Redetermination of Zn₂Mo₃O₈

The crystal structure of dizinc trimolybdenum(IV) octa­oxide, Zn₂Mo₃O₈, has been redetermined from single-crystal X-ray data. The structure has been reported previously based on neutron powder diffraction data [Hibble et al. (1999). Acta Cryst. B55, 683-697] and single-crystal data [McCarroll et al. (1957). J. Am. Chem. Soc. 79, 5410–5414; Ansell & Katz (1966) Acta Cryst. 21, 482–485]. The results of the current redetermination show an improvement in the precision of the structural and geometric parameters with all atoms refined with anisotropic displacement parameters. The crystal structure consists of distorted hexa­gonal-close-packed oxygen layers with stacking sequence abac along [001] and is held together by alternating zinc and molybdenum layers. The Zn atoms occupy both tetra­hedral and octa­hedral inter­stices with a ratio of 1:1. The Mo atoms occupy octa­hedral sites and form strongly bonded triangular clusters involving three MoO₆ octa­hedra that are each shared along two edges, forming a Mo₃O₁₃ unit. All atoms lie on special positions. The Zn atoms are in 2b Wyckoff positions with 3m. site symmetry, the Mo atoms are in 6c Wyckoff positions with . m. site symmetry and the O atoms are in 2a, 2b and 6c Wyckoff positions with 3m. and . m. site symmetries, respectively.

Related literature

The synthesis of Zn₂Mo₃O₈ is described by McCarroll et al. (1957). For previous reports of the crystal structure, see: McCarroll et al. (1957); Ansell & Katz (1966); Hibble et al. (1999). Zn₂Mo₃O₈ is isotypic with the mineral kamiokite, Fe₂Mo₃O₈ (Kanazawa & Sasaki, 1986). For other compounds containing Mo₃O₁₃ cluster units, see: Betteridge et al. (1984); Collins et al. (1989); Gall & Gougeon (2005); Gougeon & Gall (2007); McCarroll (1977); Torardi & McCarley (1985).

Experimental

Crystal data

• Zn₂Mo₃O₈

• M_r = 546.56

• Hexagonal, P 6₃ m c

• a = 5.7816 (2) Å

• c = 9.9345 (3) Å

• V = 287.59 (2) ų

• Z = 2

• Mo Kα radiation

• μ = 14.59 mm⁻¹

• T = 293 K

• 0.21 × 0.13 × 0.07 mm

Data collection

• Nonius KappaCCD diffractometer

• Absorption correction: analytical (de Meulenaer & Tompa, 1965) T_min = 0.048, T_max = 0.157

• 8536 measured reflections

• 790 independent reflections

• 778 reflections with I > 2σ(I)

• R_int = 0.023

Refinement

• R[F² > 2σ(F²)] = 0.013

• wR(F²) = 0.029

• S = 1.16

• 790 reflections

• 33 parameters

• 1 restraint

• Δρ_max = 0.97 e Å⁻³

• Δρ_min = −1.06 e Å⁻³

• Absolute structure: Flack (1983), 322 Friedel pairs

• Flack parameter: 0.155 (15)

Table 1
Selected bond lengths (Å)

Mo1—O1	1.9549 (14)
Mo1—O4	2.0286 (19)
Mo1—O2	2.0804 (10)
Mo1—O3	2.1415 (14)
Mo1—Mo1^i	2.5326 (2)
Zn1—O3^ii	1.963 (3)
Zn2—O1	2.0467 (18)
Zn2—O2^iii	2.1431 (16)
Symmetry codes: (i) -x+y, -x, z; (ii) x, y+1, z; (iii) .

Data collection: COLLECT (Nonius, 1998); cell refinement: COLLECT; data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Bergerhoff, 1996); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Comment

The M₂Mo₃O₈ compounds, where M is a divalent metal such as Mg, Zn, Fe, Co, Ni, Zn and Cd, were first synthesized by McCarroll et al. (1957). They presented the results of structure determination on Zn₂Mo₃O₈ from photographic data (R = 0.118). Later, a refinement of the structure was accomplished by Ansell & Katz (1966) with a R factor of 0.069. Among the above compounds, it is interesting to note that Fe₂Mo₃O₈ is a mineral known as kamiokite (Kanazawa & Sasaki, 1986). The main structural feature of Zn₂Mo₃O₈ is the occurrence of Mo₃O₁₃ cluster units sharing part of their oxygen atoms to form layers according to the connective formula Mo₃O₄O_6/2O_3/3. The oxygen atoms form an hexagonal-close-packing with a stacking sequence abac along [001] (Fig. 1). The Mo—Mo distance within the Mo₃ triangle (Fig. 2) is 2.5326 (2) Å which differs slightly from 2.524 (2) Å found previously and is equal to that found in the isotopic compound Fe₂Mo₃O₈ (2.5326 (5) Å). The Mo—O distances range from 1.9549 (14) to 2.1415 (14) Å compared to 1.928 (20) to 2.128 (30) Å in the previous determination based on single-crystal data (1.953 (4)–2.135 (4) in Fe₂Mo₃O₈). In our work, The ZnO₄ tetrahedra appear more regular with Zn—O distances of 1.963 (3) and 1.9687 (15) Å instead of 1.98 (1) and 1.99 (3) Å while the ZnO₆ octahedra are more distorted with Zn—O distances of 2.0467 (18) and 2.1431 (16) Å compared to 2.072 (20) and 2.123 (10) Å observed by Ansell & Katz (1966).

For other compounds containing Mo₃O₁₃ cluster units, see: Betteridge et al. (1984); Collins et al. (1989); Gall & Gougeon (2005); Gougeon & Gall (2007); McCarroll (1977); Torardi & McCarley (1985).

Related literature

The synthesis of Zn₂Mo₃O₈ is described by McCarroll et al. (1957). For previous reports of the crystal structure, see: McCarroll et al. (1957); Ansell & Katz (1966); Hibble et al. (1999). Zn₂Mo₃O₈ is isotypic with the mineral kamiokite, Fe₂Mo₃O₈ (Kanazawa & Sasaki, 1986). For other compounds containing Mo₃O₁₃ cluster units, see: Betteridge et al. (1984); Collins et al. (1989); Gall & Gougeon (2005); Gougeon & Gall (2007); McCarroll (1977); Torardi & McCarley (1985).

S2. Experimental

Single crystals of Zn₂Mo₃O₈ were obtained by the reaction of ZnO, MoO₃, and Mo. The initial mixture (ca 5 g) was cold pressed and loaded into a molybdenum crucible, which was sealed under a low argon pressure using an arc welding system. The charge was heated at the rate of 300 K/h up to 1573 K, the temperature which was held for 48 h, then cooled at 100 K/h down to 1373 K and finally cooled down to room temperature by switching off the furnace.

S3. Refinement

The highest peak and the deepest hole are located 0.68 Å and 0.74 Å from Mo1. The crystal under investigation was racemically twinned with a twin component ratio of 0.155 (15):0.845 (155).

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: COLLECT (Nonius, 1998); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Bergerhoff, 1996); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. : View of Zn2Mo3O8 along [110].
	Fig. 2. : Plot showing the atom-numbering scheme of the Mo3O13 cluster unit. Displacement ellipsoids are drawn at the 97% probability level.

dizinc trimolybdenum(IV) octaoxide

Crystal data

Zn2Mo3O8	Dx = 6.312 Mg m^−3
Mr = 546.56	Mo Kα radiation, λ = 0.71069 Å
Hexagonal, P63mc	Cell parameters from 6245 reflections
Hall symbol: P 6c -2c	θ = 0.9–44.0°
a = 5.7816 (2) Å	µ = 14.59 mm^−1
c = 9.9345 (3) Å	T = 293 K
V = 287.59 (2) Å^3	Irregular block, black
Z = 2	0.21 × 0.13 × 0.07 mm
F(000) = 500

Data collection

Nonius KappaCCD diffractometer	790 independent reflections
Radiation source: fine-focus sealed tube	778 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ϕ scans (κ = 0) + additional ω scans	θmax = 44.0°, θmin = 4.1°
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	h = −11→7
Tmin = 0.048, Tmax = 0.157	k = −11→11
8536 measured reflections	l = −16→19

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0117P)^2 + 0.2665P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.013	(Δ/σ)max = 0.001
wR(F^2) = 0.029	Δρmax = 0.97 e Å^−3
S = 1.16	Δρmin = −1.06 e Å^−3
790 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
33 parameters	Extinction coefficient: 0.0306 (13)
1 restraint	Absolute structure: Flack (1983), 322 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.155 (15)

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.

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 (Ų)

	x	y	z	Uiso*/Ueq
Mo1	−0.29203 (3)	−0.146014 (13)	−0.925032 (13)	0.00373 (3)
Zn1	−0.6667	0.6667	−0.62348 (6)	0.00671 (7)
Zn2	−0.3333	0.3333	−0.68932 (6)	0.00606 (7)
O1	−0.16669 (16)	0.16669 (16)	−0.8086 (2)	0.00588 (19)
O2	−0.51182 (15)	−0.0236 (3)	−1.04041 (16)	0.0055 (2)
O3	−0.6667	−0.3333	−0.8210 (3)	0.0054 (4)
O4	0.0000	0.0000	−1.0666 (3)	0.0057 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.00333 (5)	0.00389 (4)	0.00377 (5)	0.00166 (2)	0.00017 (5)	0.00008 (2)
Zn1	0.00746 (10)	0.00746 (10)	0.00521 (15)	0.00373 (5)	0.000	0.000
Zn2	0.00647 (10)	0.00647 (10)	0.00525 (15)	0.00323 (5)	0.000	0.000
O1	0.0061 (4)	0.0061 (4)	0.0052 (5)	0.0028 (4)	0.0007 (2)	−0.0007 (2)
O2	0.0048 (3)	0.0056 (5)	0.0066 (6)	0.0028 (2)	0.0005 (2)	0.0011 (4)
O3	0.0063 (5)	0.0063 (5)	0.0038 (8)	0.0031 (2)	0.000	0.000
O4	0.0068 (5)	0.0068 (5)	0.0036 (8)	0.0034 (3)	0.000	0.000

Geometric parameters (Å, º)

Mo1—O1	1.9549 (14)	Zn1—O2^v	1.9687 (15)
Mo1—O1^i	1.9549 (14)	Zn1—O2^vi	1.9687 (15)
Mo1—O4	2.0286 (19)	Zn1—O2^vii	1.9687 (15)
Mo1—O2	2.0804 (10)	Zn2—O1	2.0467 (18)
Mo1—O2^ii	2.0804 (10)	Zn2—O1^viii	2.0467 (18)
Mo1—O3	2.1415 (14)	Zn2—O1^ix	2.0467 (18)
Mo1—Mo1^iii	2.5326 (2)	Zn2—O2^x	2.1431 (16)
Mo1—Mo1^i	2.5326 (2)	Zn2—O2^xi	2.1431 (16)
Zn1—O3^iv	1.963 (3)	Zn2—O2^vii	2.1431 (16)
O1—Mo1—O1^i	95.38 (11)	O1—Zn2—O1^viii	89.84 (8)
O1—Mo1—O4	100.30 (5)	O1—Zn2—O1^ix	89.84 (8)
O1^i—Mo1—O4	100.30 (5)	O1^viii—Zn2—O1^ix	89.84 (8)
O1—Mo1—O2	91.06 (7)	O1—Zn2—O2^x	96.01 (5)
O1^i—Mo1—O2	166.69 (5)	O1^viii—Zn2—O2^x	171.73 (8)
O4—Mo1—O2	89.96 (6)	O1^ix—Zn2—O2^x	96.01 (5)
O1—Mo1—O2^ii	166.69 (5)	O1—Zn2—O2^xi	96.01 (5)
O1^i—Mo1—O2^ii	91.06 (7)	O1^viii—Zn2—O2^xi	96.01 (5)
O4—Mo1—O2^ii	89.96 (6)	O1^ix—Zn2—O2^xi	171.73 (7)
O2—Mo1—O2^ii	80.41 (8)	O2^x—Zn2—O2^xi	77.60 (7)
O1—Mo1—O3	89.76 (6)	O1—Zn2—O2^vii	171.73 (7)
O1^i—Mo1—O3	89.76 (6)	O1^viii—Zn2—O2^vii	96.01 (5)
O4—Mo1—O3	164.96 (9)	O1^ix—Zn2—O2^vii	96.01 (5)
O2—Mo1—O3	78.60 (6)	O2^x—Zn2—O2^vii	77.60 (7)
O2^ii—Mo1—O3	78.60 (6)	O2^xi—Zn2—O2^vii	77.60 (7)
O1—Mo1—Mo1^iii	49.63 (4)	Mo1—O1—Mo1^iii	80.75 (7)
O1^i—Mo1—Mo1^iii	95.26 (4)	Mo1—O1—Zn2	137.21 (4)
O4—Mo1—Mo1^iii	51.38 (4)	Mo1^iii—O1—Zn2	137.21 (4)
O2—Mo1—Mo1^iii	97.78 (4)	Zn1^xii—O2—Mo1	119.89 (5)
O2^ii—Mo1—Mo1^iii	141.34 (3)	Zn1^xii—O2—Mo1^xiii	119.89 (5)
O3—Mo1—Mo1^iii	139.34 (4)	Mo1—O2—Mo1^xiii	102.68 (7)
O1—Mo1—Mo1^i	95.26 (4)	Zn1^xii—O2—Zn2^xiv	111.56 (8)
O1^i—Mo1—Mo1^i	49.63 (4)	Mo1—O2—Zn2^xiv	99.62 (5)
O4—Mo1—Mo1^i	51.38 (4)	Mo1^xiii—O2—Zn2^xiv	99.62 (5)
O2—Mo1—Mo1^i	141.34 (3)	Zn1^xv—O3—Mo1^xiii	118.84 (7)
O2^ii—Mo1—Mo1^i	97.78 (4)	Zn1^xv—O3—Mo1^ii	118.84 (7)
O3—Mo1—Mo1^i	139.34 (4)	Mo1^xiii—O3—Mo1^ii	98.68 (9)
Mo1^iii—Mo1—Mo1^i	60.0	Zn1^xv—O3—Mo1	118.84 (7)
O3^iv—Zn1—O2^v	114.79 (5)	Mo1^xiii—O3—Mo1	98.68 (9)
O3^iv—Zn1—O2^vi	114.79 (5)	Mo1^ii—O3—Mo1	98.68 (9)
O2^v—Zn1—O2^vi	103.67 (6)	Mo1^iii—O4—Mo1	77.25 (8)
O3^iv—Zn1—O2^vii	114.79 (5)	Mo1^iii—O4—Mo1^i	77.25 (8)
O2^v—Zn1—O2^vii	103.67 (6)	Mo1—O4—Mo1^i	77.25 (8)
O2^vi—Zn1—O2^vii	103.67 (6)

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