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

Journal Article · Wed Dec 15 00:00:00 EST 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2010.10.015· OSTI ID:21494154

Martinez-Lope, M J ^[1]; Sheptyakov, D; Pomjakushin, V ^[2]

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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)

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 actual 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

• OSTI ID: 21494154
• Journal Information: Journal of Solid State Chemistry, Vol. 183, 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.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

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