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Mercury(II) tungstate powder, HgWO4, was prepared by boiling a mixture of HgO and H2WO4 in water. Rietveld refinements on neutron powder data showed that the monoclinic structure (C2/c) consists of zigzag chains of edge-sharing HgO6 and WO6 octahedra. The Hg atom lies on an inversion centre and the W atom lies on a twofold axis. The Hg atom forms two characteristic short collinear Hg-O bonds.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199013864/br1261sup1.cif
Contains datablocks hgwo, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108270199013864/br1261Isup2.rtv
Contains datablock I

Comment top

The structure determination of the title compound is part of a study of divalent metal ion tungstates (MWO4) (Åsberg Dahlborg & Svensson, 2000). These materials are of interest for their luminescent properties and find their applications as detector materials for high-energy radiation and particles (Blasse & Grabmaier, 1994). The high density (9.2 g cm-3) and strong absorption of high-energy radiation makes HgWO4 interesting for electromagnetic calorimetry applications.

HgWO4 has not been as thoroughly examined as the other tungstates but Swindells (1951) has previously reported the synthesis and emission spectra for HgWO4. Later Blasse & Heuvel (1974) investigated the luminescence properties further and compared them with other tungstates but no structure refinements have been carried out on HgWO4.

Most divalent metal ion tungstates (AWO4) belong to either the scheelite structure (Sillén & Nylander, 1943), if the radius of A is greater then 1 Å, or the wolframite structure (Keeling, 1957), if the radius of A is smaller then 1 Å. The radius of the Hg2+ ion is close to 1 Å and HgWO4 does not belong to either of the wolframite or the scheelite structure. The structure of HgMoO4 was published in 1973 (Jeitschko & Sleight, 1973) and is closely related to the wolframite structure. They also showed that HgWO4 belong to the same type structure but no structural data were published. Difficulties of growing single crystals and the combination of light and heavy atoms together with strong X-ray absorption promted us to use neutron powder diffraction and Rietveld refinements to get accurate structural parameters.

The structure of HgWO4 consists of zigzag chains of edge-sharing WO6 octahedra extending parallel to the c axis (Fig. 1). The O atoms form close-packed layers parallel to the yz plane. The stacking is close to cubic close-packing but adjacent ABC layers are slightly displaced relative to each other so that the fifth layer, B', corresponds to the A layer. Thus, the octahedral voids accommodating the Hg atoms are very distorted. As expected, mercury forms two short collinear Hg—O bonds with an Hg—O distance of 2.039 (4) Å. The other two pairs of Hg—O bonds are 2.627 (3) and 2.731 (3) Å, forming a very distorted octahedron. By edge-sharing, the HgO6 octahedra also form zigzag chains running along the c axis.

The structure of HgWO4 is closely related to the wolframite structure of the other d10 elements, ZnWO4 and CdWO4 (Åsberg Dahlborg & Svensson, 2000), since the polyhedra are interconnected in the same way. However, the coordination polyhedron around the Hg atom makes the HgWO4 structure different from Zn- and CdWO4. The O—Hg—O angles are all 180°, whereas the O—Zn—O and O—Cd—O angles are about 160° in ZnWO4 and CdWO4. The WO6 octahedra in the three structures are very similar. The WO6 octahedron in HgWO4, however, is more tetrahedral than in ZnWO4 and Cd.

Experimental top

The title compound was prepared by mixing equal amounts of HgO and H2WO4 in water. The mixture was boiled for a few minutes until the orange colour of HgO disappeared. The product was filtered and dried at room temperature. The resulting powder was pale yellow.

Refinement top

As HgWO4 is isostructural with HgMoO4 and the ionic radius of W is very close to that of Mo, the structural parameters of HgMoO4 were taken as starting parameters for the structural refinement of HgWO4. The program FULLPROF (Rodriguez-Carvajal, 1997) was used for refining the cell and structure. The profile shape was represented by a pseudo-Voigt function. Profile, lattice, structure parameters, zero-point shift, six background parameters and the scale factor were refined without correction for preferred orientation. Atomic displacements were assumed to be isotropic. WINPLOTR (Roisnel & Rodriguez-Carvajal, 1999) was used for plotting the powder diffractogram and ATOMS (Dowty, 1998) was used for the polyhedral representation. The weight function used in the refinements was 1/u2 where u is the s.u. for the observed intensities of each data point.

Computing details top

Data collection: Fullprof (Rodriguez-Carvajal, 1997); cell refinement: Fullprof; data reduction: Fullprof; program(s) used to solve structure: Fullprof; program(s) used to refine structure: Fullprof; molecular graphics: ATOMS (Dowty, 1998); software used to prepare material for publication: WinPLOTR (Roisnel and Rodriguez-Carvajal, 1999).

Figures top
[Figure 1] Fig. 1. Polyhedral representation of HgWO4, viewed along the c axis with b horizontal. The WO6 octahedra are grey and the HgO6 octahedra are white.
[Figure 2] Fig. 2. Comparison of observed (dots) and calculated (solid line) intensities for HgWO4. Tick marks below the diffractogram represent the allowed Bragg reflections. The difference intensities are located at the bottom of the figure.
mercury(II) tungstate top
Crystal data top
HgWO4V = 323.32 (4) Å3
Mr = 448.44Z = 4
Monoclinic, C2/cDx = 9.212 Mg m3
Hall symbol: -c_2ycNeutron radiation, λ = 1.470 Å
a = 11.3606 (8) ÅT = 295 K
b = 6.0125 (4) Åpale yellow
c = 5.1482 (4) Åcylinder, 10 × 10 mm
β = 113.159 (4)°Specimen preparation: Prepared at 373 K
Data collection top
Neutron powder
diffractometer
Data collection mode: transmission
Radiation source: neutron reactorScan method: step
Cu(220) monochromator2θmin = 12.0°, 2θmax = 139.92°, 2θstep = 0.08°
Specimen mounting: vanadium can
Refinement top
Refinement on InetExcluded region(s): 4 to 12 degrees, no Bragg peaks
Least-squares matrix: full with fixed elements per cycleProfile function: Pseudo-Voigt
Rp = 0.02827 parameters
Rwp = 0.035Weighting scheme based on measured s.u.'s
Rexp = 0.029(Δ/σ)max < 0.01
RBragg = 0.047Background function: polynomial function adjusted iteratively in each cycle
χ2 = 1.513Preferred orientation correction: none
1700 data points
Crystal data top
HgWO4β = 113.159 (4)°
Mr = 448.44V = 323.32 (4) Å3
Monoclinic, C2/cZ = 4
a = 11.3606 (8) ÅNeutron radiation, λ = 1.470 Å
b = 6.0125 (4) ÅT = 295 K
c = 5.1482 (4) Åcylinder, 10 × 10 mm
Data collection top
Neutron powder
diffractometer
Scan method: step
Specimen mounting: vanadium can2θmin = 12.0°, 2θmax = 139.92°, 2θstep = 0.08°
Data collection mode: transmission
Refinement top
Rp = 0.028χ2 = 1.513
Rwp = 0.0351700 data points
Rexp = 0.02927 parameters
RBragg = 0.047
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Hg0.250.2500.0096 (5)*
W00.1879 (8)0.250.0082 (14)*
O10.0966 (3)0.0918 (5)0.0279 (6)0.0065 (8)*
O20.1160 (3)0.3678 (5)0.4745 (7)0.0134 (9)*
Geometric parameters (Å, º) top
Hg—O12.039 (4)Hg—Hg3.9577 (2)
Hg—O22.627 (3)Hg—Hg3.9577 (2)
Hg—O22.731 (3)Hg—Wiii3.5690 (5)
W—O21.745 (4)Hg—W3.8064 (5)
W—O11.958 (4)Hg—O22.627 (3)
W—O1i2.201 (5)Hg—W3.712 (3)
Hg—W3.5690 (5)Hg—O12.039 (4)
Hg—Wi3.712 (3)Hg—O22.731 (3)
Hg—W3.8064 (5)W—O21.745 (4)
Hg—Hgii3.9577 (2)W—W3.425 (4)
W—Wi3.425 (4)W—O11.958 (4)
Hg—Hg3.9577 (2)W—O12.201 (5)
O1—Hg—O1iv180W—Hg—Hg68.99 (7)
O2—Hg—O2180W—Hg—Hg111.01 (7)
O2—Hg—O2180W—Hg—Hg58.83 (6)
W—Hg—W54.18 (7)Hg—Hg—Hg81.144 (6)
W—Hg—W56.08 (7)Hg—Hg—Hg98.856 (6)
W—Hg—Hg120.59 (3)Hg—Hg—Hg180
W—Hg—Hg124.65 (3)Hg—Hg—Hg81.144 (6)
W—Hg—Hg55.35 (3)Hg—W—Hg89.65 (10)
W—Hg—Hg59.41 (4)Hg—W—W64.32 (8)
W—Hg—Wiii123.92 (7)Hg—W—W59.85 (7)
W—Hg—W125.82 (7)Hg—W—Hg65.82 (3)
W—Hg—W180Hg—W—Hg63.51 (3)
O1v—Hg—O294.57 (12)O2—W—O2103.4 (3)
O1v—Hg—O288.10 (11)O2—W—O1104.30 (17)
O1v—Hg—O291.90 (11)O2—W—O196.83 (17)
O1v—Hg—O285.43 (12)O2—W—O189.39 (13)
O2—Hg—O268.73 (11)O2—W—O1163.3 (2)
O2—Hg—O2111.27 (11)Hg—W—W61.50 (4)
O2—Hg—O185.43 (12)Hg—W—W127.34 (9)
W—Hg—W88.476 (11)Hg—W—Hg90.346 (16)
W—Hg—Hg66.77 (6)Hg—W—Hg168.74 (14)
W—Hg—Hg122.92 (6)W—W—Hg125.12 (9)
W—Hg—Hg57.08 (6)W—W—W97.46 (15)
W—Hg—Hg113.23 (6)W—W—Hg64.07 (4)
W—Hg—Wiii91.524 (12)Hg—W—Hg167.98 (15)
W—Hg—W180O1—W—O1145.7 (3)
W—Hg—O2156.54 (10)O1—W—O169.25 (17)
W—Hg—W125.82 (6)O1—W—O184.45 (18)
W—Hg—Hg121.17 (6)O1—W—O180.37 (19)
Symmetry codes: (i) x, y, z; (ii) x, y, z+1/2; (iii) x+1/2, y+1/2, z; (iv) x+1/2, y+1/2, z; (v) x+1/2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaHgWO4
Mr448.44
Crystal system, space groupMonoclinic, C2/c
Temperature (K)295
a, b, c (Å)11.3606 (8), 6.0125 (4), 5.1482 (4)
β (°) 113.159 (4)
V3)323.32 (4)
Z4
Radiation typeNeutron, λ = 1.470 Å
µ (mm1)?
Specimen shape, size (mm)Cylinder, 10 × 10
Data collection
DiffractometerNeutron powder
diffractometer
Specimen mountingVanadium can
Data collection modeTransmission
Scan methodStep
2θ values (°)2θmin = 12.0 2θmax = 139.92 2θstep = 0.08
Refinement
R factors and goodness of fitRp = 0.028, Rwp = 0.035, Rexp = 0.029, RBragg = 0.047, χ2 = 1.513
No. of data points1700
No. of parameters27
No. of restraints?

Computer programs: Fullprof (Rodriguez-Carvajal, 1997), Fullprof, ATOMS (Dowty, 1998), WinPLOTR (Roisnel and Rodriguez-Carvajal, 1999).

Selected geometric parameters (Å, º) top
Hg—O12.039 (4)Hg—W3.5690 (5)
Hg—O22.627 (3)Hg—Wi3.712 (3)
Hg—O22.731 (3)Hg—W3.8064 (5)
W—O21.745 (4)Hg—Hgii3.9577 (2)
W—O11.958 (4)W—Wi3.425 (4)
W—O1i2.201 (5)
O1—Hg—O1iii180
Symmetry codes: (i) x, y, z; (ii) x, y, z+1/2; (iii) x+1/2, y+1/2, z.
 

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