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Acta Cryst. (2013). E69, i7    [ doi:10.1107/S1600536813000731 ]

The defect scheelite-type lanthanum(III) ortho-oxidomolybdate(VI) La0.667[MoO4]

T. Schustereit, T. Schleid and I. Hartenbach

Abstract top

In scheelite-type La0.667[MoO4], one crystallographically unique position with site symmetry -4.. and an occupancy of 2/3 is found for the La3+ cation. The cation is surrounded by eight O atoms in the shape of a trigonal dodeca­hedron. The structure also contains one [MoO4]2- anion (site symmetry -4..), which is surrounded by eight vertex-attached La3+ cations. The polyhedra around the La3+ cations are inter­connected via common edges, building up a three-dimensional network, in the tetra­hedral voids of which the Mo6+ cations reside.

Comment top

The title compound crystallizes isotypically with the already known defect scheelite-type lanthanide ortho-oxidomolybdates(VI) with general formula Ln0.667[MoO4] (Ln = Ce, Pr, Nd, and Sm; Schustereit et al., 2011). The crystallographically unique La3+ cation at Wyckoff position 4b is surrounded by eight oxide anions in the shape of a trigonal dodecahedron (Fig. 1). Besides the lanthanum cation, the structure also contains an isolated and bisphenoidally distorted tetrahedral ortho-oxidomolybdate(VI) unit [MoO4]2–. Its central Mo6+ cation at Wyckoff position 4a exhibits the same site symmetry (4..) as the La3+ cation. Hence, in order to maintain electroneutrality, the latter shows a statistically under-occupation of 2/3 on its atomic position. The [MoO4]2– tetrahedra share common vertices with eight [LaO8]13– dodecahedra to build up the scheelite-type crystal structure (Fig. 2). The cations at the sites 4a (La3+) and 4b (Mo6+) are thereby arranged in two interpenetrating diamond-like lattices (Schustereit et al., 2011).

Related literature top

For isotypic Ln0.667[MoO4] structures with Ln = Ce, Pr, Nd and Sm, see: Schustereit et al. (2011). For synthetic details, see: Liu et al. (2012).

Experimental top

Colourless, irregular-shaped single crystals of scheelite-type La0.667[MoO4] were obtained as a by-product in an unsuccessful attempt to synthesize LaF[MoO4] according to the Pecchini method (Liu et al., 2012). Aqueous solutions with stoichiometric amounts of La(NO3)3 and (NH4)6Mo7O24 (molar ratio 7 : 1) were prepared for each compound and HF was added to the latter (molar ratio HF : (NH4)6Mo7O24 = 7 : 1). As chelating agent, citric acid (CA) was dissolved in both solutions with a molar ratio of CA : La3+ = 1 : 1 and CA : Mo6+ = 2 : 1. The pH value of the La3+-containing solution was adjusted to 3 – 4 with an aqueous ammonia solution as well as the pH value of the CA/HF/(NH4)6Mo7O24 mixture, in this case to a value of 7 – 8. The two solutions were combined, stirred, and heated for about 30 minutes to obtain a transparent solution, which was then dried at 473 K for 5 hours. The residual product was thermally treated in air at 1123 K for 12 hours.

Refinement top

The site occupation factor of the La3+ site was refined freely to a value of 0.6676 (10).

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: SCALEPACK and DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Trigonal dodecahedral oxygen environment of the La3+ cation in defect scheelite-type La0.667[MoO4]; ellipsoids are drawn at the 80 % probability level. [Symmetry codes: (i) x, y, z; (ii) –x+1/2, –y, z+1/2; (iii) –y+3/4, x+1/4, z+1/4; (iv) y+3/4, –x+3/4, z+3/4; (v) –x, –y, –z; (vi) x+1/2, y, –z+1/2; (vii) y+1/4, –x+3/4, –z+3/4; (viii) –y+1/4, x+1/4, –z+1/4].
[Figure 2] Fig. 2. View of the crystal structure of defect scheelite-type La0.667[MoO4] along [010]; the bisphenoidally distorted tetrahedral ortho-oxidomolybdate(VI) units [MoO4]2– are given in the polyhedral representation.
Lanthanum(III) ortho-tetraoxidomolybdate(VI) top
Crystal data top
La0.667[MoO4]Dx = 4.890 Mg m3
Mr = 252.59Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/aCell parameters from 1769 reflections
Hall symbol: -I 4adθ = 0.4–30.5°
a = 5.3599 (3) ŵ = 11.74 mm1
c = 11.9425 (7) ÅT = 293 K
V = 343.09 (3) Å3Irregular, colourless
Z = 40.11 × 0.08 × 0.06 mm
F(000) = 448
Data collection top
Nonius KappaCCD
260 independent reflections
Radiation source: fine-focus sealed tube174 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.046
ω and ϕ scansθmax = 30.4°, θmin = 4.2°
Absorption correction: numerical
(X-SHAPE; Stoe & Cie, 1995)
h = 77
Tmin = 0.291, Tmax = 0.480k = 77
2577 measured reflectionsl = 1616
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.016 w = 1/[σ2(Fo2) + (0.0079P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.032(Δ/σ)max < 0.001
S = 0.98Δρmax = 0.41 e Å3
260 reflectionsΔρmin = 0.37 e Å3
16 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0082 (5)
Crystal data top
La0.667[MoO4]Z = 4
Mr = 252.59Mo Kα radiation
Tetragonal, I41/aµ = 11.74 mm1
a = 5.3599 (3) ÅT = 293 K
c = 11.9425 (7) Å0.11 × 0.08 × 0.06 mm
V = 343.09 (3) Å3
Data collection top
Nonius KappaCCD
260 independent reflections
Absorption correction: numerical
(X-SHAPE; Stoe & Cie, 1995)
174 reflections with I > 2σ(I)
Tmin = 0.291, Tmax = 0.480Rint = 0.046
2577 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01616 parameters
wR(F2) = 0.0320 restraints
S = 0.98Δρmax = 0.41 e Å3
260 reflectionsΔρmin = 0.37 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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) top
xyzUiso*/UeqOcc. (<1)
La0.00000.25000.62500.01492 (18)0.6676 (10)
Mo0.00000.25000.12500.01706 (15)
O0.1374 (3)0.0106 (2)0.20490 (13)0.0313 (5)
Atomic displacement parameters (Å2) top
La0.0171 (2)0.0171 (2)0.0107 (2)0.0000.0000.000
Mo0.01534 (18)0.01534 (18)0.0205 (2)0.0000.0000.000
O0.0209 (8)0.0329 (9)0.0403 (9)0.0048 (6)0.0031 (9)0.0105 (7)
Geometric parameters (Å, º) top
La—Oi2.5728 (14)La—Lax4.0120 (2)
La—Oii2.5728 (14)La—Laxi4.0120 (2)
La—Oiii2.5728 (14)La—Laiv4.0120 (2)
La—Oiv2.5728 (14)Mo—Oxii1.7605 (14)
La—Ov2.5766 (14)Mo—Oxiii1.7605 (14)
La—Ovi2.5766 (14)Mo—Oxiv1.7605 (14)
La—Ovii2.5766 (14)Mo—O1.7606 (14)
La—Oviii2.5766 (14)O—Laiv2.5728 (14)
La—Laix4.0120 (2)O—Laxv2.5766 (14)
Oi—La—Oii128.57 (4)Oiii—La—Lax161.84 (3)
Oi—La—Oiii75.70 (7)Oiv—La—Lax66.64 (3)
Oii—La—Oiii128.57 (4)Ov—La—Lax103.20 (4)
Oi—La—Oiv128.57 (4)Ovi—La—Lax38.79 (3)
Oii—La—Oiv75.70 (7)Ovii—La—Lax129.62 (3)
Oiii—La—Oiv128.57 (4)Oviii—La—Lax85.04 (3)
Oi—La—Ov148.98 (6)Laix—La—Lax123.628 (3)
Oii—La—Ov68.24 (3)Oi—La—Laxi161.84 (3)
Oiii—La—Ov74.21 (2)Oii—La—Laxi66.64 (3)
Oiv—La—Ov77.64 (5)Oiii—La—Laxi103.00 (3)
Oi—La—Ovi74.21 (2)Oiv—La—Laxi38.85 (3)
Oii—La—Ovi77.64 (5)Ov—La—Laxi38.79 (3)
Oiii—La—Ovi148.98 (6)Ovi—La—Laxi103.20 (4)
Oiv—La—Ovi68.24 (3)Ovii—La—Laxi85.04 (3)
Ov—La—Ovi136.53 (7)Oviii—La—Laxi129.62 (3)
Oi—La—Ovii77.64 (5)Laix—La—Laxi123.628 (3)
Oii—La—Ovii148.98 (6)Lax—La—Laxi83.823 (4)
Oiii—La—Ovii68.24 (3)Oi—La—Laiv38.85 (3)
Oiv—La—Ovii74.20 (2)Oii—La—Laiv161.84 (3)
Ov—La—Ovii97.88 (2)Oiii—La—Laiv66.64 (3)
Ovi—La—Ovii97.88 (2)Oiv—La—Laiv103.00 (3)
Oi—La—Oviii68.24 (3)Ov—La—Laiv129.62 (3)
Oii—La—Oviii74.20 (2)Ovi—La—Laiv85.04 (3)
Oiii—La—Oviii77.64 (5)Ovii—La—Laiv38.79 (3)
Oiv—La—Oviii148.98 (6)Oviii—La—Laiv103.20 (4)
Ov—La—Oviii97.88 (2)Laix—La—Laiv83.823 (4)
Ovi—La—Oviii97.88 (2)Lax—La—Laiv123.628 (3)
Ovii—La—Oviii136.53 (7)Laxi—La—Laiv123.628 (3)
Oi—La—Laix66.64 (3)Oxii—Mo—Oxiii107.08 (5)
Oii—La—Laix103.00 (3)Oxii—Mo—Oxiv114.36 (10)
Oiii—La—Laix38.85 (3)Oxiii—Mo—Oxiv107.08 (5)
Oiv—La—Laix161.84 (3)Oxii—Mo—O107.08 (5)
Ov—La—Laix85.04 (3)Oxiii—Mo—O114.36 (10)
Ovi—La—Laix129.62 (3)Oxiv—Mo—O107.08 (5)
Ovii—La—Laix103.20 (4)Mo—O—Laiv134.75 (7)
Oviii—La—Laix38.79 (3)Mo—O—Laxv120.66 (7)
Oi—La—Lax103.00 (3)Laiv—O—Laxv102.36 (5)
Oii—La—Lax38.85 (3)
Symmetry codes: (i) y+1/4, x+1/4, z+1/4; (ii) x, y+1/2, z+1; (iii) y1/4, x+1/4, z+1/4; (iv) x, y, z+1; (v) x1/2, y+1/2, z+1/2; (vi) x+1/2, y, z+1/2; (vii) y1/4, x1/4, z+3/4; (viii) y+1/4, x+3/4, z+3/4; (ix) x, y+1, z+1; (x) x+1/2, y+1/2, z+3/2; (xi) x1/2, y+1/2, z+3/2; (xii) y1/4, x+1/4, z+1/4; (xiii) x, y+1/2, z; (xiv) y+1/4, x+1/4, z+1/4; (xv) x+1/2, y1/2, z1/2.

Experimental details

Crystal data
Chemical formulaLa0.667[MoO4]
Crystal system, space groupTetragonal, I41/a
Temperature (K)293
a, c (Å)5.3599 (3), 11.9425 (7)
V3)343.09 (3)
Radiation typeMo Kα
µ (mm1)11.74
Crystal size (mm)0.11 × 0.08 × 0.06
Data collection
DiffractometerNonius KappaCCD
Absorption correctionNumerical
(X-SHAPE; Stoe & Cie, 1995)
Tmin, Tmax0.291, 0.480
No. of measured, independent and
observed [I > 2σ(I)] reflections
2577, 260, 174
(sin θ/λ)max1)0.712
R[F2 > 2σ(F2)], wR(F2), S 0.016, 0.032, 0.98
No. of reflections260
No. of parameters16
Δρmax, Δρmin (e Å3)0.41, 0.37

Computer programs: COLLECT (Nonius, 1998), SCALEPACK (Otwinowski & Minor, 1997), SCALEPACK and DENZO (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006).

Selected bond lengths (Å) top
La—Oi2.5728 (14)Mo—O1.7606 (14)
La—Oii2.5766 (14)
Symmetry codes: (i) y+1/4, x+1/4, z+1/4; (ii) x+1/2, y, z+1/2.
Acknowledgements top

This work was supported by the State of Baden-Württemberg (Stuttgart) and the Deutsche Forschungsgemeinschaft (DFG, Frankfurt/Main) within the funding program Open Access Publishing.