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

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 Mezica mine was refined in the noncentrosymmetric space group I using a Pb/Mo exchange disorder model with the approximate com­position Pb_0.94Mo_0.06[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.

Computing details

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).

lead(II) molybdate(VI)

Crystal data

Pb0.94Mo0.06[MoO4]	Dx = 6.671 Mg m^−3
Mr = 360.42	Mo Kα radiation, λ = 0.71070 Å
Tetragonal, I4	Cell parameters from 2580 reflections
Hall symbol: I -4	θ = 3.4–45.3°
a = 5.442 (1) Å	µ = 47.59 mm^−1
c = 12.1177 (14) Å	T = 294 K
V = 358.87 (5) Å^3	Chip, yellow
Z = 4	0.10 × 0.10 × 0.05 mm
F(000) = 614

Data collection

Rigaku R-AXIS RAPID diffractometer	335 independent reflections
Radiation source: normal-focus sealed tube	333 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.120
Detector resolution: 10.0000 pixels mm^-1	θmax = 25.3°, θmin = 3.4°
dtprofit.ref scans	h = −6→6
Absorption correction: numerical (NUMABS; Higashi, 2002)	k = −6→6
Tmin = 0.064, Tmax = 0.336	l = −14→14
6322 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0244P)^2 + 3.452P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.025	(Δ/σ)max = 0.049
wR(F^2) = 0.061	Δρmax = 0.71 e Å^−3
S = 1.16	Δρmin = −0.86 e Å^−3
335 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
30 parameters	Extinction coefficient: 0.0140 (8)
0 restraints	Absolute structure: Flack (1983), ???? Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.50 (6)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Pb1	0.5000	0.0000	0.2500	0.0213 (13)
Mo2	0.0000	0.0000	0.0000	0.022 (4)
Pb3	0.5000	0.5000	0.0000	0.025 (2)	0.881 (8)
Mo3	0.5000	0.5000	0.0000	0.025 (2)	0.119 (8)
Mo1	0.0000	0.5000	0.2500	0.018 (3)
O1	0.2344 (13)	−0.1372 (14)	0.0806 (6)	0.0302 (17)
O2	0.2338 (14)	0.3648 (14)	0.1697 (6)	0.0307 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pb1	0.021 (2)	0.021 (2)	0.022 (2)	0.000	0.000	0.000
Mo2	0.020 (6)	0.020 (6)	0.025 (7)	0.000	0.000	0.000
Pb3	0.023 (3)	0.023 (3)	0.027 (4)	0.000	0.000	0.000
Mo3	0.023 (3)	0.023 (3)	0.027 (4)	0.000	0.000	0.000
Mo1	0.016 (5)	0.016 (5)	0.021 (6)	0.000	0.000	0.000
O1	0.033 (5)	0.030 (4)	0.028 (4)	0.002 (3)	−0.005 (3)	0.004 (3)
O2	0.030 (5)	0.028 (4)	0.034 (4)	0.001 (3)	−0.003 (3)	0.011 (4)

Geometric parameters (Å, º)

Pb1—O1	2.619 (7)	Pb3—O2^viii	2.620 (7)
Pb1—O1^i	2.619 (7)	Pb3—O2^ix	2.620 (7)
Pb1—O1^ii	2.619 (7)	Pb3—O2	2.620 (7)
Pb1—O1^iii	2.619 (7)	Pb3—O1^v	2.635 (8)
Pb1—O2^i	2.643 (8)	Pb3—O1^x	2.635 (8)
Pb1—O2^ii	2.643 (8)	Pb3—O1^xi	2.635 (8)
Pb1—O2^iii	2.643 (8)	Pb3—O1^iii	2.635 (8)
Pb1—O2	2.643 (8)	Mo1—O2^xii	1.763 (8)
Mo2—O1^iv	1.772 (7)	Mo1—O2^xiii	1.763 (8)
Mo2—O1	1.772 (7)	Mo1—O2^xiv	1.763 (8)
Mo2—O1^v	1.772 (7)	Mo1—O2	1.763 (8)
Mo2—O1^vi	1.772 (7)	O1—Pb3^xv	2.635 (8)
Pb3—O2^vii	2.620 (7)
O1—Pb1—O1^i	127.9 (2)	O2^vii—Pb3—O2	76.6 (3)
O1—Pb1—O1^ii	127.9 (2)	O2^viii—Pb3—O2	128.0 (2)
O1^i—Pb1—O1^ii	76.8 (3)	O2^ix—Pb3—O2	128.0 (2)
O1—Pb1—O1^iii	76.8 (3)	O2^vii—Pb3—O1^v	149.2 (2)
O1^i—Pb1—O1^iii	127.9 (2)	O2^viii—Pb3—O1^v	67.4 (3)
O1^ii—Pb1—O1^iii	127.9 (2)	O2^ix—Pb3—O1^v	78.6 (2)
O1—Pb1—O2^i	149.2 (2)	O2—Pb3—O1^v	73.9 (3)
O1^i—Pb1—O2^i	67.9 (3)	O2^vii—Pb3—O1^x	73.9 (3)
O1^ii—Pb1—O2^i	78.4 (2)	O2^viii—Pb3—O1^x	78.6 (2)
O1^iii—Pb1—O2^i	73.6 (3)	O2^ix—Pb3—O1^x	67.4 (3)
O1—Pb1—O2^ii	73.6 (3)	O2—Pb3—O1^x	149.2 (2)
O1^i—Pb1—O2^ii	78.4 (2)	O1^v—Pb3—O1^x	136.5 (3)
O1^ii—Pb1—O2^ii	67.9 (3)	O2^vii—Pb3—O1^xi	78.6 (2)
O1^iii—Pb1—O2^ii	149.2 (2)	O2^viii—Pb3—O1^xi	149.2 (2)
O2^i—Pb1—O2^ii	136.8 (3)	O2^ix—Pb3—O1^xi	73.9 (3)
O1—Pb1—O2^iii	78.4 (2)	O2—Pb3—O1^xi	67.4 (3)
O1^i—Pb1—O2^iii	149.2 (2)	O1^v—Pb3—O1^xi	97.90 (11)
O1^ii—Pb1—O2^iii	73.6 (3)	O1^x—Pb3—O1^xi	97.90 (11)
O1^iii—Pb1—O2^iii	67.9 (3)	O2^vii—Pb3—O1^iii	67.4 (3)
O2^i—Pb1—O2^iii	97.79 (12)	O2^viii—Pb3—O1^iii	73.9 (3)
O2^ii—Pb1—O2^iii	97.79 (12)	O2^ix—Pb3—O1^iii	149.2 (2)
O1—Pb1—O2	67.9 (3)	O2—Pb3—O1^iii	78.6 (2)
O1^i—Pb1—O2	73.6 (3)	O1^v—Pb3—O1^iii	97.90 (11)
O1^ii—Pb1—O2	149.2 (2)	O1^x—Pb3—O1^iii	97.90 (11)
O1^iii—Pb1—O2	78.4 (2)	O1^xi—Pb3—O1^iii	136.5 (3)
O2^i—Pb1—O2	97.79 (12)	O2^xii—Mo1—O2^xiii	107.8 (2)
O2^ii—Pb1—O2	97.79 (12)	O2^xii—Mo1—O2^xiv	113.0 (5)
O2^iii—Pb1—O2	136.8 (3)	O2^xiii—Mo1—O2^xiv	107.8 (2)
O1^iv—Mo2—O1	107.7 (2)	O2^xii—Mo1—O2	107.8 (2)
O1^iv—Mo2—O1^v	113.1 (5)	O2^xiii—Mo1—O2	113.0 (5)
O1—Mo2—O1^v	107.7 (2)	O2^xiv—Mo1—O2	107.8 (2)
O1^iv—Mo2—O1^vi	107.7 (2)	Mo2—O1—Pb1	135.2 (4)
O1—Mo2—O1^vi	113.1 (5)	Mo2—O1—Pb3^xv	120.4 (4)
O1^v—Mo2—O1^vi	107.7 (2)	Pb1—O1—Pb3^xv	101.6 (2)
O2^vii—Pb3—O2^viii	128.0 (2)	Mo1—O2—Pb3	135.6 (4)
O2^vii—Pb3—O2^ix	128.0 (2)	Mo1—O2—Pb1	120.4 (3)
O2^viii—Pb3—O2^ix	76.6 (3)	Pb3—O2—Pb1	101.4 (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.