Download citation
Download citation
link to html
Crystals of mercury(II) tungstate(VI), HgWO4, were grown in sealed gold tubes under an Ar atmosphere at 300 MPa and 973 K. The monoclinic crystal structure (C2/c) of HgWO4 consists of zigzag chains of edge-sharing WO6 octahedra running along the c axis and layers of very distorted corner-sharing HgO6 octahedra in the bc plane. The Hg atom lies on an inversion centre and the W atom is on a twofold axis. No structural effects which can be ascribed to the high pressure used in the synthesis were found.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102000379/iz1018sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102000379/iz1018Isup2.hkl
Contains datablock I

Comment top

Tungstates are of interest for their luminescent properties, for use as detectors and calorimeters in high-energy experiments and in X-ray imaging. Strong absorption of high-energy radiation, in combination with a high density (9.2 Mg m-3), are some of the attractive properties of the title compound.

The crystal structure of HgWO4 has recently been determined from powder data by Rietveld refinements of neutron diffraction data (Åsberg Dahlborg et al., 2000). The two main differences between the previous powder study and the present single-crystal study are, firstly, isotropic displacement parameters were used in the powder study and secondly, the high pressure used here for the growth of single crystals. In order to correlate structure with luminescent properties, precise structural information is needed, preferably from single-crystal data. This prompted us to perform the study which is presented in this paper.

HgWO4 has a structure related to that of wolframite (Keeling, 1957) and is isostructural with HgMoO4 (Jeitschko & Sleight, 1973). The structure consists of zigzag chains of edge-sharing WO6 octahedra extending parallel to the c axis. There are two short W—O bonds [1.733 (5) Å], two medium [1.953 (4) Å] and two long bonds [2.197 (5) Å]. The O1—O1(-x, -y, -z) edge distance shared between connected WO6 octahedra is only 2.372 (8) Å, while the others are in the range 2.753 (8)–2.916 (8) Å. The W atom is displaced 0.337 Å from the centre of the WO6 octahedron, calculated as the centre of gravity.

In the bc plane, layers of corner-sharing HgO6 octahedra are formed. The HgO6 octahedra are very distorted, with two short collinear Hg—O bonds [2.044 (4) Å] and two pairs of long Hg—O distances [2.633 (5) and 2.743 (5) Å, respectively]. If the next O atoms, at a distance of 3.131 (5) Å from Hg, are included in the coordination, Hg is eight-coordinate. These HgO8 polyhedra can be described as a distorted cubes. The layer in the bc plane is then formed by edge-sharing HgO8-cubes.

The only significant difference in bond distances in this study, compared with the neutron powder diffraction study, is the shorter W—W distance of 3.4143 (4) Å, compared with 3.425 (4) Å in the powder study. All the W—O distances are slightly shorter, and all the Hg—O distances are slightly longer, in the present single-crystal structure determination.

Displacement ellipsoids show that Hg has the largest displacements in the plane of the four long Hg—O bonds of the HgO6 octahedron, as expected. Ueq is smaller for O1 than for Hg, which is in agreement with the neutron powder refinement. The displacement parameters for W are small and only slightly anisotropic.

Despite the differences in pressure, sample preparation and experimental data collection, there are very small differences between the results from the present single-crystal determination and the older structure determined from powder data. No effects which can be ascribed to the high pressure used for single-crystal synthesis have been found.

Experimental top

Colourless prismatic crystals of HgWO4 were synthesized under high gas pressure in collapsible gold tubes. The reaction mixture was composed of Na2WO4·2H2O (Johnson Matthey, 95%) and HgCl2 (Merck, 99.5%) in a 1:1 ratio. The reactants were loaded into a gold tube, which was then welded shut and put inside a three-zone kanthal furnace, which is part of a high-pressure system (Lada et al., 1998). The pressure was increased to 300 MPa using Ar as the pressure medium and the temperature was adjusted to 973 K. After 10 h, the temperature was brought down to room temperature within a few hours, then the pressure was decreased to 1 atm (1 atm = 101325 Pa). The resulting prismatic crystals of HgWO4 were washed with water. The largest crystals were about 1 mm in the longest direction.

Refinement top

The maximum extinction correction (SHELXL97; Sheldrick, 1997) was y = 0.84 for the 111 reflection (the observed structure factor is Fobs = yFkin, where Fkin is the kinematic value of the structure factor). The highest residual electron density peak was located 0.95 Å from O2 and 0.97 Å from W. There were also peaks between Hg and O1.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: LATCON (Schwarzenbach & King, 1999); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. A polyhedral representation of HgWO4 viewed along the c axis, with b horizontal. The WO6 octahedra are dark grey and the HgO6 octahedra are light grey.
[Figure 2] Fig. 2. An ORTEP-3 plot (Farrugia, 1997) of the Hg and W coordination to O atoms in HgWO4. Displacement ellipsoids are drawn at the 80% probability level [symmetry codes: (i) -x, -y, -z; (ii) -x, y, 1/2 - z; (iii) x, -y, 1/2 + z; (iv) x, y, 1 + z; (v) 1/2 - x, 1/2 - y, 1 - z; (vi) 1/2 - x, 1/2 + y, 3/2 - z; (vii) x, 1 - y, 1/2 + z; (viii) 1/2 - x, 1/2 - y, 2 - z; (ix) 1/2 - x, y - 1/2, 3/2 - z].
mercury(II) tungstate(VI) top
Crystal data top
HgWO4F(000) = 744
Mr = 448.44Dx = 9.212 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -c_2ycCell parameters from 25 reflections
a = 11.3791 (4) Åθ = 23.4–46.5°
b = 6.00794 (15) ŵ = 82.80 mm1
c = 5.1456 (3) ÅT = 293 K
β = 113.202 (3)°Prism, colourless
V = 323.33 (2) Å30.06 × 0.03 × 0.03 mm
Z = 4
Data collection top
Enraf-Nonius TurboCAD-4
diffractometer
620 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR590Rint = 0.053
Graphite monochromatorθmax = 34.9°, θmin = 3.9°
ω/2θ scansh = 180
Absorption correction: gaussian
a grid of 12 x 20 x 48 was used (Reference?)
k = 99
Tmin = 0.078, Tmax = 0.172l = 78
1750 measured reflections3 standard reflections every 60 min
713 independent reflections intensity decay: none
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)] = 0.027 w = 1/[σ2(Fo2) + (0.0453P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.070(Δ/σ)max < 0.001
S = 1.10Δρmax = 3.10 e Å3
713 reflectionsΔρmin = 3.13 e Å3
31 parametersExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0031 (3)
Crystal data top
HgWO4V = 323.33 (2) Å3
Mr = 448.44Z = 4
Monoclinic, C2/cMo Kα radiation
a = 11.3791 (4) ŵ = 82.80 mm1
b = 6.00794 (15) ÅT = 293 K
c = 5.1456 (3) Å0.06 × 0.03 × 0.03 mm
β = 113.202 (3)°
Data collection top
Enraf-Nonius TurboCAD-4
diffractometer
620 reflections with I > 2σ(I)
Absorption correction: gaussian
a grid of 12 x 20 x 48 was used (Reference?)
Rint = 0.053
Tmin = 0.078, Tmax = 0.1723 standard reflections every 60 min
1750 measured reflections intensity decay: none
713 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02731 parameters
wR(F2) = 0.0700 restraints
S = 1.10Δρmax = 3.10 e Å3
713 reflectionsΔρmin = 3.13 e Å3
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
xyzUiso*/Ueq
W0.00.18680 (5)0.25000.00752 (12)
Hg0.25000.25000.00.01209 (13)
O10.0966 (4)0.0918 (8)0.0291 (9)0.0109 (8)
O20.1151 (5)0.3660 (10)0.4723 (11)0.0157 (8)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
W0.00837 (16)0.00798 (19)0.00758 (16)0.0000.00460 (11)0.000
Hg0.00990 (17)0.0150 (2)0.01329 (19)0.00413 (9)0.00661 (13)0.00038 (9)
O10.0100 (15)0.016 (2)0.0099 (15)0.0024 (14)0.0070 (13)0.0034 (14)
O20.018 (2)0.014 (2)0.015 (2)0.0049 (19)0.0063 (16)0.0003 (18)
Geometric parameters (Å, º) top
W—O21.733 (5)Hg—O2iv2.743 (5)
W—O11.953 (4)Hg—O1v3.131 (5)
W—O1i2.197 (5)W—Wi3.4143 (4)
Hg—O1ii2.044 (4)W—Hg3.5743 (1)
Hg—O2iii2.633 (5)W—Hgvi3.7082 (2)
O1—W—O1i69.42 (19)O2iii—Hg—O2iv68.71 (14)
O1i—W—O1vii80.8 (2)O1ii—Hg—O2iv85.33 (18)
O1—W—O1vii84.61 (13)O1—Hg—O2iii88.22 (17)
O2viii—W—O1i89.3 (2)O1ii—Hg—O2iii91.78 (17)
O2—W—O196.5 (2)O1—Hg—O2iv94.67 (18)
O2—W—O2viii103.2 (4)O2ix—Hg—O2iv111.29 (14)
O2viii—W—O1104.5 (2)O1ii—Hg—O1180.0 (2)
O1—W—O1viii146.0 (3)O2iii—Hg—O2ix180.0 (2)
O2—W—O1i163.4 (2)O2iv—Hg—O2x180.00 (19)
Symmetry codes: (i) x, y, z; (ii) x+1/2, y+1/2, z; (iii) x+1/2, y+1/2, z+1; (iv) x+1/2, y1/2, z+1/2; (v) x, y, z1/2; (vi) x1/2, y1/2, z; (vii) x, y, z+1/2; (viii) x, y, z+1/2; (ix) x, y, z1; (x) x, y+1, z1/2.

Experimental details

Crystal data
Chemical formulaHgWO4
Mr448.44
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)11.3791 (4), 6.00794 (15), 5.1456 (3)
β (°) 113.202 (3)
V3)323.33 (2)
Z4
Radiation typeMo Kα
µ (mm1)82.80
Crystal size (mm)0.06 × 0.03 × 0.03
Data collection
DiffractometerEnraf-Nonius TurboCAD-4
diffractometer
Absorption correctionGaussian
a grid of 12 x 20 x 48 was used (Reference?)
Tmin, Tmax0.078, 0.172
No. of measured, independent and
observed [I > 2σ(I)] reflections
1750, 713, 620
Rint0.053
(sin θ/λ)max1)0.806
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.027, 0.070, 1.10
No. of reflections713
No. of parameters31
Δρmax, Δρmin (e Å3)3.10, 3.13

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), LATCON (Schwarzenbach & King, 1999), XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top
W—O21.733 (5)Hg—O2iv2.743 (5)
W—O11.953 (4)Hg—O1v3.131 (5)
W—O1i2.197 (5)W—Wi3.4143 (4)
Hg—O1ii2.044 (4)W—Hg3.5743 (1)
Hg—O2iii2.633 (5)W—Hgvi3.7082 (2)
O1—W—O1i69.42 (19)O2iii—Hg—O2iv68.71 (14)
O1i—W—O1vii80.8 (2)O1ii—Hg—O2iv85.33 (18)
O1—W—O1vii84.61 (13)O1—Hg—O2iii88.22 (17)
O2viii—W—O1i89.3 (2)O1ii—Hg—O2iii91.78 (17)
O2—W—O196.5 (2)O1—Hg—O2iv94.67 (18)
O2—W—O2viii103.2 (4)O2ix—Hg—O2iv111.29 (14)
O2viii—W—O1104.5 (2)O1ii—Hg—O1180.0 (2)
O1—W—O1viii146.0 (3)O2iii—Hg—O2ix180.0 (2)
O2—W—O1i163.4 (2)O2iv—Hg—O2x180.00 (19)
Symmetry codes: (i) x, y, z; (ii) x+1/2, y+1/2, z; (iii) x+1/2, y+1/2, z+1; (iv) x+1/2, y1/2, z+1/2; (v) x, y, z1/2; (vi) x1/2, y1/2, z; (vii) x, y, z+1/2; (viii) x, y, z+1/2; (ix) x, y, z1; (x) x, y+1, z1/2.
 

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds