Redetermination of the crystal structure of β-zinc molybdate from single-crystal X-ray diffraction data

The crystal structure of the β-polymorph of ZnMoO₄ was re-determined on the basis of single-crystal X-ray diffraction data. In comparison with previous powder X-ray diffraction studies [Katikaneani & Arunachalam (2005). Eur. J. Inorg. Chem. pp. 3080–3087; Cavalcante et al. (2013). Polyhedron, 54, 13–25], all atoms were refined with anisotropic displacement parameters, leading to a higher precision with respect to bond lengths and angles. β-ZnMoO₄ adopts the wolframite structure type and is composed of distorted ZnO₆ and MoO₆ octa­hedra, both with point group symmetry 2. The distortion of the octa­hedra is reflected by variation of bond lengths and angles from 2.002 (3)–2.274 (4) Å, 80.63 (11)–108.8 (2)° for equatorial and 158.4 (2)– 162.81 (14)° for axial angles (ZnO₆), and of 1.769 (3)–2.171 (3) Å, 73.39 (16)–104.7 (2), 150.8 (2)–164.89 (15)° (MoO₆), respectively. In the crystal structure, the same type of MO₆ octa­hedra share edges to built up zigzag chains extending parallel to [001]. The two types of chains are condensed by common vertices into a framework structure. The crystal structure can alternatively be described as derived from a distorted hexa­gonally closed packed arrangement of the O atoms, with Zn and Mo in half of the octa­hedral voids.

1. Related literature

Most molybdates of divalent cations crystallize either in the scheelite-type or in the wolframite-type (Macavei & Schulz, 1993). Zinc molybdate (ZnMoO₄) is an inorganic semiconductor. It adopts the wolframite-type of structure (Keeling, 1957) and is dimorphic. The two phases, referred to as α- (triclinc symmetry) and β- (monoclinic symmetry), can be selectively obtained by controlling the synthetic conditions (Abrahams et al., 1967; Zhang et al., 2010). Previous crystal structure refinements of β-ZnMoO₄, based on X-ray powder diffraction data, were reported by Cavalcante et al. (2013) and Katikaneani & Arunachalam (2005). For structure refinement of ZnWO₄, isotypic with the title compound, see: Trots et al. (2009).

2. Experimental

2.1. Crystal data

• ZnMoO₄

• M_r = 225.31

• Monoclinic, P 2/c

• a = 4.6980 (3) Å

• b = 5.7380 (4) Å

• c = 4.8960 (4) Å

• β = 90.311 (7)°

• V = 131.98 (2) ų

• Z = 2

• Mo Kα radiation

• μ = 13.62 mm⁻¹

• T = 293 K

• 0.08 × 0.06 × 0.03 mm

2.2. Data collection

• Oxford Diffraction Xcalibur CCD diffractometer

• Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2014) T_min = 0.905, T_max = 1.000

• 1207 measured reflections

• 405 independent reflections

• 358 reflections with I > 2σ(I)

• R_int = 0.036

2.3. Refinement

• R[F² > 2σ(F²)] = 0.028

• wR(F²) = 0.068

• S = 1.10

• 405 reflections

• 29 parameters

• Δρ_max = 1.20 e Å⁻³

• Δρ_min = −1.17 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2014); cell refinement: CrysAlis RED (Oxford Diffraction, 2014); data reduction: CrysAlis RED; program(s) used to solve structure: SIR2011 (Burla et al., 2012); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012), publCIF (Westrip, 2010) and PARST (Nardelli, 1995).

Supporting information

S1. Synthesis and crystallization

Reagents were used as commercial sources with no further purification. An aqueous solution was prepared by a mixture of 0.047 g 2,2'-bi­pyridine, 0.015 g of molybdenum trioxide and 0.043 g of zinc acetate in 10 ml water. The reaction mixture was stirred at room temperature to homogeneity, then transferred into a teflon-lined stainless steel vessel (40 ml) and heated to 453 K for 48 h under autogenous pressure and after-wards cooled slowly to room temperature. The resulting material was obtained as colorless single-crystals without side products. The solid was filtered off, washed thoroughly with distilled water, and finally air-dried at room temperature.

S2. Refinement

The remaining maximum and minimum electron densities were found 0.77 Å and 0.90 Å, respectively, from the O1 atom. O1 is located on the center of a tree-metal triangle, bridging one Mo and two Zn atoms.

Related literature

Most molybdates of divalent cations crystallize either in the scheelite-type or in the wolframite-type (Macavei & Schulz, 1993). Zinc molybdate (ZnMoO₄) is an inorganic semiconductor. It adopts the wolframite-type of structure (Keeling, 1957) and is dimorphic. The two phases, referred to as α- (triclinc symmetry) and β- (monoclinic symmetry), can be selectively obtained by controlling the synthetic conditions (Abrahams et al., 1967; Zhang et al., 2010). Previous crystal structure refinements of β-ZnMoO₄, based on X-ray powder diffraction data, were reported by Cavalcante et al. (2013) and Katikaneani & Arunachalam (2005). For structure refinement of ZnWO₄, isotypic with the title compound, see: Trots et al. (2009).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2014); cell refinement: CrysAlis RED (Oxford Diffraction, 2014); data reduction: CrysAlis RED (Oxford Diffraction, 2014); program(s) used to solve structure: SIR2011 (Burla et al., 2012); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012), publCIF (Westrip, 2010) and PARST (Nardelli, 1995).

Figures

Fig. 1. A view of the crystal structure of β-ZnMoO4. Anisotropic displacement parameters are drawn at the 50% probability level.

β-Zinc molybdate

Crystal data

MoO4Zn	F(000) = 208
Mr = 225.31	Dx = 5.670 Mg m^−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
a = 4.6980 (3) Å	Cell parameters from 570 reflections
b = 5.7380 (4) Å	θ = 3.6–31.1°
c = 4.8960 (4) Å	µ = 13.62 mm^−1
β = 90.311 (7)°	T = 293 K
V = 131.98 (2) Å^3	Prism, colourless
Z = 2	0.08 × 0.06 × 0.03 mm

Data collection

Oxford Diffraction Xcalibur CCD diffractometer	405 independent reflections
Radiation source: Enhance (Mo) X-ray Source	358 reflections with I > 2σ(I)
Detector resolution: 10.2673 pixels mm^-1	Rint = 0.036
ω– and ϕ–scans	θmax = 31.3°, θmin = 3.6°
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2014)	h = −6→6
Tmin = 0.905, Tmax = 1.000	k = −8→8
1207 measured reflections	l = −6→6

Refinement

Refinement on F^2	29 parameters
Least-squares matrix: full	0 restraints
R[F^2 > 2σ(F^2)] = 0.028	w = 1/[σ^2(Fo^2) + (0.0209P)^2 + 0.5403P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.068	(Δ/σ)max < 0.001
S = 1.10	Δρmax = 1.20 e Å^−3
405 reflections	Δρmin = −1.17 e Å^−3

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.

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

	x	y	z	Uiso*/Ueq
Mo1	1.0000	0.81190 (10)	0.2500	0.00507 (18)
Zn1	1.5000	0.69182 (15)	0.7500	0.0092 (2)
O1	1.2538 (7)	0.6236 (6)	0.4014 (7)	0.0080 (7)
O2	0.7835 (7)	0.8950 (6)	0.5603 (7)	0.0058 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.0065 (3)	0.0045 (3)	0.0041 (3)	0.000	−0.0002 (2)	0.000
Zn1	0.0087 (4)	0.0116 (4)	0.0073 (4)	0.000	0.0009 (3)	0.000
O1	0.0089 (17)	0.0110 (16)	0.0041 (17)	0.0006 (14)	0.0003 (13)	−0.0004 (14)
O2	0.0088 (16)	0.0064 (14)	0.0021 (16)	−0.0005 (13)	0.0016 (12)	−0.0010 (13)

Geometric parameters (Å, º)

Mo1—O1^i	1.769 (3)	Zn1—O2^iv	2.002 (3)
Mo1—O1	1.769 (3)	Zn1—O2^v	2.002 (3)
Mo1—O2	1.894 (3)	Zn1—O1^vi	2.094 (3)
Mo1—O2^i	1.894 (3)	Zn1—O1	2.094 (3)
Mo1—O2^ii	2.171 (3)	Zn1—O1^vii	2.274 (4)
Mo1—O2^iii	2.171 (3)	Zn1—O1^viii	2.274 (4)
O1^i—Mo1—O1	104.7 (2)	O2^iv—Zn1—O1	95.54 (14)
O1^i—Mo1—O2	97.25 (15)	O2^v—Zn1—O1	96.96 (14)
O1—Mo1—O2	100.46 (15)	O1^vi—Zn1—O1	158.4 (2)
O1^i—Mo1—O2^i	100.46 (15)	O2^iv—Zn1—O1^vii	162.81 (14)
O1—Mo1—O2^i	97.25 (15)	O2^v—Zn1—O1^vii	88.37 (13)
O2—Mo1—O2^i	150.8 (2)	O1^vi—Zn1—O1^vii	82.25 (14)
O1^i—Mo1—O2^ii	164.89 (14)	O1—Zn1—O1^vii	80.63 (11)
O1—Mo1—O2^ii	88.90 (14)	O2^iv—Zn1—O1^viii	88.37 (13)
O2—Mo1—O2^ii	73.39 (16)	O2^v—Zn1—O1^viii	162.81 (14)
O2^i—Mo1—O2^ii	84.01 (11)	O1^vi—Zn1—O1^viii	80.63 (11)
O1^i—Mo1—O2^iii	88.90 (14)	O1—Zn1—O1^viii	82.24 (14)
O1—Mo1—O2^iii	164.89 (15)	O1^vii—Zn1—O1^viii	74.53 (18)
O2—Mo1—O2^iii	84.01 (11)	Mo1—O1—Zn1	126.54 (19)
O2^i—Mo1—O2^iii	73.39 (16)	Mo1—O1—Zn1^viii	133.83 (18)
O2^ii—Mo1—O2^iii	78.49 (18)	Zn1—O1—Zn1^viii	97.75 (14)
O2^iv—Zn1—O2^v	108.8 (2)	Mo1—O2—Zn1^ix	125.93 (18)
O2^iv—Zn1—O1^vi	96.96 (14)	Mo1—O2—Mo1^ii	106.61 (16)
O2^v—Zn1—O1^vi	95.54 (14)	Zn1^ix—O2—Mo1^ii	124.32 (17)

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