The defect scheelite-type lanthanum(III) ortho-oxidomolybdate(VI) La_0.667[MoO₄]

In scheelite-type La_0.667[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.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Mo-O) = 0.001 Å
• Disorder in main residue
• R factor = 0.016
• wR factor = 0.032
• Data-to-parameter ratio = 16.2

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT774_ALERT_1_B Suspect X-Y Bond in CIF:   LA     --  LA      ..       4.01 Ang.
PLAT774_ALERT_1_B Suspect X-Y Bond in CIF:   LA     --  LA      ..       4.01 Ang.
PLAT774_ALERT_1_B Suspect X-Y Bond in CIF:   LA     --  LA      ..       4.01 Ang.
PLAT774_ALERT_1_B Suspect X-Y Bond in CIF:   LA     --  LA      ..       4.01 Ang.

Alert level C
PLAT041_ALERT_1_C Calc. and Reported SumFormula    Strings  Differ          ?
PLAT068_ALERT_1_C Reported F000 Differs from Calcd (or Missing)...          ?
PLAT077_ALERT_4_C Unitcell contains non-integer number of atoms ..          ?
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......      6.690
PLAT906_ALERT_3_C Large K value in the Analysis of Variance ......      3.420

Alert level G
PLAT004_ALERT_5_G Info: Polymeric Structure Found with Dimension .          3
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF          ?
PLAT045_ALERT_1_G Calculated and Reported Z Differ by ............       0.25 Ratio
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        293 K
PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X)  Mo     --  O       ..        7.0 su
PLAT301_ALERT_3_G Note: Main Residue  Disorder ...................         20 Perc.
PLAT794_ALERT_5_G Note: Tentative Bond Valency for Mo      (VI)          5.94
PLAT811_ALERT_5_G No ADDSYM Analysis: Too Many Excluded Atoms ....          !

   0 ALERT level A = Most likely a serious problem - resolve or explain
   4 ALERT level B = A potentially serious problem, consider carefully
   5 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   9 ALERT level G = General information/check it is not something unexpected

   9 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   4 ALERT type 5 Informative message, check

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S1. Comment

The title compound crystallizes isotypically with the already known defect scheelite-type lanthanide ortho-oxidomolybdates(VI) with general formula Ln_0.667[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

For isotypic Ln_0.667[MoO₄] structures with Ln = Ce, Pr, Nd and Sm, see: Schustereit et al. (2011). For synthetic details, see: Liu et al. (2012).

S2. Experimental

Colourless, irregular-shaped single crystals of scheelite-type La_0.667[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.

S3. Refinement

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

Computing details

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

	Fig. 1. Trigonal dodecahedral oxygen environment of the La^3+ 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].
	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)

Crystal data

La0.667[MoO4]	Dx = 4.890 Mg m^−3
Mr = 252.59	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I41/a	Cell parameters from 1769 reflections
Hall symbol: -I 4ad	θ = 0.4–30.5°
a = 5.3599 (3) Å	µ = 11.74 mm^−1
c = 11.9425 (7) Å	T = 293 K
V = 343.09 (3) Å^3	Irregular, colourless
Z = 4	0.11 × 0.08 × 0.06 mm
F(000) = 448

Data collection

Nonius KappaCCD diffractometer	260 independent reflections
Radiation source: fine-focus sealed tube	174 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.046
ω and ϕ scans	θmax = 30.4°, θmin = 4.2°
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1995)	h = −7→7
Tmin = 0.291, Tmax = 0.480	k = −7→7
2577 measured reflections	l = −16→16

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.016	w = 1/[σ^2(Fo^2) + (0.0079P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.032	(Δ/σ)max < 0.001
S = 0.98	Δρmax = 0.41 e Å^−3
260 reflections	Δρmin = −0.37 e Å^−3
16 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0082 (5)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
La	0.0000	0.2500	0.6250	0.01492 (18)	0.6676 (10)
Mo	0.0000	0.2500	0.1250	0.01706 (15)
O	0.1374 (3)	0.0106 (2)	0.20490 (13)	0.0313 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
La	0.0171 (2)	0.0171 (2)	0.0107 (2)	0.000	0.000	0.000
Mo	0.01534 (18)	0.01534 (18)	0.0205 (2)	0.000	0.000	0.000
O	0.0209 (8)	0.0329 (9)	0.0403 (9)	0.0048 (6)	0.0031 (9)	0.0105 (7)

Geometric parameters (Å, º)

La—O^i	2.5728 (14)	La—La^x	4.0120 (2)
La—O^ii	2.5728 (14)	La—La^xi	4.0120 (2)
La—O^iii	2.5728 (14)	La—La^iv	4.0120 (2)
La—O^iv	2.5728 (14)	Mo—O^xii	1.7605 (14)
La—O^v	2.5766 (14)	Mo—O^xiii	1.7605 (14)
La—O^vi	2.5766 (14)	Mo—O^xiv	1.7605 (14)
La—O^vii	2.5766 (14)	Mo—O	1.7606 (14)
La—O^viii	2.5766 (14)	O—La^iv	2.5728 (14)
La—La^ix	4.0120 (2)	O—La^xv	2.5766 (14)
O^i—La—O^ii	128.57 (4)	O^iii—La—La^x	161.84 (3)
O^i—La—O^iii	75.70 (7)	O^iv—La—La^x	66.64 (3)
O^ii—La—O^iii	128.57 (4)	O^v—La—La^x	103.20 (4)
O^i—La—O^iv	128.57 (4)	O^vi—La—La^x	38.79 (3)
O^ii—La—O^iv	75.70 (7)	O^vii—La—La^x	129.62 (3)
O^iii—La—O^iv	128.57 (4)	O^viii—La—La^x	85.04 (3)
O^i—La—O^v	148.98 (6)	La^ix—La—La^x	123.628 (3)
O^ii—La—O^v	68.24 (3)	O^i—La—La^xi	161.84 (3)
O^iii—La—O^v	74.21 (2)	O^ii—La—La^xi	66.64 (3)
O^iv—La—O^v	77.64 (5)	O^iii—La—La^xi	103.00 (3)
O^i—La—O^vi	74.21 (2)	O^iv—La—La^xi	38.85 (3)
O^ii—La—O^vi	77.64 (5)	O^v—La—La^xi	38.79 (3)
O^iii—La—O^vi	148.98 (6)	O^vi—La—La^xi	103.20 (4)
O^iv—La—O^vi	68.24 (3)	O^vii—La—La^xi	85.04 (3)
O^v—La—O^vi	136.53 (7)	O^viii—La—La^xi	129.62 (3)
O^i—La—O^vii	77.64 (5)	La^ix—La—La^xi	123.628 (3)
O^ii—La—O^vii	148.98 (6)	La^x—La—La^xi	83.823 (4)
O^iii—La—O^vii	68.24 (3)	O^i—La—La^iv	38.85 (3)
O^iv—La—O^vii	74.20 (2)	O^ii—La—La^iv	161.84 (3)
O^v—La—O^vii	97.88 (2)	O^iii—La—La^iv	66.64 (3)
O^vi—La—O^vii	97.88 (2)	O^iv—La—La^iv	103.00 (3)
O^i—La—O^viii	68.24 (3)	O^v—La—La^iv	129.62 (3)
O^ii—La—O^viii	74.20 (2)	O^vi—La—La^iv	85.04 (3)
O^iii—La—O^viii	77.64 (5)	O^vii—La—La^iv	38.79 (3)
O^iv—La—O^viii	148.98 (6)	O^viii—La—La^iv	103.20 (4)
O^v—La—O^viii	97.88 (2)	La^ix—La—La^iv	83.823 (4)
O^vi—La—O^viii	97.88 (2)	La^x—La—La^iv	123.628 (3)
O^vii—La—O^viii	136.53 (7)	La^xi—La—La^iv	123.628 (3)
O^i—La—La^ix	66.64 (3)	O^xii—Mo—O^xiii	107.08 (5)
O^ii—La—La^ix	103.00 (3)	O^xii—Mo—O^xiv	114.36 (10)
O^iii—La—La^ix	38.85 (3)	O^xiii—Mo—O^xiv	107.08 (5)
O^iv—La—La^ix	161.84 (3)	O^xii—Mo—O	107.08 (5)
O^v—La—La^ix	85.04 (3)	O^xiii—Mo—O	114.36 (10)
O^vi—La—La^ix	129.62 (3)	O^xiv—Mo—O	107.08 (5)
O^vii—La—La^ix	103.20 (4)	Mo—O—La^iv	134.75 (7)
O^viii—La—La^ix	38.79 (3)	Mo—O—La^xv	120.66 (7)
O^i—La—La^x	103.00 (3)	La^iv—O—La^xv	102.36 (5)
O^ii—La—La^x	38.85 (3)

Symmetry codes: (i) y+1/4, −x+1/4, z+1/4; (ii) x, y+1/2, −z+1; (iii) −y−1/4, x+1/4, z+1/4; (iv) −x, −y, −z+1; (v) x−1/2, y+1/2, z+1/2; (vi) −x+1/2, −y, z+1/2; (vii) −y−1/4, x−1/4, −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) −x−1/2, −y+1/2, −z+3/2; (xii) y−1/4, −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, y−1/2, z−1/2.