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

Journal Article · Wed Dec 15 04:00:00 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, Journal Name: Journal of Solid State Chemistry Journal Issue: 12 Vol. 183; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL STRUCTURE
CRYSTALS
DIFFRACTION
FLUORITE
HALIDE MINERALS
HEAT TREATMENTS
IONS
LATTICE PARAMETERS
MINERALS
MOLYBDATES
MOLYBDENUM COMPOUNDS
MOLYBDENUM IONS
MOLYBDENUM OXIDES
NEUTRON DIFFRACTION
OXIDES
OXYGEN COMPOUNDS
POLYCRYSTALS
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM IONS
PRASEODYMIUM OXIDES
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
SCATTERING
SPACE GROUPS
STOICHIOMETRY
SYMMETRY GROUPS
TRANSITION ELEMENT COMPOUNDS
VALENCE
X-RAY DIFFRACTION