France.
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Gautier
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Gougeon
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