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Acta Crystallogr Sect E Struct Rep Online. 2008 June 1; 64(Pt 6): i42.
Published online 2008 May 24. doi:  10.1107/S1600536808015328
PMCID: PMC2961417

The pyrochlore-type molybdate Pr1.37Ca0.63Mo2O7


Praseodymium calcium dimolybdenum hepta­oxide, Pr1.37Ca0.63Mo2O7, crystallizes in the cubic pyrochlore-type structure. In the crystal structure, MoO6 octa­hedra are linked together by common corners, forming a three-dimensional [Mo2O6] network. The Pr and Ca atoms and the remaining O atoms are located in the voids of the [Mo2O6] network. The Pr and Ca atoms are distributed statistically over the same 16c crystallographic position with site-occupancy factors of 0.684 (3) and 0.316 (3), respectively. They are surrounded by eight O atoms forming a ditrigonal scalenohedron. All atoms lie on special positions. The (Pr, Ca) and Mo atoms are, respectively in the 16c and 16d positions with An external file that holds a picture, illustration, etc.
Object name is e-64-00i42-efi2.jpg m symmetry, and the O atoms in the 48f or 8a positions with mm or An external file that holds a picture, illustration, etc.
Object name is e-64-00i42-efi3.jpg3m site symmetry, respectively.

Related literature

For related literature, see: Hubert (1974 [triangle]); Subramanian et al. (1983 [triangle]); American Chemical Society (2007 [triangle]); Gougeon et al. (2003 [triangle]); Kerihuel & Gougeon (1995 [triangle]).


Crystal data

  • Pr1.37Ca0.63Mo2O7
  • M r = 522.18
  • Cubic, An external file that holds a picture, illustration, etc.
Object name is e-64-00i42-efi4.jpg
  • a = 10.4329 (3) Å
  • V = 1135.57 (6) Å3
  • Z = 8
  • Mo Kα radiation
  • μ = 16.45 mm−1
  • T = 293 (2) K
  • 0.16 × 0.14 × 0.12 mm

Data collection

  • Nonius KappaCCD diffractometer
  • Absorption correction: analytical (de Meulenaer & Tompa, 1965 [triangle]) T min = 0.093, T max = 0.125
  • 771 measured reflections
  • 266 independent reflections
  • 167 reflections with I > 2σ(I)
  • R int = 0.053


  • R[F 2 > 2σ(F 2)] = 0.027
  • wR(F 2) = 0.086
  • S = 1.11
  • 266 reflections
  • 12 parameters
  • Δρmax = 2.51 e Å−3
  • Δρmin = −1.55 e Å−3

Data collection: COLLECT (Nonius, 1998 [triangle]); cell refinement: COLLECT; data reduction: EVALCCD (Duisenberg et al., 2003 [triangle]); program(s) used to solve structure: SIR97 (Altomare et al., 1999 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: DIAMOND (Brandenburg, 2001 [triangle]); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808015328/pk2092sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808015328/pk2092Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report


Intensity data were collected on the Nonius KappaCCD X-ray diffactometer system of the ‘Centre de diffractométrie de l’Université de Rennes I’ (

supplementary crystallographic information


An attempt to synthesize PrCaMo16O28, a compound with the PrMo8O14 type structure (Kerihuel & Gougeon, 1995), was unsuccessful, resulting in a multiphase product. However, the formation of the new compound, Pr1.37Ca0.63Mo2O7 was achieved. A survey of the literature related to the rare earth molybdates R2Mo2O7 with the database SciFinder Scholar (American Chemical Society, 2007) shows that these compounds only form for the rare-earths from Nd to Lu. To our knowledge, no quaternary molybdate pyrochlore has thus far been reported.


Single crystals of Pr1.37Ca0.63Mo2O7 were prepared from a mixture of Pr6O11 (Rhone Poulenc, 99.99%), CaMoO4, MoO3 (Cerac, 99.95%) and Mo (Plansee, 99.9999%) with the nominal composition PrCaMo16O28. Before use, Mo powder was reduced under a flow of H2 gas at 1273 K for ten hours in order to eliminate any trace of oxygen. CaMoO4 was prepared by heating a stoichiometric mixture of CaCO3 and MoO3 in an open porcelain crucible at 1073 K for 24 h. The initial mixture (ca 5 g) was cold pressed and loaded into a molybdenum crucible, which was sealed under a low argon pressure using an arc welding system. The charge was heated at a rate of 300 K/h up to 2223 K, and the temperature was held for 5 min., then cooled at 100 K/h to 1373 K and finally furnace cooled. The final product was multiphasic with Pr1.37Ca0.63Mo2O7 and Pr1 - xCaxMo10O16, isomorphous with the RMo5O8 compounds (R = La to Gd; Gougeon et al., 2003), as predominant phases. The crystals thus obtained were of irregular shape.


The structure was solved by direct methods using SIR97 (Altomare et al., 1999). The second setting, with the origin at 3 m of the Fd3m space group, was chosen. Initial refinement with full occupancy for the Pr1 site resulted in an R factor of about 0.30. Refinement of the site-occupancy factor of the Pr1 atoms lowered the R factor to 0.0274 with an occupation factor of 0.74. As qualitative microanalyses using a Jeol JSM-35 CF scanning electron microscope equipped with a Tracor energy-dispersive-type X-ray spectrometer indicated the presence of calcium in the crystals, we surmised that the deficiency observed on the Pr1 site resulted from the presence of calcium. Refinements taking into account an occupation of the deficient Pr1 site simultaneously by Pr and Ca atoms with no constraint on the site-occupancy factors of the Pr1 and Ca1 atoms led to an over-occupation of the 16 d position. Consequently, the sum of the site occupancy factors was constrained to unity, and the ADPs of the Pr1 and Ca1 atoms were constrained to be equal. Refinement of the occupancy factor of the O2 atom in 8a position which frequently exhibits partial or total deficiency, indicates full occupation of this position.


Fig. 1.
: View of Pr1.37Ca0.63Mo2O7 along the [110] direction. Displacement ellipsoids are drawn at the 97% probability level.

Crystal data

Pr1.37Ca0.63Mo2O7Z = 8
Mr = 522.18F000 = 1867.4
Cubic, Fd3mDx = 6.109 Mg m3
Hall symbol: -F 4vw 2vwMo Kα radiation λ = 0.71070 Å
a = 10.4329 (3) ÅCell parameters from 1172 reflections
b = 10.4329 (3) Åθ = 3.4–45.3º
c = 10.4329 (3) ŵ = 16.45 mm1
α = 90ºT = 293 (2) K
β = 90ºIrregular block, black
γ = 90º0.16 × 0.14 × 0.12 mm
V = 1135.57 (6) Å3

Data collection

Nonius KappaCCD diffractometer266 independent reflections
Radiation source: fine-focus sealed tube167 reflections with I > 2σ(I)
Monochromator: horizontally mounted graphite crystalRint = 0.053
Detector resolution: 9 pixels mm-1θmax = 45.3º
T = 293(2) Kθmin = 3.4º
[var phi] scans (κ = 0) + additional ω scansh = 1→20
Absorption correction: analytical(de Meulenaer & Tompa, 1965)k = 0→14
Tmin = 0.093, Tmax = 0.125l = 0→13
771 measured reflections


Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: full  w = 1/[σ2(Fo2) + (0.0207P)2 + 4.885P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.027(Δ/σ)max < 0.001
wR(F2) = 0.086Δρmax = 2.51 e Å3
S = 1.12Δρmin = −1.55 e Å3
266 reflectionsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
12 parametersExtinction coefficient: 0.00256 (19)
Primary atom site location: structure-invariant direct methods

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/UeqOcc. (<1)
Pr10.00000.00000.00000.00947 (18)0.685 (3)
Ca10.00000.00000.00000.00947 (18)0.315 (3)
Mo10.50000.50000.50000.00539 (19)
O10.4247 (3)0.12500.12500.0160 (5)
O20.12500.12500.12500.0100 (8)

Atomic displacement parameters (Å2)

Pr10.00947 (18)0.00947 (18)0.00947 (18)−0.00154 (5)−0.00154 (5)−0.00154 (5)
Ca10.00947 (18)0.00947 (18)0.00947 (18)−0.00154 (5)−0.00154 (5)−0.00154 (5)
Mo10.00539 (19)0.00539 (19)0.00539 (19)−0.00013 (5)−0.00013 (5)−0.00013 (5)
O10.0239 (14)0.0120 (6)0.0120 (6)0.0000.000−0.0026 (8)
O20.0100 (8)0.0100 (8)0.0100 (8)0.0000.0000.000

Geometric parameters (Å, °)

Pr1—O2i2.2588Mo1—Ca1xvii3.68859 (11)
Pr1—O22.2588Mo1—Ca1xviii3.68859 (11)
Pr1—O1ii2.5930 (18)Mo1—Ca1xix3.68859 (11)
Pr1—O1iii2.5930 (18)Mo1—Ca1xx3.68859 (11)
Pr1—O1iv2.5930 (18)Mo1—Ca1xxi3.68859 (11)
Pr1—O1v2.5930 (18)Mo1—Ca1xxii3.68859 (11)
Pr1—O1vi2.5930 (18)O1—Mo1xxiii2.0046 (10)
Pr1—O1vii2.5930 (18)O1—Mo1xxiv2.0046 (10)
Pr1—Pr1vii3.68859 (11)O1—Pr1vii2.5930 (18)
Pr1—Ca1viii3.68859 (11)O1—Ca1vii2.5930 (18)
Pr1—Ca1ix3.68859 (11)O1—Ca1xxv2.5930 (18)
Pr1—Ca1x3.68859 (11)O1—Pr1xxv2.5930 (18)
Mo1—O1xi2.0046 (10)O2—Ca1xxv2.2588
Mo1—O1xii2.0046 (10)O2—Pr1vii2.2588
Mo1—O1xiii2.0046 (10)O2—Pr1ix2.2588
Mo1—O1xiv2.0046 (10)O2—Pr1xxv2.2588
Mo1—O1xv2.0046 (10)O2—Ca1vii2.2588
Mo1—O1xvi2.0046 (10)O2—Ca1ix2.2588
O2i—Pr1—O2180.0O1xii—Mo1—Ca1xvii42.51 (5)
O2i—Pr1—O1ii79.93 (4)O1xiii—Mo1—Ca1xvii137.49 (5)
O2—Pr1—O1ii100.07 (4)O1xiv—Mo1—Ca1xvii90.0
O2i—Pr1—O1iii79.93 (4)O1xv—Mo1—Ca1xvii137.49 (5)
O2—Pr1—O1iii100.07 (4)O1xvi—Mo1—Ca1xvii42.51 (5)
O1ii—Pr1—O1iii117.01 (2)O1xi—Mo1—Ca1xviii42.51 (5)
O2i—Pr1—O1iv79.93 (4)O1xii—Mo1—Ca1xviii90.0
O2—Pr1—O1iv100.07 (4)O1xiii—Mo1—Ca1xviii137.49 (5)
O1ii—Pr1—O1iv117.01 (2)O1xiv—Mo1—Ca1xviii137.49 (5)
O1iii—Pr1—O1iv117.01 (2)O1xv—Mo1—Ca1xviii90.0
O2i—Pr1—O1v100.07 (4)O1xvi—Mo1—Ca1xviii42.51 (5)
O2—Pr1—O1v79.93 (4)Ca1xvii—Mo1—Ca1xviii60.0
O1ii—Pr1—O1v180.00 (8)O1xi—Mo1—Ca1xix42.51 (5)
O1iii—Pr1—O1v62.99 (2)O1xii—Mo1—Ca1xix137.49 (5)
O1iv—Pr1—O1v62.99 (2)O1xiii—Mo1—Ca1xix90.0
O2i—Pr1—O1vi100.07 (4)O1xiv—Mo1—Ca1xix137.49 (5)
O2—Pr1—O1vi79.93 (4)O1xv—Mo1—Ca1xix42.51 (5)
O1ii—Pr1—O1vi62.99 (2)O1xvi—Mo1—Ca1xix90.0
O1iii—Pr1—O1vi180.00 (8)Ca1xvii—Mo1—Ca1xix120.0
O1iv—Pr1—O1vi62.99 (2)Ca1xviii—Mo1—Ca1xix60.0
O1v—Pr1—O1vi117.01 (2)O1xi—Mo1—Ca1xx137.49 (5)
O2i—Pr1—O1vii100.07 (4)O1xii—Mo1—Ca1xx90.0
O2—Pr1—O1vii79.93 (4)O1xiii—Mo1—Ca1xx42.51 (5)
O1ii—Pr1—O1vii62.99 (2)O1xiv—Mo1—Ca1xx42.51 (5)
O1iii—Pr1—O1vii62.99 (2)O1xv—Mo1—Ca1xx90.0
O1iv—Pr1—O1vii180.00 (8)O1xvi—Mo1—Ca1xx137.49 (5)
O1v—Pr1—O1vii117.01 (2)Ca1xvii—Mo1—Ca1xx120.0
O1vi—Pr1—O1vii117.01 (2)Ca1xviii—Mo1—Ca1xx180.0
O1ii—Pr1—Pr1vii135.34 (4)O1xii—Mo1—Ca1xxi137.49 (5)
O1iii—Pr1—Pr1vii81.87 (4)O1xiii—Mo1—Ca1xxi42.51 (5)
O1iv—Pr1—Pr1vii81.87 (4)O1xiv—Mo1—Ca1xxi90.0
O1v—Pr1—Pr1vii44.66 (4)O1xv—Mo1—Ca1xxi42.51 (5)
O1vi—Pr1—Pr1vii98.13 (4)O1xvi—Mo1—Ca1xxi137.49 (5)
O1vii—Pr1—Pr1vii98.13 (4)Ca1xvii—Mo1—Ca1xxi180.0
O1ii—Pr1—Ca1viii44.66 (4)Ca1xx—Mo1—Ca1xxi60.0
O1iii—Pr1—Ca1viii98.13 (4)O1xi—Mo1—Ca1xxii137.49 (5)
O1iv—Pr1—Ca1viii98.13 (4)O1xii—Mo1—Ca1xxii42.51 (5)
O1v—Pr1—Ca1viii135.34 (4)O1xiii—Mo1—Ca1xxii90.0
O1vi—Pr1—Ca1viii81.87 (4)O1xiv—Mo1—Ca1xxii42.51 (5)
O1vii—Pr1—Ca1viii81.87 (4)O1xv—Mo1—Ca1xxii137.49 (5)
O1ii—Pr1—Ca1ix81.87 (4)Ca1xix—Mo1—Ca1xxii180.0
O1iii—Pr1—Ca1ix81.87 (4)Ca1xx—Mo1—Ca1xxii60.0
O1iv—Pr1—Ca1ix135.34 (4)Ca1xxi—Mo1—Ca1xxii120.0
O1v—Pr1—Ca1ix98.13 (4)Mo1xxiii—O1—Mo1xxiv133.86 (14)
O1vi—Pr1—Ca1ix98.13 (4)Mo1xxiii—O1—Pr1vii105.99 (3)
O1vii—Pr1—Ca1ix44.66 (4)Mo1xxiv—O1—Pr1vii105.99 (3)
Pr1vii—Pr1—Ca1ix60.0Mo1xxiii—O1—Ca1vii105.99 (3)
Ca1viii—Pr1—Ca1ix120.0Mo1xxiv—O1—Ca1vii105.99 (3)
O2i—Pr1—Ca1x35.3Mo1xxiii—O1—Ca1xxv105.99 (3)
O2—Pr1—Ca1x144.7Mo1xxiv—O1—Ca1xxv105.99 (3)
O1ii—Pr1—Ca1x98.13 (4)Pr1vii—O1—Ca1xxv90.68 (8)
O1iii—Pr1—Ca1x98.13 (4)Ca1vii—O1—Ca1xxv90.68 (8)
O1iv—Pr1—Ca1x44.66 (4)Mo1xxiii—O1—Pr1xxv105.99 (3)
O1v—Pr1—Ca1x81.87 (4)Mo1xxiv—O1—Pr1xxv105.99 (3)
O1vi—Pr1—Ca1x81.87 (4)Pr1vii—O1—Pr1xxv90.68 (8)
O1vii—Pr1—Ca1x135.34 (4)Ca1vii—O1—Pr1xxv90.68 (8)
O1xi—Mo1—O1xii94.97 (9)Pr1—O2—Pr1ix109.5
O1xi—Mo1—O1xiii94.97 (9)Ca1xxv—O2—Pr1ix109.5
O1xii—Mo1—O1xiii94.97 (9)Pr1vii—O2—Pr1ix109.5
O1xii—Mo1—O1xiv85.03 (9)Pr1vii—O2—Pr1xxv109.5
O1xiii—Mo1—O1xiv85.03 (9)Pr1ix—O2—Pr1xxv109.5
O1xi—Mo1—O1xv85.03 (9)Pr1—O2—Ca1vii109.5
O1xiii—Mo1—O1xv85.03 (9)Pr1ix—O2—Ca1vii109.5
O1xiv—Mo1—O1xv94.97 (9)Pr1xxv—O2—Ca1vii109.5
O1xi—Mo1—O1xvi85.03 (9)Pr1—O2—Ca1ix109.5
O1xii—Mo1—O1xvi85.03 (9)Ca1xxv—O2—Ca1ix109.5
O1xiv—Mo1—O1xvi94.97 (9)Pr1xxv—O2—Ca1ix109.5
O1xv—Mo1—O1xvi94.97 (9)Ca1vii—O2—Ca1ix109.5

Symmetry codes: (i) −x, −y, −z; (ii) −y, z−1/4, x−1/4; (iii) z−1/4, x−1/4, −y; (iv) x−1/4, y−1/4, −z; (v) y, −z+1/4, −x+1/4; (vi) −z+1/4, −x+1/4, y; (vii) −x+1/4, −y+1/4, z; (viii) −x−1/4, −y−1/4, z; (ix) x, −y+1/4, −z+1/4; (x) x, −y−1/4, −z−1/4; (xi) −y+1/2, −z+1/2, −x+1; (xii) −z+1/2, −x+1, −y+1/2; (xiii) −x+1, −y+1/2, −z+1/2; (xiv) y+1/2, z+1/2, x; (xv) z+1/2, x, y+1/2; (xvi) x, y+1/2, z+1/2; (xvii) −x+1/4, −y+3/4, z+1/2; (xviii) y+1/4, −x+1/2, z+3/4; (xix) x+1/2, −y+1/4, −z+3/4; (xx) y+3/4, −x+1/2, z+1/4; (xxi) −x+3/4, −y+1/4, z+1/2; (xxii) x+1/2, −y+3/4, −z+1/4; (xxiii) x, −y+3/4, −z+3/4; (xxiv) x, y−1/2, z−1/2; (xxv) y+1/4, −x, z+1/4.


Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: PK2092).


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