inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

On the symmetry of wulfenite (Pb[MoO4]) from Mežica (Slovenia)

aDepartment of Mineralogy, Eötvös Loránd University, Pázmány P. stny. 1/c, 1117 Budapest, Hungary, bInstitute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Pusztaszeri út 59–67, 1025 Budapest, Hungary, and cDepartment for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
*Correspondence e-mail: coraildiko@gmail.com

(Received 31 January 2011; accepted 26 April 2011; online 5 May 2011)

Wulfenite [lead(II) molybdate(VI)] is known as a scheelite structure in the I41/a space group. The structure of the unusual `hemimorphic' wulfenite crystals from the Mežica mine was refined in the noncentrosymmetric space group I[\overline{4}] using a Pb/Mo exchange disorder model with the approximate com­position Pb0.94Mo0.06[MoO4]. Pb atoms in the 2b positions are substituted by Mo at about 12%. The crystal is shown to be twinned by inversion. Hemimorphism may result from the short-range chemical ordering of the metal atoms at the 2b positions.

Comment

The mineral wulfenite (Pb[MoO4]) is a member of the scheelite group of minerals with the general formula ABO4, where the most abundant cations in the A and B positions are Ca, Sr, Ba and Pb, and Mo and W, respectively. Structure determinations for scheelite using single-crystal X-ray and neutron diffraction techniques indicated the I41/a space group (Zalkin & Templeton, 1964[Zalkin, A. & Templeton, D. H. (1964). J. Chem. Phys. 40, 501-504.]; Kay et al., 1964[Kay, M. I., Frazer, B. C. & Almodovar, I. (1964). J. Chem. Phys. 40, 504.]). Gürmen et al. (1971[Gürmen, E., Daniels, E. & King, J. S. (1971). J. Chem. Phys. 55, 1093-1097.]) studied the structure of scheelite-type minerals, such as SrMoO4, SrWO4, CaMoO4 and BaWO4, using neutron diffraction refinement and compared their O-atom positions. Arakcheeva & Chapuis (2008[Arakcheeva, A. & Chapuis, G. (2008). Acta Cryst. B64, 12-25.]) gave a comprehensive study of scheelite-like structures with both commensurate and incommensurate modulations in the site occupations and with substitutions along the 〈uv0〉 directions.

The first isotropic (Leciejewicz, 1965[Leciejewicz, J. (1965). Z. Kristallogr. 121, 158-164.]; neutron diffraction study) and anisotropic (Lugli et al., 1999[Lugli, C., Medici, L. & Saccardo, D. (1999). Neues Jahrb. Mineral. Monatsh. 6, 281-288.]; X-ray diffraction data) structure refinements of wulfenite from various localities resulted in the same symmetry. Recently, Hibbs et al. (2000[Hibbs, D. E., Jury, C. M., Leverett, P., Plimer, I. R. & Williams, P. A. (2000). Mineral. Mag. 64, 1057-1062.]) studied `hemihedral' (with polar symmetry along the c axis) tungstenian wulfenite crystals (Pb[Mo0.64W0.36O4]) from Chillagoe (Australia) and found different W–Mo distributions over the 2a and 2c tetra­hedral positions, responsible for the reduced I[\overline{4}] symmetry. Hemihedrism was inter­preted as a result of ordered substitution of Mo by W. Their conclusion may be subject to debate, since the difference in the R values resulting from isotropic structure refinement in the space group I41/a (R = 0.040) and from anisotropic refinement in the space group I[\overline{4}] (R = 0.038) is not very significant.

Hurlbut (1955[Hurlbut, C. S. (1955). Am. Mineral. 40, 857-860.]) first described two types of unusual `hemimorphic' wulfenite crystals from the Mežica mine (Slovenia) showing two habits: (i) pyramidal crystals indicating polar character on the [001] axis; and (ii) tabular crystals twinned on {00[\overline{1}]}. Based on their morphology and on etch and piezoelectric tests, he suggested that wulfenite from the Mežica mine crystallizes with tetra­gonal–pyramidal (4) symmetry. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) microdiffraction studies of these hemimorphic wulfenites from the Doroteja locality in the Mežica mine imply I4 (acentric tetra­gonal–pyramidal) symmetry (Zavašnik et al., 2010[Zavašnik, J., Rečnik, A., Samardžija, Z., Meden, A. & Dódony, I. (2010). Acta Mineral. Petrogr. Abstr. Ser. 6, 727.]). As a result of this lower symmetry, Rečnik (2010[Rečnik, A. (2010). In Minerals of the Lead and Zinc Ore Deposit Mežica. Ljubljana: Bode Vlg.]) explained a new law of basal inversion twinning, the so-called Doroteja Law, macroscopically observable in wulfenite crystals from this locality. These hemimorphic wulfenite crystals are the subject of this work.

Most of the previous structural studies indicated the space group I41/a for wulfenite. In contrast, many intense reflections in our data set violate the extinction rules of this symmetry, e.g. for 00l the l = 2n (with l values up to ±22) reflections, and several hk0 reflections (hk ≠ 2n), are evident. Experimentally, only the I-centring is proven (h + k + l = 2n). The space groups I4, I4/m, I[\overline{4}], Imm2, I4/mmm and I2/m were checked in structure refinements, as well as I41/a. Except for I[\overline{4}], the best R values resulting from the refinements in the above space groups converged to only about R = 0.07–0.08.

In the I[\overline{4}] space group, racemic twinning by merohedry was indicated as early as the isotropic refinement stage. The volume ratio of the twinned pair refined to 0.50 (6). The Pb and Mo cations were both allocated to two Wyckoff sites (Table 1[link]). The Pb sites at the 2b positions proved to be substituted by ∼12% Mo, which corresponds to the composition Pb0.94Mo0.06[MoO4]. The final anisotropic refinement converged to acceptably low R values for 30 parameters and no restraints. The resulting Pb:Mo ratio is within the range of the quantified energy-dispersive X-ray spectroscopy (EDS) data, the considered uncertainties and the different sample volumes. Final atomic parameters are listed in Table 1[link].

Besides the explanation of Pb/Mo substitution, the difference between the occupancy of the 2b and 2d Pb positions (and the potentially minor difference between the 2a and 2c Mo positions) could also be regarded as vacancies, which would also be in line with the Pb > Mo content observed from the EDS analyses. However, our X-ray model refinement, based on Pb/Mo substitution at the 2b site, resulted in consistently lower R, wR2 and S values (by about 0.005–0.01%) and also in lower residual densities at the metal sites.

Relevant bond distances for both I41/a Monte Cengio wulfenite (Lugli et al., 1999[Lugli, C., Medici, L. & Saccardo, D. (1999). Neues Jahrb. Mineral. Monatsh. 6, 281-288.]) and I[\overline{4}] Mežica wulfenite are listed for comparison in Table 2[link]. Although the degree of freedom in the space group I[\overline{4}] is higher than that in I41/a, the corresponding atomic distances and bond angles in the MoO4 and PbO8 groups in both the Mežica wulfenite and wulfenites with I41/a symmetry are identical within the known s.u. criteria. The hemimorphism of the Mežica wulfenite (cf. Fig. 1[link]) may be inter­preted as a result of ordering.

[Figure 1]
Figure 1
Polyhedral representation of Mežica wulfenite, projected along the b axis.

Experimental

A small single-crystal chip was carefully selected as a good scattering sample for experiments at T = 294 K. EDS analyses were measured on 100–200 nm sized wulfenite crystals using a Technai G2 X-Twin 200 kV analytical TEM. Besides Pb and Mo, the O content was also measured. The measured Pb:Mo ratios were close to 1 [atoms per formula unit (apfu) for Pb = 0.98 (4)]. These values are consistent with the ∼12% substitution in the 2b Pb site. A slight correlation was observed between the resolution of the data and the refined substitution at the 2b Pb site (at 0.6 Å resolution the substitution at the 2b site is ∼4%, while at 0.83 Å resolution it is ∼12%). Such virtual resolution dependence of the composition might be easily inter­preted in terms of the clearly deficient scattering model at a higher than usual (0.6 Å) resolution. Here, the dominant scattering of the core electrons and the use of spherical scattering factors yield an over-weighted spherical scattering model. The disorder-dependent smearing of the electron densities, as well as the deformation density due to valence and higher-orbital electron densities, thus logically provide somewhat lower populations than at a lower (0.83 Å) resolution.

Finally, we note that this model describes a twinned and disordered crystal using a discrete substitution site. This disorder model itself is only an approximation, as other Wyckoff sites might also contain minute contamination of, for example, chalcogenide elements.

Crystal data
  • Pb0.94Mo0.06[MoO4]

  • Mr = 360.42

  • Tetragonal, [I \overline 4]

  • a = 5.442 (1) Å

  • c = 12.1177 (14) Å

  • V = 358.87 (5) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 47.59 mm−1

  • T = 294 K

  • 0.10 × 0.10 × 0.05 mm

Data collection
  • Rigaku R-AXIS RAPID diffractometer

  • Absorption correction: numerical (NUMABS; Higashi, 2002[Higashi, T. (2002). NUMABS. Rigaku Corporation, Tokyo, Japan.]) Tmin = 0.064, Tmax = 0.336

  • 6322 measured reflections

  • 335 independent reflections

  • 333 reflections with I > 2σ(I)

  • Rint = 0.120

Refinement
  • R[F2 > 2σ(F2)] = 0.025

  • wR(F2) = 0.061

  • S = 1.16

  • 335 reflections

  • 30 parameters

  • Δρmax = 0.71 e Å−3

  • Δρmin = −0.86 e Å−3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), with 156 Friedel pairs

  • Flack parameter: 0.50 (6)

Table 1
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

  Wyckoff position x y z Uiso*/Ueq
Pb1 2d 0.5000 0.0000 0.2500 0.0213 (13)
Mo1 2c 0.0000 0.5000 0.2500 0.018 (3)
Mo2 2a 0.0000 0.0000 0.0000 0.022 (4)
Pb3 2b 0.5000 0.5000 0.0000 0.025 (2)
Mo3 2b 0.5000 0.5000 0.0000 0.025 (2)
O1 8g 0.2344 (13) −0.1372 (14) 0.0806 (6) 0.0302 (17)
O2 8g 0.2338 (14) 0.3648 (14) 0.1697 (6) 0.0307 (17)
†Occupancy = 0.881 (8).
‡Occupancy = 0.119 (8).

Table 2
Pb—O and Mo—O bond lengths (Å)

  This work Lugli et al. (1999)[Lugli, C., Medici, L. & Saccardo, D. (1999). Neues Jahrb. Mineral. Monatsh. 6, 281-288.]
Pb1—O1 2.619 (7) 2.611 (3)
Pb1—O2 2.643 (8) 2.636 (3)
Mo2—O1 1.772 (7) 1.769 (3)
Pb3—O2 2.620 (7) 2.611 (3)
Pb3—O1i 2.635 (8) 2.636 (3)
Mo1—O2 1.763 (8) 1.769 (3)
Symmetry code: (i) x, y + 1, z.

Racemic twinning was indicated during the isotropic refinement and the volume ratio of the twin pairs was refined to 0.50 (6). All atoms were treated anisotropically. An extinction parameter was also refined, and an occupancy constraint was applied for the 2b site.

Data collection: CrystalClear (Rigaku, 2008[Rigaku (2008). CrystalStructure. Rigaku Corporation, The Woodlands, Texas, USA.]); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

The mineral wulfenite (Pb[MoO4]) is a member of the scheelite group of minerals with the general formula ABO4, where the most abundant cations in the A and the B positions are Ca, Sr, Ba and Pb, and Mo and W, respectively. Structure determinations for scheelite using single-crystal X-ray and neutron diffraction techniques indicated the I41/a space group (Zalkin & Templeton, 1964; Kay et al., 1964). Gürmen et al. (1971) studied the structure of scheelite-type minerals such as SrMoO4, SrWO4, CaMo4 and BaWO4 using neutron diffraction refinement, and compared their O-atom positions. Arakcheeva & Chapuis (2008) gave a comprehensive study of scheelite-like structures with both commensurate and incommensurate modulations in the site occupations and with substitutions along the <uv0> directions.

The first isotropic (Leciejewicz, 1965; neutron diffraction study) and anisotropic (Lugli et al., 1999; X-ray diffraction data) structure refinements of wulfenite from various localities resulted in the same symmetry. Recently, Hibbs et al. (2000) studied `hemihedral' (with polar symmetry along its c axis) tungstenian wulfenite crystals (Pb[Mo0.64W0.36O4]) from Chillagoe (Australia) and found different W—Mo distribution over the 2a and 2c tetrahedral positions, responsible for the reduced I4 symmetry. Hemihedrism was interpreted as a result of ordered substitution of Mo by W. Their conclusion may be subject to debate, since the difference in the R values resulting from isotropic structure refinement in space group I41/a (R = 0.040) and from anisotropic refinement in space group I4 (R = 0.038) is not very significant.

Hurlbut (1955) first described two types of unusual `hemimorphic' wulfenite crystals from the Mežica mine (Slovenia) showing two habits: (i) pyramidal crystals indicating polar character on the [001] axis; (ii) tabular crystals twinned on {001}. Based on their morphology and on etch and piezoelectric tests, he suggested that wulfenite from the Mežica mine crystallizes in tetragonal–pyramidal (4) symmetry. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) microdiffraction studies of these hemimorphic wulfenites from the Doroteja locality in the Mežica mine imply I4 (acentric tetragonal pyramidal) symmetry (Zavašnik et al., 2010). As a result of this lower symmetry, Rečnik (2010) explained a new law of basal inversion twinning, the so-called Doroteja Law, macroscopically observable in wulfenite crystals from this locality. These hemimorphic wulfenite crystals are the subject of this work.

Most of the previous structural studies indicated the space group I41/a for wulfenite. In contrast, many intense reflections in our data set violate the extinction rules of this symmetry, e.g. for 00l the l = 2n (with l values up to ±22) reflections, and several hk0 reflections (h,k ≠ 2n), are evident. Experimentally, only the I-centring is proven (h + k + l = 2n). The space groups I4, I4/m, I4, Imm2, I4/mmm and I2/m were checked in structure refinements, as well as I41/a. Except for I4, the best R values resulting from the refinements in the above space groups converged to only about R = 0.07–0.08.

In the I4 space group, racemic twinning by merohedry was indicated as early as the isotropic refinement stage. The volume ratio of the twinned pair refined to 0.50 (6). Both Pb and Mo cations were allocated to two Wyckoff sites (Table 1). The Pb sites at the 2b positions proved to be substituted by ~12% Mo, which corresponds to the composition Pb0.94Mo0.06[MoO4]. The final anisotropic refinement converged to acceptably low R values for 30 parameters and no restraints. The resulting Pb:Mo ratio is within the range of the quantified energy-dispersive X-ray spectroscopy (EDS) data, the considered uncertainties and the different sample volumes. Final atomic parameters are listed in Table 1.

Besides the explanation of Pb/Mo substitution, the difference between the occupancy of the 2b and 2d Pb positions (and the potentially minor difference between the 2a and 2c Mo positions) could also be regarded as vacancies, which would also be in line with the Pb > Mo content observed from the EDS analyses. However, our X-ray model refinement, based on Pb/Mo substitution at the 2b site, resulted in consistently lower R, wR2 and S values (by about 0.005–0.01%) and also in lower residual densities at the metal sites.

Relevant bond distances for both I41/a wulfenite from Monte Cengio (Lugli et al., 1999) and I4 Mežica wulfenite are listed for comparison in Table 2. Although the degree of freedom in space group I4 is higher than that in I41/a, the corresponding atomic distances and bond angles in the MoO4 and PbO8 groups in both the Mežica wulfenite and wulfenites with I41/a symmetry are identical within the known s.u. criteria. The hemimorphism of the Mežica wulfenite (cf. Fig. 1) may be interpreted as a result of ordering.

Related literature top

For related literature, see: Arakcheeva & Chapuis (2008); Gürmen et al. (1971); Hibbs et al. (2000); Hurlbut (1955); Kay et al. (1964); Leciejewicz (1965); Lugli et al. (1999); Rečnik (2010); Zalkin & Templeton (1964); Zavašnik et al. (2010).

Experimental top

A small single-crystal chip was carefully selected from many as a good scattering sample for experiments at T = 294 K. EDS analyses were measured on 100–200 nm sized wulfenite crystals using a Technai G2 X-Twin 200 kV analytical TEM. Besides the Pb and Mo, the O content was also measured. The measured Pb:Mo ratios were close to 1 [atoms per formula unit (apfu) for Pb = 0.98 (4)]. These values are consistent with the ~12% substitution in the 2b Pb site. A slight correlation was observed between the resolution of the data and the refined substitution at the 2b Pb site (at 0.6 Å resolution, the substitution at the 2b site is ~4%, while at 0.83 Å resolution it is ~12%). Such virtual resolution dependence of the composition might be easily interpreted in terms of the clearly deficient scattering model at a higher than usual (0.6 Å) resolution. Here, the dominant scattering of the core electrons and the use of spherical scattering factors yield an over-weighted spherical scattering model. The disorder-dependent smearing of the electron densities, as well as the deformation density due to valence and higher-orbital electron densities, thus logically provide somewhat lower populations than at a lower (0.83 Å) resolution.

Finally, we note that this model describes a twinned and disordered crystal using a discrete substitution site. This disorder model itself is only an approximation, as other Wyckoff sites might also contain minute contamination of e.g. chalcogenide elements.

Refinement top

Racemic twinning was indicated during the isotropic refinement and the volume ratio of the twin pairs was refined to 0.50 (6). All atoms were treated anisotropically. An extinction parameter was also refined, and an occupancy constraint was applied for the 2b site.

Computing details top

Data collection: CrystalClear (Rigaku, 2008); cell refinement: CrystalClear (Rigaku, 2008); data reduction: CrystalClear (Rigaku, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Polyhedral representation of Mežica wulfenite, projected along the b axis.
lead(II) molybdate(VI) top
Crystal data top
Pb0.94Mo0.06[MoO4]Dx = 6.671 Mg m3
Mr = 360.42Mo Kα radiation, λ = 0.71070 Å
Tetragonal, I4Cell parameters from 2580 reflections
Hall symbol: I -4θ = 3.4–45.3°
a = 5.442 (1) ŵ = 47.59 mm1
c = 12.1177 (14) ÅT = 294 K
V = 358.87 (5) Å3Chip, yellow
Z = 40.10 × 0.10 × 0.05 mm
F(000) = 614
Data collection top
Rigaku R-AXIS RAPID
diffractometer
335 independent reflections
Radiation source: normal-focus sealed tube333 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.120
Detector resolution: 10.0000 pixels mm-1θmax = 25.3°, θmin = 3.4°
dtprofit.ref scansh = 66
Absorption correction: numerical
(NUMABS; Higashi, 2002)
k = 66
Tmin = 0.064, Tmax = 0.336l = 1414
6322 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0244P)2 + 3.452P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.025(Δ/σ)max = 0.049
wR(F2) = 0.061Δρmax = 0.71 e Å3
S = 1.16Δρmin = 0.86 e Å3
335 reflectionsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
30 parametersExtinction coefficient: 0.0140 (8)
0 restraintsAbsolute structure: Flack (1983), ???? Friedel pairs
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.50 (6)
Crystal data top
Pb0.94Mo0.06[MoO4]Z = 4
Mr = 360.42Mo Kα radiation
Tetragonal, I4µ = 47.59 mm1
a = 5.442 (1) ÅT = 294 K
c = 12.1177 (14) Å0.10 × 0.10 × 0.05 mm
V = 358.87 (5) Å3
Data collection top
Rigaku R-AXIS RAPID
diffractometer
335 independent reflections
Absorption correction: numerical
(NUMABS; Higashi, 2002)
333 reflections with I > 2σ(I)
Tmin = 0.064, Tmax = 0.336Rint = 0.120
6322 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0250 restraints
wR(F2) = 0.061Δρmax = 0.71 e Å3
S = 1.16Δρmin = 0.86 e Å3
335 reflectionsAbsolute structure: Flack (1983), ???? Friedel pairs
30 parametersAbsolute structure parameter: 0.50 (6)
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Pb10.50000.00000.25000.0213 (13)
Mo20.00000.00000.00000.022 (4)
Pb30.50000.50000.00000.025 (2)0.881 (8)
Mo30.50000.50000.00000.025 (2)0.119 (8)
Mo10.00000.50000.25000.018 (3)
O10.2344 (13)0.1372 (14)0.0806 (6)0.0302 (17)
O20.2338 (14)0.3648 (14)0.1697 (6)0.0307 (17)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Pb10.021 (2)0.021 (2)0.022 (2)0.0000.0000.000
Mo20.020 (6)0.020 (6)0.025 (7)0.0000.0000.000
Pb30.023 (3)0.023 (3)0.027 (4)0.0000.0000.000
Mo30.023 (3)0.023 (3)0.027 (4)0.0000.0000.000
Mo10.016 (5)0.016 (5)0.021 (6)0.0000.0000.000
O10.033 (5)0.030 (4)0.028 (4)0.002 (3)0.005 (3)0.004 (3)
O20.030 (5)0.028 (4)0.034 (4)0.001 (3)0.003 (3)0.011 (4)
Geometric parameters (Å, º) top
Pb1—O12.619 (7)Pb3—O2viii2.620 (7)
Pb1—O1i2.619 (7)Pb3—O2ix2.620 (7)
Pb1—O1ii2.619 (7)Pb3—O22.620 (7)
Pb1—O1iii2.619 (7)Pb3—O1v2.635 (8)
Pb1—O2i2.643 (8)Pb3—O1x2.635 (8)
Pb1—O2ii2.643 (8)Pb3—O1xi2.635 (8)
Pb1—O2iii2.643 (8)Pb3—O1iii2.635 (8)
Pb1—O22.643 (8)Mo1—O2xii1.763 (8)
Mo2—O1iv1.772 (7)Mo1—O2xiii1.763 (8)
Mo2—O11.772 (7)Mo1—O2xiv1.763 (8)
Mo2—O1v1.772 (7)Mo1—O21.763 (8)
Mo2—O1vi1.772 (7)O1—Pb3xv2.635 (8)
Pb3—O2vii2.620 (7)
O1—Pb1—O1i127.9 (2)O2vii—Pb3—O276.6 (3)
O1—Pb1—O1ii127.9 (2)O2viii—Pb3—O2128.0 (2)
O1i—Pb1—O1ii76.8 (3)O2ix—Pb3—O2128.0 (2)
O1—Pb1—O1iii76.8 (3)O2vii—Pb3—O1v149.2 (2)
O1i—Pb1—O1iii127.9 (2)O2viii—Pb3—O1v67.4 (3)
O1ii—Pb1—O1iii127.9 (2)O2ix—Pb3—O1v78.6 (2)
O1—Pb1—O2i149.2 (2)O2—Pb3—O1v73.9 (3)
O1i—Pb1—O2i67.9 (3)O2vii—Pb3—O1x73.9 (3)
O1ii—Pb1—O2i78.4 (2)O2viii—Pb3—O1x78.6 (2)
O1iii—Pb1—O2i73.6 (3)O2ix—Pb3—O1x67.4 (3)
O1—Pb1—O2ii73.6 (3)O2—Pb3—O1x149.2 (2)
O1i—Pb1—O2ii78.4 (2)O1v—Pb3—O1x136.5 (3)
O1ii—Pb1—O2ii67.9 (3)O2vii—Pb3—O1xi78.6 (2)
O1iii—Pb1—O2ii149.2 (2)O2viii—Pb3—O1xi149.2 (2)
O2i—Pb1—O2ii136.8 (3)O2ix—Pb3—O1xi73.9 (3)
O1—Pb1—O2iii78.4 (2)O2—Pb3—O1xi67.4 (3)
O1i—Pb1—O2iii149.2 (2)O1v—Pb3—O1xi97.90 (11)
O1ii—Pb1—O2iii73.6 (3)O1x—Pb3—O1xi97.90 (11)
O1iii—Pb1—O2iii67.9 (3)O2vii—Pb3—O1iii67.4 (3)
O2i—Pb1—O2iii97.79 (12)O2viii—Pb3—O1iii73.9 (3)
O2ii—Pb1—O2iii97.79 (12)O2ix—Pb3—O1iii149.2 (2)
O1—Pb1—O267.9 (3)O2—Pb3—O1iii78.6 (2)
O1i—Pb1—O273.6 (3)O1v—Pb3—O1iii97.90 (11)
O1ii—Pb1—O2149.2 (2)O1x—Pb3—O1iii97.90 (11)
O1iii—Pb1—O278.4 (2)O1xi—Pb3—O1iii136.5 (3)
O2i—Pb1—O297.79 (12)O2xii—Mo1—O2xiii107.8 (2)
O2ii—Pb1—O297.79 (12)O2xii—Mo1—O2xiv113.0 (5)
O2iii—Pb1—O2136.8 (3)O2xiii—Mo1—O2xiv107.8 (2)
O1iv—Mo2—O1107.7 (2)O2xii—Mo1—O2107.8 (2)
O1iv—Mo2—O1v113.1 (5)O2xiii—Mo1—O2113.0 (5)
O1—Mo2—O1v107.7 (2)O2xiv—Mo1—O2107.8 (2)
O1iv—Mo2—O1vi107.7 (2)Mo2—O1—Pb1135.2 (4)
O1—Mo2—O1vi113.1 (5)Mo2—O1—Pb3xv120.4 (4)
O1v—Mo2—O1vi107.7 (2)Pb1—O1—Pb3xv101.6 (2)
O2vii—Pb3—O2viii128.0 (2)Mo1—O2—Pb3135.6 (4)
O2vii—Pb3—O2ix128.0 (2)Mo1—O2—Pb1120.4 (3)
O2viii—Pb3—O2ix76.6 (3)Pb3—O2—Pb1101.4 (3)
Symmetry codes: (i) y+1/2, x+1/2, z+1/2; (ii) y+1/2, x1/2, z+1/2; (iii) x+1, y, z; (iv) y, x, z; (v) y, x, z; (vi) x, y, z; (vii) x+1, y+1, z; (viii) y+1, x, z; (ix) y, x+1, z; (x) y+1, x+1, z; (xi) x, y+1, z; (xii) y+1/2, x+1/2, z+1/2; (xiii) x, y+1, z; (xiv) y1/2, x+1/2, z+1/2; (xv) x, y1, z.

Experimental details

Crystal data
Chemical formulaPb0.94Mo0.06[MoO4]
Mr360.42
Crystal system, space groupTetragonal, I4
Temperature (K)294
a, c (Å)5.442 (1), 12.1177 (14)
V3)358.87 (5)
Z4
Radiation typeMo Kα
µ (mm1)47.59
Crystal size (mm)0.10 × 0.10 × 0.05
Data collection
DiffractometerRigaku R-AXIS RAPID
diffractometer
Absorption correctionNumerical
(NUMABS; Higashi, 2002)
Tmin, Tmax0.064, 0.336
No. of measured, independent and
observed [I > 2σ(I)] reflections
6322, 335, 333
Rint0.120
(sin θ/λ)max1)0.601
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.025, 0.061, 1.16
No. of reflections335
No. of parameters30
Δρmax, Δρmin (e Å3)0.71, 0.86
Absolute structureFlack (1983), ???? Friedel pairs
Absolute structure parameter0.50 (6)

Computer programs: CrystalClear (Rigaku, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
Wyckoff positionxyzUiso*/UeqOcc. (<1)
Pb12d0.50000.00000.25000.0213 (13)
Mo12c0.00000.50000.25000.018 (3)
Mo22a0.00000.00000.00000.022 (4)
Pb32b0.50000.50000.00000.025 (2)0.881 (8)
Mo32b0.50000.50000.00000.025 (2)0.119 (8)
O18g0.2344 (13)-0.1372 (14)0.0806 (6)0.0302 (17)
O28g0.2338 (14)0.3648 (14)0.1697 (6)0.0307 (17)
Pb—O and Mo—O bond lengths (Å) top
This workLugli <it> et al.</it> (1999)
Pb1—O12.619 (7)2.611 (3)
Pb1—O22.643 (8)2.636 (3)
Mo2—O11.772 (7)1.769 (3)
Pb3—O22.620 (7)2.611 (3)
Pb3—O12.635 (8)2.636 (3)
Mo1—O21.763 (8)1.769 (3)
Symmetry codes: (i) y + 1/2, -x + 1/2, -z + 1/2; (ii) -y + 1/2, x - 1/2, -z + 1/2; (iii) -x + 1, -y, z; (iv) y, -x, -z; (v) -y, x, -z; (vi) -x, -y, z; (vii) -x + 1, -y + 1, z; (viii) -y + 1, x, -z; (ix) y, -x + 1, -z; (x) y + 1, -x + 1, -z; (xi) x, y + 1, z; (xii) -y + 1/2, x + 1/2, -z + 1/2; (xiii) -x, -y + 1, z; (xiv) y - 1/2, -x + 1/2, -z + 1/2; (xv) x, y - 1, z.
 

Acknowledgements

The authors express their sincere thanks to Alajos Kálmán and László Párkányi for their helpful comments and suggestions, and to Tamás Holczbauer for his help. We also thank the HAS CRC for carrying out the X-ray data collection. Financial support, administered through OTKA grant Nos. 68562 and K-75869 and the ARRS L1-2232 project, is gratefully acknowledged.

References

First citationArakcheeva, A. & Chapuis, G. (2008). Acta Cryst. B64, 12–25.  Web of Science CrossRef IUCr Journals
First citationFlack, H. D. (1983). Acta Cryst. A39, 876–881.  CrossRef CAS Web of Science IUCr Journals
First citationGürmen, E., Daniels, E. & King, J. S. (1971). J. Chem. Phys. 55, 1093–1097.
First citationHibbs, D. E., Jury, C. M., Leverett, P., Plimer, I. R. & Williams, P. A. (2000). Mineral. Mag. 64, 1057–1062.  CrossRef CAS
First citationHigashi, T. (2002). NUMABS. Rigaku Corporation, Tokyo, Japan.
First citationHurlbut, C. S. (1955). Am. Mineral. 40, 857–860.  CAS
First citationKay, M. I., Frazer, B. C. & Almodovar, I. (1964). J. Chem. Phys. 40, 504.  CrossRef
First citationLeciejewicz, J. (1965). Z. Kristallogr. 121, 158–164.  CrossRef CAS
First citationLugli, C., Medici, L. & Saccardo, D. (1999). Neues Jahrb. Mineral. Monatsh. 6, 281–288.
First citationRečnik, A. (2010). In Minerals of the Lead and Zinc Ore Deposit Mežica. Ljubljana: Bode Vlg.
First citationRigaku (2008). CrystalStructure. Rigaku Corporation, The Woodlands, Texas, USA.
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals
First citationSpek, A. L. (2009). Acta Cryst. D65, 148–155.  Web of Science CrossRef CAS IUCr Journals
First citationZalkin, A. & Templeton, D. H. (1964). J. Chem. Phys. 40, 501–504.  CrossRef CAS
First citationZavašnik, J., Rečnik, A., Samardžija, Z., Meden, A. & Dódony, I. (2010). Acta Mineral. Petrogr. Abstr. Ser. 6, 727.

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