Crystal structure of defect scheelite-type Nd2/3[WO4]

Knies, B.; Hartenbach, I.

doi:10.1107/S2414314624001755

inorganic compounds

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ISSN: 2414-3146

Volume 9| Part 3| March 2024| x240175

https://doi.org/10.1107/S2414314624001755

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Crystal structure of defect scheelite-type Nd_2/3[WO₄]

Benjamin Knies ^a and Ingo Hartenbach ^a ^*

^aUniversity of Stuttgart, Institute of Inorganic Chemistry, Pfaffenwaldring 55, 70569 Stuttgart, Germany
^*Correspondence e-mail: ingo.hartenbach@iac.uni-stuttgart.de

Edited by M. Weil, Vienna University of Technology, Austria (Received 22 January 2024; accepted 22 February 2024; online 6 March 2024)

Neodymium(III) ortho-oxidotungstate(VI) was synthesized as a side-product in an unsuccessful synthesis attempt at fluoride derivatives of neodymium tungstate in fused silica ampoules, using neodymium(III) oxide, neodymium(III) fluoride and tungsten trioxide. Violet, platelet-shaped single crystals of the title compound emerged of the bulk, which crystallize in the defect scheelite type with a trigonal dodecahedral coordination of oxide anions around the Nd³⁺ cations and the hexavalent tungsten cations situated in the centers of oxide tetrahedra.

Keywords: crystal structure; oxidotungstate(VI); neodymium; scheelite.

CCDC reference: 2312842

Structure description

Nd_2/3[WO₄] crystallizes in the defect scheelite structure type (space group I4₁/a, Dickinson, 1920 ; see Fig. 1). The tungsten cations (Wyckoff position 4a, site symmetry $[\overline{4}]$ ) form regular tetrahedra [WO₄]²⁻ together with four oxide anions, exhibiting a bond length of 1.783 (4) Å. The neodymium cations (Wyckoff position 4b, site symmetry $[\overline{4}]$ ) are coordinated by eight oxide anions, forming a slightly distorted trigonal dodecahedron, in which two different bond lengths, 2.483 (4) Å and 2.516 (4) Å, each one appearing four times, are found (Fig. 2). The distance between two neodymium cations is 3.9116 (2) Å. The corresponding oxidomolybdate(IV), Nd_2/3[MoO₄], crystallizes in the same structure type (Schustereit et al., 2011 ).

Figure 1
Augmented unit cell of Nd_2/3[WO₄] in a view along [100], with [WO₄]²⁻ anions in polyhedral representation and displacement ellipsoids drawn at the 95% probability level.

Figure 2
Cationic coordination sphere around the Nd³⁺ cation in the shape of a trigonal [NdO₈]¹³⁻ dodecahedron; displacement ellipsoids are drawn at the 95% probability level. [Symmetry codes: (i) y − $[{1\over 4}]$ , −x + $[{3\over 4}]$ , z + $[{3\over 4}]$ ; (ii) x − $[{1\over 2}]$ , y, −z + $[{1\over 2}]$ ; (iii) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (iv) −y + $[{1\over 4}]$ , x − $[{1\over 4}]$ , z + $[{3\over 4}]$ ; (v) x − $[{1\over 2}]$ , y − $[{1\over 2}]$ , z + $[{1\over 2}]$ ; (vi) −x + $[{1\over 2}]$ , −y + 1, z + $[{1\over 2}]$ ; (vii) −y + $[{3\over 4}]$ , x − $[{1\over 4}]$ , −z + $[{3\over 4}]$ ; (viii) y − $[{3\over 4}]$ , −x + $[{3\over 4}]$ , −z + $[{3\over 4}]$ ].

Another, formula-analogous polymorph of neodymium(III) ortho-oxidotungstate(VI) with the composition Nd₂[WO₄]₃ is already known in literature (Weil et al., 2009 ), with this compound crystallizing in the scheelite-derived Eu₂[WO₄]₃ structure type (space group C2/c; Templeton & Zalkin, 1963 ). The main difference between these polymorphs is the emergence of a fifth, slightly longer distance from W⁶⁺ to O²⁻ in Nd₂[WO₄]₃, resulting in [W₂O₈]^4– entities, built of two edge-sharing rectangular pyramids being present in its crystal structure, while in the title compound Nd_2/3[WO₄] the [WO₄]²⁻ tetrahedra remain isolated from each other. A rare-earth metal oxidotungstate(VI), crystallizing in the scheelite-type with a fully occupied cationic position is known with Eu²⁺ cations, namely Eu[WO₄] (López-Moreno et al., 2011 ).

Synthesis and crystallization

Single-crystals of Nd_2/3[WO₄] formed in an unsuccessful synthesis attempt to achieve fluoride derivatives of neodymium tungstate, which was performed in fused silica ampoules, utilizing neodymium trifluoride, neodymium(III) oxide and tungsten trioxide as starting materials at approximately 1123 K. The crystals emerged as violet platelets and remained stable under atmospheric conditions.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The site occupancy of the neodymium cations was fixed at 2/3 to maintain electroneutrality.

Table 1
Experimental details

Crystal data
Chemical formula	Nd_2/3[WO₄]
M_r	344.01
Crystal system, space group	Tetragonal, I4₁/a
Temperature (K)	293
a, c (Å)	5.3048 (3), 11.4999 (9)
V (Å³)	323.62 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	45.98
Crystal size (mm)	0.09 × 0.08 × 0.06

Data collection
Diffractometer	Stoe IPDS
Absorption correction	Numerical [X-SHAPE (Stoe & Cie, 1997 ); HABITUS (Herrendorf, 1995 )]
T_min, T_max	0.015, 0.060
No. of measured, independent and observed [I > 2σ(I)] reflections	2201, 291, 231
R_int	0.061
(sin θ/λ)_max (Å⁻¹)	0.754

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.050, 1.01
No. of reflections	291
No. of parameters	15
Δρ_max, Δρ_min (e Å⁻³)	1.08, −1.26
Computer programs: DIF4 and REDU4 (Stoe & Cie, 1991 ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), DIAMOND (Brandenburg & Putz, 2005 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2312842

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314624001755/wm4207sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314624001755/wm4207Isup2.hkl

checkCIF report

Computing details top

Neodymium(III) ortho-oxidotungstate(VI) top

Crystal data top

Nd_0.67[WO₄]	D_x = 7.061 Mg m⁻³
M_r = 344.01	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4₁/a	Cell parameters from 1393 reflections
a = 5.3048 (3) Å	θ = 2.9–33.0°
c = 11.4999 (9) Å	µ = 45.98 mm⁻¹
V = 323.62 (4) Å³	T = 293 K
Z = 4	Platelet, violet
F(000) = 584	0.09 × 0.08 × 0.06 mm

Data collection top

Stoe IPDS diffractometer	291 independent reflections
Radiation source: fine-focus sealed tube	231 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.061
ω–scans	θ_max = 32.4°, θ_min = 4.2°
Absorption correction: numerical [X-SHAPE (Stoe & Cie, 1997); HABITUS (Herrendorf, 1995)]	h = −8→7
T_min = 0.015, T_max = 0.060	k = −8→7
2201 measured reflections	l = −17→17

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0265P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.022	(Δ/σ)_max < 0.001
wR(F²) = 0.050	Δρ_max = 1.08 e Å⁻³
S = 1.01	Δρ_min = −1.26 e Å⁻³
291 reflections	Extinction correction: SHELXL (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
15 parameters	Extinction coefficient: 0.088 (4)

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.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Nd	0.000000	0.250000	0.625000	0.0163 (2)	0.6667
W	0.000000	0.250000	0.125000	0.0135 (2)
O	0.2382 (8)	0.3998 (7)	0.0401 (3)	0.0221 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Nd	0.0176 (3)	0.0176 (3)	0.0139 (4)	0.000	0.000	0.000
W	0.0138 (2)	0.0138 (2)	0.0130 (3)	0.000	0.000	0.000
O	0.026 (2)	0.022 (2)	0.0185 (17)	0.0001 (15)	0.0047 (16)	0.0011 (16)

Geometric parameters (Å, º) top

Nd—Oⁱ	2.483 (4)	Nd—Nd^ix	3.9116 (2)
Nd—Oⁱⁱ	2.483 (4)	Nd—Nd^x	3.9116 (2)
Nd—Oⁱⁱⁱ	2.483 (4)	Nd—Nd^xi	3.9116 (2)
Nd—O^iv	2.483 (4)	Nd—Nd^xii	3.9116 (2)
Nd—O^v	2.516 (4)	W—O^xiii	1.783 (4)
Nd—O^vi	2.516 (4)	W—O^xiv	1.783 (4)
Nd—O^vii	2.516 (4)	W—O^xv	1.783 (4)
Nd—O^viii	2.516 (4)	W—O	1.783 (4)

Oⁱ—Nd—Oⁱⁱ	125.78 (12)	O^v—Nd—O^vii	98.65 (6)
Oⁱ—Nd—Oⁱⁱⁱ	125.78 (12)	O^vi—Nd—O^vii	98.65 (7)
Oⁱⁱ—Nd—Oⁱⁱⁱ	80.25 (19)	Oⁱ—Nd—O^viii	68.34 (10)
Oⁱ—Nd—O^iv	80.2 (2)	Oⁱⁱ—Nd—O^viii	72.96 (8)
Oⁱⁱ—Nd—O^iv	125.78 (12)	Oⁱⁱⁱ—Nd—O^viii	152.39 (16)
Oⁱⁱⁱ—Nd—O^iv	125.78 (12)	O^iv—Nd—O^viii	77.05 (15)
Oⁱ—Nd—O^v	152.39 (16)	O^v—Nd—O^viii	98.65 (7)
Oⁱⁱ—Nd—O^v	68.34 (10)	O^vi—Nd—O^viii	98.65 (6)
Oⁱⁱⁱ—Nd—O^v	77.05 (15)	O^vii—Nd—O^viii	134.35 (18)
O^iv—Nd—O^v	72.96 (8)	O^xiii—W—O^xiv	107.43 (13)
Oⁱ—Nd—O^vi	72.96 (8)	O^xiii—W—O^xv	107.43 (13)
Oⁱⁱ—Nd—O^vi	77.05 (15)	O^xiv—W—O^xv	113.6 (3)
Oⁱⁱⁱ—Nd—O^vi	68.34 (10)	O^xiii—W—O	113.6 (3)
O^iv—Nd—O^vi	152.39 (16)	O^xiv—W—O	107.43 (13)
O^v—Nd—O^vi	134.35 (18)	O^xv—W—O	107.43 (13)
Oⁱ—Nd—O^vii	77.05 (15)	W—O—Ndⁱⁱⁱ	132.2 (2)
Oⁱⁱ—Nd—O^vii	152.39 (16)	W—O—Nd^xvi	120.51 (19)
Oⁱⁱⁱ—Nd—O^vii	72.96 (8)	Ndⁱⁱⁱ—O—Nd^xvi	102.95 (15)
O^iv—Nd—O^vii	68.34 (10)

Symmetry codes: (i) y−1/4, −x+3/4, z+3/4; (ii) x−1/2, y, −z+1/2; (iii) −x+1/2, −y+1/2, −z+1/2; (iv) −y+1/4, x−1/4, z+3/4; (v) x−1/2, y−1/2, z+1/2; (vi) −x+1/2, −y+1, z+1/2; (vii) −y+3/4, x−1/4, −z+3/4; (viii) y−3/4, −x+3/4, −z+3/4; (ix) −x, −y, −z+1; (x) −x+1/2, −y+1/2, −z+3/2; (xi) −x−1/2, −y+1/2, −z+3/2; (xii) −x, −y+1, −z+1; (xiii) −x, −y+1/2, z; (xiv) −y+1/4, x+1/4, −z+1/4; (xv) y−1/4, −x+1/4, −z+1/4; (xvi) x+1/2, y+1/2, z−1/2.

Funding information

Funding for this research was provided by: a German Research Foundation (DFG) grant ‘Open Access Publication Funding/2023–2024/University of Stuttgart’ (512689491).

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