A tetra­gonal form of dysprosium orthomolybdate at room temperature

Dorzhieva, S.; Chumak, I.; Sarapulova, A.; Mikhailova, D.; Bazarova, J.; Ehrenberg, H.

doi:10.1107/S0108270111033713

inorganic compounds

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 67| Part 10| October 2011| Pages i50-i52

doi:10.1107/S0108270111033713

A tetragonal form of dysprosium orthomolybdate at room temperature

Sesegma Dorzhieva,^a Ihor Chumak,^b Angelina Sarapulova,^b ^* Daria Mikhailova,^b Jibzema Bazarova ^a and Helmut Ehrenberg ^c

^aBaikal Institute of Nature Management, Siberian Branch of the Russian Academy of Sciences, Sakhyanova Street 6, Ulan-Ude, Russian Federation, ^bInstitute for Complex Materials, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany, and ^cKarlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
^*Correspondence e-mail: a.e.sarapulova@ifw-dresden.de

(Received 15 June 2011; accepted 18 August 2011; online 15 September 2011)

In the present tetragonal modification of dysprosium orthomolybdate, Dy₂(MoO₄)₃, the Dy, one Mo and one O atom are located on a mirror plane with Wyckoff symbol 4e, while another Mo atom is located on a fourfold inverse axis, Wyckoff symbol 2a. A single crystal was selected from a polycrystalline mixture of the Dy₂O₃–ZrO₂–MoO₃ system and was stable at room temperature for at least three months. The structure refinement does not indicate the presence of Zr on the Dy sites (to within 1% accuracy). Thus, the stabilization of the tetragonal form is due to disordered positions for a second O atom and split positions for a third O atom that also maintain the DyO₇ coordination, which is not expected for short Dy—O distances [2.243 (6)–2.393 (5) Å].

Comment

It is known that the molybdates of the rare earth elements show interesting fluorescence, laser, piezoelectric, ferroelectric and ferroelastic properties, and they are used as catalysts for the oxidation of organic compounds such as toluene and isobutene (Smet et al., 2001 ; Wang et al., 2008 ; Nassau et al., 1971 ; Wenxing et al., 1999 ). The crystal chemistry of molybdenum compounds is very rich because Mo adopts different oxidation states and therefore forms various coordination polyhedra, such as tetrahedra (Nassau et al., 1971), pyramids (Alonso et al., 2004 ) and octahedra (Gall et al., 2002 ). For example, Gall et al. (2002) synthesized molybdates R₄Mo₄O₁₁ (R = Gd–Tm) with an average oxidation state for Mo of +2.5 and explained the stabilization of the crystal structures through the distortion of trans-edge-sharing Mo octahedra, based on theoretical calculations. With higher oxidation states Mo forms fivefold oxygen coordination, as in the Dy₂MoO₆ structure (Alonso et al., 2004).

Rare earth molybdates with M₂(MoO₄)₃ stoichiometry exist in several polymorphs, depending on the temperature and the specific rare earth element (Nassau et al., 1971). A high-temperature β-form is stable at temperatures above 1023–1153 K. The transition from the β-modification to the room-temperature α-form is kinetically prevented during cooling and takes place via a β′ phase, which is metastable at room temperature for a long time. For example, crystals of Gd₂(MoO₄)₃ exist in the metastable Pba2 (Keve et al., 1970 ) form under ambient conditions for years, although the stable low-temperature form is monoclinic (Nassau et al., 1971). Both the tetragonal and orthorhombic polymorphic modifications contain a network of corner-sharing polyhedra, in which Gd and Mo cations are coordinated by seven and four O atoms, respectively.

Borchardt & Bierstedt (1967 ) showed that Gd₂(MoO₄)₃ and the isostructural molybdates of Sm, Eu, Tb and Dy undergo ferroelectric phase transformations in the temperature range 423 K < T₀ < 463 K. Gadolinium molybdate, Gd₂(MoO₄)₃, with a ferroelectric–ferroelastic transition temperature of about 433 K, crystallizes in the space group Pba2 (metastable form) below the phase transition and in the space group P $[\overline{4}]$ 2₁m above it (Jeitschko, 1972 ). The paraelectric structure at elevated temperature approaches the average structure of the two ferroelectric–ferroelastic orientations (Jeitschko, 1972). Zou et al. (1999 ) mentioned that the β-modification of (Nd_0.023Gd_0.977)₂(MoO₄)₃ with tetragonal symmetry can exist at room temperature.

Dysprosium molybdate, Dy₂(MoO₄)₃, shows a ferroelectric–ferroelastic transition below 418 K (Roy et al., 1989 ). According to X-ray powder diffraction, the ferroelectric phase crystallizes in orthorhombic symmetry (space group Pba2; Roy et al., 1989). Above 1303 K, a reconstructive phase transition into a cubic form of Dy₂(MoO₄)₃ was reported (Roy et al., 1989; Brixner, 1973 ).

In this work, single crystals of Dy₂(MoO₄)₃ have been obtained with the high-temperature β-form tetragonal crystal structure, and the structure refinement based on room-temperature single-crystal X-ray diffraction data has been performed.

According to the single-crystal experiment, dysprosium molybdate shows tetragonal symmetry at room temperature, space group P $[\overline{4}]$ 2₁m, with unit-cell parameters a = 7.295 (2) Å and c = 10.578 (4) Å. On the one hand, the reason for the existence of the tetragonal high-temperature structure at room temperature is not clear, because a monoclinic form of Dy₂(MoO₄)₃ has been observed below 1043 K (Nassau et al., 1971). On the other hand, the symmetry of the low-temperature forms of related compounds is strongly dependent on the synthesis conditions and cation stoichiometry. For example, for the Nd-substituted phase (Nd_0.023Gd_0.977)₂(MoO₄)₃, obtained by the Czochralsky method, a tetragonal crystal structure was found at room temperature by Zou et al. (1999). Even a 2% cation substitution of Gd through Nd stabilizes a high-temperature form in the space group P $[\overline{4}]$ 2₁m with a = 7.356 (1) Å and c = 10.685 (2) Å. The tetragonal Dy₂(MoO₄)₃ form, obtained in the present work, is stable at room temperature for at least three months (the structure investigation was repeated after three months in storage). The stabilization of the tetragonal structure could be due to a small replacement of Dy by Zr atoms, analogous to (Nd_0.023Gd_0.977)₂(MoO₄)₃. However, the refinement of the Dy₂(MoO₄)₃ structure does not indicate the presence of Zr on Dy sites to within 1% accuracy.

The field stability regions for the various types of R₂(MoO₄)₃ structures, shown by Nassau et al. (1971), depend on temperature and the radius of the rare earth cation. The present Dy₂(MoO₄)₃ compound is situated between Gd₂(MoO₄)₃, which has the metastable β′-phase at room temperature, and Y₂(MoO₄)₃, which has a tetragonal modification in the extended temperature region down to room temperature. The crystal structure of Dy₂(MoO₄)₃ is formed by corner-sharing MoO₄ tetrahedra and Dy polyhedra coordinated by seven O atoms (Figs. 1 and 2). In this structure, there are two types of Mo tetrahedra, a regular one and a distorted one, with average Mo—O distances of 1.743 (7) and 1.76 (5) Å, respectively. The DyO₇ polyhedron is characterized by Dy—O distances in the range 2.243 (6)–2.393 (5) Å (Table 1), slightly shorter than those for the coordination polyhedron of Gd in the previously published (Nd_0.023Gd_0.977)₂(MoO₄)₃ structure mentioned above [2.258 (12)–2.418 (8) Å]. Such compression of the structure can be explained by the slightly smaller size of the Dy³⁺ cation (0.97 Å) compared with the Gd³⁺ cation (1.0 Å), according to the Shannon ionic radii (Shannon, 1976 ). For another molybdate, Dy₂MoO₆, with the Mo^VI oxidation state, longer Dy—O interatomic distances [2.381 (6), 2.401 (7) and 2.421 (7) Å] lead to an eightfold oxygen coordination of Dy (Alonso et al., 2004).

Nassau et al. (1971) systematized the crystal structures of R₂(MoO₄)₃ according to their rare earth ionic radii and oxygen coordination polyhedra RO_x. For example, eightfold oxygen coordination is characteristic for the A family of R₂(MoO₄)₃ with large rare earth cations such as La, Pr or Pm, and scheelite- or pseudoscheelite-type structures. Due to the shorter Dy—O distances in the tetragonal form of Dy₂(MoO₄)₃, one would expect a sixfold oxygen coordination of Dy and an orthorhombic crystal structure like Er₂(MoO₄)₃, but the slightly disordered oxygen positions do not distort the structure symmetry and maintain the DyO₇ coordination. Disordered atoms O3 and O4 make the structure more flexible, atom O3 lying in the vicinity of a mirror plane and atom O4 on a general position. The distance from atom O3 to its mirror image is 0.44 (3) Å, and this seems advantageous for sevenfold oxygen coordination.

The shortest metal–metal distances in the title structure are Dy1⋯Mo1ⁱⁱ = 3.7343 (15) Å, Dy1⋯Dy1ⁱⁱ = 3.8572 (17) Å and Mo1⋯Mo1ⁱⁱ = 4.243 (3) Å [symmetry code: (ii) −y + 1, x, −z + 1].

Figure 1
The Dy₂(MoO₄)₃ tetragonal unit cell, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 70% probability level.

Figure 2
The structural model of Dy₂(MoO₄)₃, viewed along the b axis. Dark-grey tetrahedra are formed by Mo atoms and light-grey polyhedra by Dy atoms. The positions for atoms O3, O4A and O4B were taken as the average between two close values.

Experimental

Single crystals of Dy₂(MoO₄)₃ were obtained during an investigation of the Dy₂O₃–ZrO₂–MoO₃ phase diagram in an evacuated sealed silica tube from a Dy₂Zr(MoO₄)₅ composition by heating to 1273 K, followed by cooling at a rate of 5 K h⁻¹ to 1073 K, after which the tube was cooled to room temperature by switching off the heating. From the resulting multiphase polycrystalline mixture, colourless single crystals of Dy₂(MoO₄)₃ were selected using an optical microscope.

Crystal data

Dy₂Mo₃O₁₂
M_r = 804.82
Tetragonal, $[P \overline 42_1 m ]$
a = 7.295 (2) Å
c = 10.578 (4) Å
V = 562.9 (3) Å³
Z = 2
Mo Kα radiation
μ = 16.41 mm⁻¹
T = 296 K
0.08 × 0.06 × 0.06 mm

Data collection

Bruker Kappa APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ) T_min = 0.319, T_max = 0.374
2641 measured reflections
723 independent reflections
645 reflections with I > 2σ(I)
R_int = 0.054

Refinement

R[F² > 2σ(F²)] = 0.029
wR(F²) = 0.045
S = 0.97
723 reflections
44 parameters
Δρ_max = 1.04 e Å⁻³
Δρ_min = −0.88 e Å⁻³
Absolute structure: Flack (1983 ), with 287 Friedel pairs
Flack parameter: 0.02 (2)

Table 1
Selected bond lengths and contact distances (Å)

Dy1—O2	2.243 (6)
Dy1—O3	2.304 (9)
Dy1—O4Aⁱ	2.307 (15)
Dy1—O4Bⁱ	2.351 (14)
Dy1—O1ⁱⁱ	2.393 (5)
Mo1—O4B	1.697 (13)
Mo1—O3	1.745 (9)
Mo1—O1	1.784 (8)
Mo1—O4A	1.803 (16)
Mo2—O2	1.743 (7)
Symmetry codes: (i) y, -x+1, -z+1; (ii) -y+1, x, -z+1.

Due to the large atomic displacement parameters, a split position from the original position on a mirror plane was introduced for atom O3, with an occupancy of 0.5. Atom O4 was disordered over two sites (O4A and O4B) separated by 0.63 (2) Å. Atoms O4A and O4B were refined with a common displacement parameter and their occupancy factor was constrained to sum to 1. These positions (O3, O4A and O4B) were then refined with isotropic displacement parameters.

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S0108270111033713/lg3065sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S0108270111033713/lg3065Isup2.hkl

Comment top

It is known that the molybdates of the rare earth elements show interesting fluorescence, laser, piezoelectric, ferroelectric and ferroelastic properties, and are used as catalysts for the oxidation of organic compounds such as toluene or isobutene (Smet et al., 2001; Wang et al., 2008; Nassau et al., 1971; Wenxing et al., 1999). The crystal chemistry of molybdenum compounds is very rich, because Mo adopts different oxidation states and therefore forms various coordination polyhedra, such as tetrahedra (Nassau et al., 1971), pyramids (Alonso et al., 2004) and octahedra (Gall et al., 2002). For example, Gall et al. (2002) synthesized molybdates R₄Mo₄O₁₁ (R = Gd–Tm) with an average oxidation state for Mo of +2.5 and explained the stabilization of the crystal structures through the distortion of trans-edge-sharing Mo octahedra, based on theoretical calculations. With higher oxidation states Mo forms five-fold oxygen coordination, as in the Dy₂MoO₆ structure (Alonso et al., 2004).

Rare earth molybdates with M₂(MoO₄)₃ stoichiometry exist in several polymorphs depending on the temperature and the specific rare earth element (Nassau et al., 1971). A high-temperature β-form is stable at temperatures above 1023–1153 K. The transition from the β-modification to the room-temperature α-form is kinetically prevented during cooling and takes place via a β' phase, which is metastable at room temperature for a long time. For example, crystals of Gd₂(MoO₄)₃ exist in the metastable Pba2 (Keve et al., 1970) form under ambient conditions for years, although the stable low-temperature form is monoclinic (Nassau et al., 1971). Both tetragonal and orthorhombic polymorphic modifications contain a network of corner-sharing polyhedra, in which Gd and Mo cations are coordinated by seven and four O atoms, respectively.

Borchardt & Bierstedt (1967) showed that Gd₂(MoO₄)₃ and the isostructural molybdates of Sm, Eu, Tb and Dy undergo ferroelectric phase transformations in the temperature range 423 K < T₀ < 463 K. Gadolinium molybdate, Gd₂(MoO₄)₃, with a ferroelectric–ferroelastic transition temperature of about 433 K, crystallizes in the space group Pba2 (metastable form) below the phase transition and in the space group P42₁m above it (Jeitschko, 1972). The paraelectric structure at elevated temperature approaches the average structure of the two ferroelectric–ferroelastic orientations (Jeitschko, 1972). Zou et al. (1999) mentioned that the β-modification of (Nd_0.023Gd_0.977)₂(MoO₄)₃ with tetragonal symmetry can exist at room temperature.

Dysprosium molybdate, Dy₂(MoO₄)₃, shows a ferroelectric–ferroelastic transition below 418 K (Roy et al., 1989). According to X-ray powder diffraction, the ferroelectric phase crystallizes in orthorhombic symmetry (space group Pba2; Roy et al., 1989). Above 1303 K, a reconstructive phase transition into a cubic form of Dy₂(MoO₄)₃ was reported (Roy et al., 1989; Brixner, 1973).

In this work, single crystals of Dy₂(MoO₄)₃ with the high-temperature β-form tetragonal crystal structure have been obtained, and the structure refinement based on single-crystal X-ray diffraction data has been performed at room temperature.

According to the single-crystal experiment, dysprosium molybdate shows tetragonal symmetry at room temperature, space group P42₁m, with unit-cell parameters a = 7.295 (2) Å and c = 10.578 (4) Å. On the one hand, the reason for the existence of the tetragonal high-temperature structure at room temperature is not clear, because a monoclinic form of Dy₂(MoO₄)₃ has been observed below 1043 K (Nassau et al., 1971). On the other hand, the symmetry of the low-temperature forms of related compounds is strongly dependent on the synthesis conditions and cation stoichiometry. For example, for the Nd-substituted phase (Nd_0.023Gd_0.977)₂(MoO₄)₃, obtained by the Czochralsky method, a tetragonal crystal structure was found by Zou et al. (1999) at room temperature. Even a 2% cation substitution of Gd through Nd stabilizes a high-temperature form in space group P42₁m with a = 7.356 (1) Å and c = 10.685 (2) Å. The tetragonal Dy₂(MoO₄)₃ form, obtained in present work, is stable at room temperature for at least three months (the structure investigation was repeated after three months in storage). The stabilization of the tetragonal structure could be due to a small replacement of Dy by Zr atoms, analogous to (Nd_0.023Gd_0.977)₂(MoO₄)₃. However, the refinement of the Dy₂(MoO₄)₃ structure does not indicate the presence of Zr on Dy sites to within 1% inaccuracy.

The field stability regions for the various types of R₂(MoO₄)₃ structures, shown by Nassau et al. (1971), depend on temperature and the radius of the rare earth cation. The present Dy₂(MoO₄)₃ compound is situated between Gd₂(MoO₄)₃, which has the metastable β'-phase at room temperature, and Y₂(MoO₄)₃, which has a tetragonal modification in the extended temperature region down to room temperature. The crystal structure of Dy₂(MoO₄)₃ is formed by corner-sharing MoO₄ tetrahedra and Dy polyhedra coordinated by seven O atoms (Figs. 1 and 2). In this structure there are two types of Mo tetrahedra, a regular one and a distorted one, with average Mo—O distances of 1.743 (7) and 1.76 (5) Å, respectively. The DyO₇ polyhedron is characterized by Dy—O distances in the range 2.243 (6)–2.393 (5) Å (Table 1), slightly shorter than those for the coordination polyhedron of Gd in the previously published (Nd_0.023Gd_0.977)₂(MoO₄)₃ structure mentioned above [2.258 (12)–2.418 (8) Å]. Such compression of the structure can be explained by the slightly smaller size of the Dy³⁺ cation (0.97 Å) compared with the Gd³⁺ cation (1.0 Å), according to the Shannon ionic radii (Shannon, 1976). For another molybdate, Dy₂MoO₆, with the Mo^VI oxidation state, longer Dy—O interatomic distances [2.381 (6), 2.401 (7) and 2.421 (7) Å) lead to an eight-fold oxygen coordination of Dy (Alonso et al., 2004).

Nassau et al. (1971) systematized the crystal structures of R₂(MoO₄)₃ according to their rare earth ionic radius and oxygen coordination polyhedra RO_x. For example, eight-fold oxygen coordination is characteristic for the A family of R₂(MoO₄)₃ with large rare earth cations such as La, Pr or Pm, and scheelite- or pseudoscheelite-type structures. Due to the shorter Dy—O distances in the tetragonal form of Dy₂(MoO₄)₃, one would expect a six-fold oxygen coordination of Dy and an orthorhombic crystal structure like Er₂(MoO₄)₃, but the slightly disordered oxygen positions do not distort the structure symmetry and maintain the DyO₇ coordination. Disordered atoms O3 and O4 make the structure more flexible, atom O3 lying in the vicinity of a mirror plane and atom O4 on a general position. The distance from atom O3 to its mirror image is 0.44 (3) Å, and this seems advantageous for seven-fold oxygen coordination.

The shortest metal···metal distances in the title structure are Dy1···Mo1(-y + 1, x, -z + 1) = 3.7343(15 Å, Dy1···Dy1(-y + 1, x, -z + 1) = 3.8572 (17) Å and Mo1···Mo1(-y + 1, x, -z + 1) = 4.243 (3) Å.

Related literature top

For related literature, see: Alonso et al. (2004); Borchardt & Bierstedt (1967); Brixner (1973); Gall et al. (2002); Jeitschko (1972); Keve et al. (1970); Nassau et al. (1971); Roy et al. (1989); Shannon (1976); Smet et al. (2001); Wang et al. (2008); Wenxing et al. (1999); Zou et al. (1999).

Experimental top

Single crystals of Dy₂(MoO₄)₃ were obtained during an investigation of the Dy₂O₃–ZrO₂–MoO₃ phase diagram in an evacuated sealed silica tube from a Dy₂Zr(MoO₄)₅ composition by heating up to 1273 K, followed by cooling at a rate of 5 K h^-1 down to 1073 K, after which the tube was cooled to room temperature by switching off the heating. From the resulting multiphase polycrystalline mixture, colourless single crystals of Dy₂(MoO₄)₃ were selected using an optical microscope.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. The Dy₂(MoO₄)₃ tetragonal unit cell, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 70% probability level.
	Fig. 2. The structural model of Dy₂(MoO₄)₃, viewed along the b axis. Dark-grey tetrahedra are formed by Mo atoms and light-grey polyhedra by Dy atoms. The positions for atoms O3, O4A and O4B were taken as the average between two close values.

Dysprosium orthomolybdate top

Crystal data top

Dy₂Mo₃O₁₂	D_x = 4.748 Mg m⁻³
M_r = 804.82	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P42₁m	Cell parameters from 727 reflections
Hall symbol: P -4 2ab	θ = 1.9–27.5°
a = 7.295 (2) Å	µ = 16.41 mm⁻¹
c = 10.578 (4) Å	T = 296 K
V = 562.9 (3) Å³	Prism, colourless
Z = 2	0.08 × 0.06 × 0.06 mm
F(000) = 708

Data collection top

Bruker Kappa APEXII CCD area-detector diffractometer	723 independent reflections
Radiation source: fine-focus sealed tube	645 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.054
Detector resolution: 25 pixels mm^-1	θ_max = 27.5°, θ_min = 1.9°
ϕ scans	h = −8→9
Absorption correction: multi-scan (SADABS; Bruker, 2004)	k = −9→7
T_min = 0.319, T_max = 0.374	l = −13→8
2641 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0063P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.029	(Δ/σ)_max = 0.001
wR(F²) = 0.045	Δρ_max = 1.04 e Å⁻³
S = 0.97	Δρ_min = −0.88 e Å⁻³
723 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
44 parameters	Extinction coefficient: 0.00073 (19)
0 restraints	Absolute structure: Flack (1983), with 287 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.02 (2)

Crystal data top

Dy₂Mo₃O₁₂	Z = 2
M_r = 804.82	Mo Kα radiation
Tetragonal, P42₁m	µ = 16.41 mm⁻¹
a = 7.295 (2) Å	T = 296 K
c = 10.578 (4) Å	0.08 × 0.06 × 0.06 mm
V = 562.9 (3) Å³

Data collection top

Bruker Kappa APEXII CCD area-detector diffractometer	723 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2004)	645 reflections with I > 2σ(I)
T_min = 0.319, T_max = 0.374	R_int = 0.054
2641 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.029	0 restraints
wR(F²) = 0.045	Δρ_max = 1.04 e Å⁻³
S = 0.97	Δρ_min = −0.88 e Å⁻³
723 reflections	Absolute structure: Flack (1983), with 287 Friedel pairs
44 parameters	Absolute structure parameter: 0.02 (2)

Special details top

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) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Dy1	0.81307 (5)	0.31307 (5)	0.26269 (5)	0.00987 (17)
Mo1	0.79435 (11)	0.29435 (11)	0.64262 (10)	0.0107 (3)
Mo2	1.0000	0.0000	0.0000	0.0127 (4)
O1	0.6285 (8)	0.1285 (8)	0.6903 (9)	0.014 (2)
O2	0.9586 (8)	0.1890 (9)	0.0967 (6)	0.0226 (15)
O3	0.8279 (18)	0.2853 (18)	0.4794 (8)	0.014 (3)*	0.50
O4A	0.683 (3)	0.505 (2)	0.6869 (16)	0.020 (2)*	0.48 (2)
O4B	0.762 (3)	0.5017 (18)	0.7117 (14)	0.020 (2)*	0.52 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Dy1	0.0104 (2)	0.0104 (2)	0.0087 (3)	−0.0025 (3)	−0.00039 (19)	−0.00039 (19)
Mo1	0.0109 (3)	0.0109 (3)	0.0102 (6)	−0.0027 (5)	−0.0001 (3)	−0.0001 (3)
Mo2	0.0165 (5)	0.0165 (5)	0.0052 (7)	0.000	0.000	0.000
O1	0.010 (3)	0.010 (3)	0.022 (5)	0.001 (3)	0.001 (3)	0.001 (3)
O2	0.026 (4)	0.027 (4)	0.015 (3)	−0.002 (4)	0.006 (3)	−0.008 (4)

Geometric parameters (Å, º) top

Dy1—O2ⁱ	2.243 (6)	Mo1—O1	1.784 (8)
Dy1—O2	2.243 (6)	Mo1—O4A	1.803 (16)
Dy1—O3ⁱ	2.304 (9)	Mo1—O4Aⁱ	1.803 (16)
Dy1—O3	2.304 (9)	Mo2—O2^vi	1.743 (7)
Dy1—O4Aⁱⁱ	2.307 (15)	Mo2—O2	1.743 (7)
Dy1—O4Aⁱⁱⁱ	2.307 (15)	Mo2—O2^vii	1.743 (7)
Dy1—O4Bⁱⁱ	2.351 (14)	Mo2—O2^viii	1.743 (7)
Dy1—O4Bⁱⁱⁱ	2.351 (14)	O1—Dy1ⁱⁱ	2.393 (5)
Dy1—O1^iv	2.393 (5)	O1—Dy1^ix	2.393 (5)
Dy1—O1^v	2.393 (5)	O3—O3ⁱ	0.44 (3)
Mo1—O4Bⁱ	1.697 (13)	O4A—O4B	0.632 (17)
Mo1—O4B	1.697 (13)	O4A—Dy1^iv	2.307 (15)
Mo1—O3	1.745 (9)	O4B—Dy1^iv	2.351 (14)
Mo1—O3ⁱ	1.745 (9)

O2ⁱ—Dy1—O2	76.6 (3)	O4Bⁱⁱⁱ—Dy1—O4A^x	62.2 (7)
O2ⁱ—Dy1—O3ⁱ	136.2 (4)	O1^iv—Dy1—O4A^x	117.2 (3)
O2—Dy1—O3ⁱ	147.1 (4)	O1^v—Dy1—O4A^x	50.5 (3)
O2ⁱ—Dy1—O3	147.1 (4)	O4A^iv—Dy1—O4A^x	161.0 (5)
O2—Dy1—O3	136.2 (4)	O4Bⁱ—Mo1—O4B	93.7 (13)
O3ⁱ—Dy1—O3	11.0 (8)	O4Bⁱ—Mo1—O3	107.2 (7)
O2ⁱ—Dy1—O4Aⁱⁱ	77.4 (4)	O4B—Mo1—O3	118.7 (7)
O2—Dy1—O4Aⁱⁱ	130.3 (5)	O4Bⁱ—Mo1—O3ⁱ	118.7 (7)
O3ⁱ—Dy1—O4Aⁱⁱ	71.6 (5)	O4B—Mo1—O3ⁱ	107.2 (7)
O3—Dy1—O4Aⁱⁱ	79.4 (5)	O3—Mo1—O3ⁱ	14.5 (11)
O2ⁱ—Dy1—O4Aⁱⁱⁱ	130.3 (5)	O4Bⁱ—Mo1—O1	112.8 (6)
O2—Dy1—O4Aⁱⁱⁱ	77.4 (4)	O4B—Mo1—O1	112.8 (6)
O3ⁱ—Dy1—O4Aⁱⁱⁱ	79.4 (5)	O3—Mo1—O1	110.4 (4)
O3—Dy1—O4Aⁱⁱⁱ	71.6 (5)	O3ⁱ—Mo1—O1	110.4 (4)
O4Aⁱⁱ—Dy1—O4Aⁱⁱⁱ	88.3 (10)	O4Bⁱ—Mo1—O4A	114.2 (13)
O2ⁱ—Dy1—O4Bⁱⁱ	79.1 (4)	O4B—Mo1—O4A	20.5 (6)
O2—Dy1—O4Bⁱⁱ	117.0 (5)	O3—Mo1—O4A	110.7 (7)
O3ⁱ—Dy1—O4Bⁱⁱ	79.1 (5)	O3ⁱ—Mo1—O4A	96.9 (8)
O3—Dy1—O4Bⁱⁱ	84.9 (4)	O1—Mo1—O4A	101.5 (6)
O4Aⁱⁱ—Dy1—O4Bⁱⁱ	15.6 (4)	O4Bⁱ—Mo1—O4Aⁱ	20.5 (6)
O4Aⁱⁱⁱ—Dy1—O4Bⁱⁱ	76.1 (8)	O4B—Mo1—O4Aⁱ	114.2 (13)
O2ⁱ—Dy1—O4Bⁱⁱⁱ	117.0 (5)	O3—Mo1—O4Aⁱ	96.9 (8)
O2—Dy1—O4Bⁱⁱⁱ	79.1 (4)	O3ⁱ—Mo1—O4Aⁱ	110.7 (7)
O3ⁱ—Dy1—O4Bⁱⁱⁱ	84.9 (4)	O1—Mo1—O4Aⁱ	101.5 (6)
O3—Dy1—O4Bⁱⁱⁱ	79.1 (5)	O4A—Mo1—O4Aⁱ	134.6 (14)
O4Aⁱⁱ—Dy1—O4Bⁱⁱⁱ	76.1 (8)	O4Bⁱ—Mo1—O4B^xi	71.0 (8)
O4Aⁱⁱⁱ—Dy1—O4Bⁱⁱⁱ	15.6 (4)	O4B—Mo1—O4B^xi	34.6 (6)
O4Bⁱⁱ—Dy1—O4Bⁱⁱⁱ	62.5 (9)	O3—Mo1—O4B^xi	100.1 (4)
O2ⁱ—Dy1—O1^iv	77.2 (3)	O3ⁱ—Mo1—O4B^xi	95.1 (4)
O2—Dy1—O1^iv	117.8 (3)	O1—Mo1—O4B^xi	145.5 (3)
O3ⁱ—Dy1—O1^iv	76.3 (3)	O4A—Mo1—O4B^xi	51.1 (6)
O3—Dy1—O1^iv	82.5 (4)	O4Aⁱ—Mo1—O4B^xi	90.0 (9)
O4Aⁱⁱ—Dy1—O1^iv	96.5 (6)	O4Bⁱ—Mo1—O4B^xii	34.6 (6)
O4Aⁱⁱⁱ—Dy1—O1^iv	152.3 (5)	O4B—Mo1—O4B^xii	71.0 (8)
O4Bⁱⁱ—Dy1—O1^iv	111.8 (5)	O3—Mo1—O4B^xii	95.1 (4)
O4Bⁱⁱⁱ—Dy1—O1^iv	161.1 (4)	O3ⁱ—Mo1—O4B^xii	100.1 (4)
O2ⁱ—Dy1—O1^v	117.8 (3)	O1—Mo1—O4B^xii	145.5 (3)
O2—Dy1—O1^v	77.2 (3)	O4A—Mo1—O4B^xii	90.0 (9)
O3ⁱ—Dy1—O1^v	82.5 (4)	O4Aⁱ—Mo1—O4B^xii	51.1 (6)
O3—Dy1—O1^v	76.3 (3)	O4B^xi—Mo1—O4B^xii	39.8 (5)
O4Aⁱⁱ—Dy1—O1^v	152.3 (5)	O2^vi—Mo2—O2	110.1 (2)
O4Aⁱⁱⁱ—Dy1—O1^v	96.5 (6)	O2^vi—Mo2—O2^vii	110.1 (2)
O4Bⁱⁱ—Dy1—O1^v	161.1 (4)	O2—Mo2—O2^vii	108.1 (4)
O4Bⁱⁱⁱ—Dy1—O1^v	111.8 (5)	O2^vi—Mo2—O2^viii	108.2 (4)
O1^iv—Dy1—O1^v	67.3 (3)	O2—Mo2—O2^viii	110.1 (2)
O2ⁱ—Dy1—O4A^iv	60.1 (3)	O2^vii—Mo2—O2^viii	110.1 (2)
O2—Dy1—O4A^iv	136.4 (3)	O3ⁱ—O3—Mo1	82.8 (5)
O3ⁱ—Dy1—O4A^iv	76.1 (5)	O3ⁱ—O3—Dy1	84.5 (4)
O3—Dy1—O4A^iv	87.1 (5)	Mo1—O3—Dy1	167.0 (9)
O4Aⁱⁱ—Dy1—O4A^iv	47.8 (8)	O4B—O4A—Mo1	70 (2)
O4Aⁱⁱⁱ—Dy1—O4A^iv	134.7 (4)	O4B—O4A—Dy1^iv	86 (2)
O4Bⁱⁱ—Dy1—O4A^iv	62.2 (7)	Mo1—O4A—Dy1^iv	152.3 (11)
O4Bⁱⁱⁱ—Dy1—O4A^iv	123.9 (4)	O4B—O4A—Dy1ⁱⁱ	126 (2)
O1^iv—Dy1—O4A^iv	50.5 (3)	Mo1—O4A—Dy1ⁱⁱ	79.9 (5)
O1^v—Dy1—O4A^iv	117.2 (3)	Dy1^iv—O4A—Dy1ⁱⁱ	127.1 (7)
O2ⁱ—Dy1—O4A^x	136.4 (3)	O4A—O4B—Mo1	89 (2)
O2—Dy1—O4A^x	60.0 (3)	O4A—O4B—Dy1^iv	78 (2)
O3ⁱ—Dy1—O4A^x	87.1 (5)	Mo1—O4B—Dy1^iv	160.6 (9)
O3—Dy1—O4A^x	76.1 (5)	O4A—O4B—Mo1^xii	135 (2)
O4Aⁱⁱ—Dy1—O4A^x	134.7 (4)	Mo1—O4B—Mo1^xii	98.8 (7)
O4Aⁱⁱⁱ—Dy1—O4A^x	47.8 (8)	Dy1^iv—O4B—Mo1^xii	80.5 (4)
O4Bⁱⁱ—Dy1—O4A^x	123.9 (4)

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

Experimental details

Crystal data
Chemical formula	Dy₂Mo₃O₁₂
M_r	804.82
Crystal system, space group	Tetragonal, P42₁m
Temperature (K)	296
a, c (Å)	7.295 (2), 10.578 (4)
V (Å³)	562.9 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	16.41
Crystal size (mm)	0.08 × 0.06 × 0.06

Data collection
Diffractometer	Bruker Kappa APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2004)
T_min, T_max	0.319, 0.374
No. of measured, independent and observed [I > 2σ(I)] reflections	2641, 723, 645
R_int	0.054
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.045, 0.97
No. of reflections	723
No. of parameters	44
Δρ_max, Δρ_min (e Å⁻³)	1.04, −0.88
Absolute structure	Flack (1983), with 287 Friedel pairs
Absolute structure parameter	0.02 (2)

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2008).

Selected bond lengths (Å) top

Dy1—O2ⁱ	2.243 (6)	Mo1—O4B	1.697 (13)
Dy1—O2	2.243 (6)	Mo1—O3	1.745 (9)
Dy1—O3ⁱ	2.304 (9)	Mo1—O3ⁱ	1.745 (9)
Dy1—O3	2.304 (9)	Mo1—O1	1.784 (8)
Dy1—O4Aⁱⁱ	2.307 (15)	Mo1—O4A	1.803 (16)
Dy1—O4Aⁱⁱⁱ	2.307 (15)	Mo1—O4Aⁱ	1.803 (16)
Dy1—O4Bⁱⁱ	2.351 (14)	Mo2—O2^vi	1.743 (7)
Dy1—O4Bⁱⁱⁱ	2.351 (14)	Mo2—O2	1.743 (7)
Dy1—O1^iv	2.393 (5)	Mo2—O2^vii	1.743 (7)
Dy1—O1^v	2.393 (5)	Mo2—O2^viii	1.743 (7)
Mo1—O4Bⁱ	1.697 (13)

Acknowledgements

This work was supported by the Deutscher Akademischer Austauschdienst (DAAD) (postdoctoral fellowship grant to SD).

References

Alonso, J. A., Rivillas, F., Martínez-Lope, M. J. & Pomjakushin, V. (2004). J. Solid State Chem. 177, 2470–2476. Web of Science CrossRef CAS Google Scholar
Borchardt, H. J. & Bierstedt, P. E. (1967). J. Appl. Phys. 38, 2057–2061. CrossRef CAS Web of Science Google Scholar
Brandenburg, K. (2008). DIAMOND. Crystal Impact GbR, Bonn, Germany. Google Scholar
Brixner, L. H. (1973). J. Cryst. Growth, 18, 297–302. CrossRef CAS Web of Science Google Scholar
Bruker (2004). APEX2 (Version 1.08), SAINT (Version 7.03) and SADABS (Version 2.11). Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Gall, P., Barrier, N., Gautier, R. & Gougeon, R. (2002). Inorg. Chem. 41, 2879–2885. Web of Science CrossRef PubMed CAS Google Scholar
Jeitschko, W. (1972). Acta Cryst. B28, 60–76. CrossRef CAS IUCr Journals Web of Science Google Scholar
Keve, E. T., Abrahams, S. C., Nassau, K. & Glass, A. M. (1970). Solid State Commun. 8, 1517–1520. CrossRef CAS Web of Science Google Scholar
Nassau, K., Shiever, J. W. & Keve, E. T. (1971). J. Solid State Chem. 3, 411–419. CrossRef CAS Web of Science Google Scholar
Roy, M., Choudhary, R. N. P. & Acharya, H. N. (1989). J. Therm. Anal. 35, 1471–1476. CrossRef CAS Google Scholar
Shannon, R. D. (1976). Acta Cryst. A32, 751–767. CrossRef CAS IUCr Journals Web of Science Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Smet, F. D., Ruiz, P., Delmon, B. & Devillers, M. (2001). J. Phys. Chem. 105, 12355–12363. Google Scholar
Wang, X., Xian, Y., Wang, G., Shi, J., Su, Q. & Gong, M. (2008). Opt. Mater. 133, 33–39. Google Scholar
Wenxing, K., Yining, F., Kaidong, C. & Yi, C. (1999). J. Catal. 186, 310–317. Google Scholar
Zou, Y.-Q., Chen, L., Gao, X.-Y., Tang, D.-Y. & Luo, Z.-D. (1999). Chin. J. Struct. Chem. 18, 447–450. CAS Google Scholar

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