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Title: Preparation and structural study from neutron diffraction data of Pr{sub 5}Mo{sub 3}O{sub 16}

The title compound has been prepared as polycrystalline powder by thermal treatments of mixtures of Pr{sub 6}O{sub 11} and MoO{sub 2} in air. In the literature, an oxide with a composition Pr{sub 2}MoO{sub 6} has been formerly described to present interesting catalytic properties, but its true stoichiometry and crystal structure are reported here for the first time. It is cubic, isostructural with CdTm{sub 4}Mo{sub 3}O{sub 16} (space group Pn-3n, Z=8), with a=11.0897(1) A. The structure contains MoO{sub 4} tetrahedral units, with Mo-O distances of 1.788(2) A, fully long-range ordered with PrO{sub 8} polyhedra; in fact it can be considered as a superstructure of fluorite (M{sub 8}O{sub 16}), containing 32 MO{sub 2} fluorite formulae per unit cell, with a lattice parameter related to that of cubic fluorite (a{sub f}=5.5 A) as a{approx}2a{sub f}. A bond valence study indicates that Mo exhibits a mixed oxidation state between 5+ and 6+ (perhaps accounting for the excellent catalytic properties). One kind of Pr atoms is trivalent whereas the second presents a mixed Pr{sup 3+}-Pr{sup 4+} oxidation state. The similarity of the XRD pattern with that published for Ce{sub 2}MoO{sub 6} suggests that this compound also belongs to the same structural type, with an actualmore » stoichiometry Ce{sub 5}Mo{sub 3}O{sub 16}. -- Graphical Abstract: Formerly formulated as Pr{sub 2}MoO{sub 6}, the title compound is a cubic superstructure of fluorite (a=11.0897(1) A, space group Pn-3n) due to the long-range ordering of PrO{sub 8} scalenohedra and MoO{sub 4} tetrahedral units, showing noticeable shifts of the oxygen positions in order to provide a tetrahedral coordination for Mo ions. A mixed valence Mo{sup 5+}-Mo{sup 6+} is identified, which could account for the excellent catalytic properties of this material. Display Omitted« less
Authors:
 [1] ;  [1] ; ;  [2]
  1. Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Cantoblanco, E-28049 Madrid, Spain. (Spain)
  2. Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland)
Publication Date:
OSTI Identifier:
21494154
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 183; Journal Issue: 12; Other Information: DOI: 10.1016/j.jssc.2010.10.015; PII: S0022-4596(10)00469-X; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CRYSTAL STRUCTURE; FLUORITE; HEAT TREATMENTS; LATTICE PARAMETERS; MOLYBDATES; MOLYBDENUM IONS; MOLYBDENUM OXIDES; NEUTRON DIFFRACTION; POLYCRYSTALS; PRASEODYMIUM IONS; PRASEODYMIUM OXIDES; SPACE GROUPS; STOICHIOMETRY; VALENCE; X-RAY DIFFRACTION CHALCOGENIDES; CHARGED PARTICLES; COHERENT SCATTERING; CRYSTALS; DIFFRACTION; HALIDE MINERALS; IONS; MINERALS; MOLYBDENUM COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; PRASEODYMIUM COMPOUNDS; RARE EARTH COMPOUNDS; REFRACTORY METAL COMPOUNDS; SCATTERING; SYMMETRY GROUPS; TRANSITION ELEMENT COMPOUNDS