Acta Cryst. (2009). E65, i51 [ doi:10.1107/S1600536809021928 ]
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.
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.
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).
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).
![[Figure 1]](./wm2235fig1thm.gif)
| Fig. 1. : View of Zn2Mo3O8 along [110]. |
![[Figure 2]](./wm2235fig2thm.gif)
| Fig. 2. : Plot showing the atom-numbering scheme of the Mo3O13 cluster unit. Displacement ellipsoids are drawn at the 97% probability level. |
| 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) Å3 | Irregular block, black |
| Z = 2 | 0.21 × 0.13 × 0.07 mm |
| F(000) = 500 |
| Nonius KappaCCD diffractometer | 790 independent reflections |
| Radiation source: fine-focus sealed tube | 778 reflections with I > 2σ(I) |
| graphite | 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 on F2 | Secondary atom site location: difference Fourier map |
| Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0117P)2 + 0.2665P] where P = (Fo2 + 2Fc2)/3 |
| R[F2 > 2σ(F2)] = 0.013 | (Δ/σ)max = 0.001 |
| wR(F2) = 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+0.001xFc2λ3/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 | Flack parameter: 0.155 (15) |
| Zn2Mo3O8 | Z = 2 |
| Mr = 546.56 | Mo Kα radiation |
| Hexagonal, P63mc | µ = 14.59 mm−1 |
| a = 5.7816 (2) Å | T = 293 K |
| c = 9.9345 (3) Å | 0.21 × 0.13 × 0.07 mm |
| V = 287.59 (2) Å3 |
| Nonius KappaCCD diffractometer | 790 independent reflections |
| Absorption correction: analytical (de Meulenaer & Tompa, 1965) | 778 reflections with I > 2σ(I) |
| Tmin = 0.048, Tmax = 0.157 | Rint = 0.023 |
| 8536 measured reflections | θmax = 44.0° |
| R[F2 > 2σ(F2)] = 0.013 | 1 restraint |
| wR(F2) = 0.029 | Δρmax = 0.97 e Å−3 |
| S = 1.16 | Δρmin = −1.06 e Å−3 |
| 790 reflections | Absolute structure: Flack (1983), 322 Friedel pairs |
| 33 parameters | Flack parameter: 0.155 (15) |
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. |
| 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) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| 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 |
| Mo1—O1 | 1.9549 (14) | Zn1—O2v | 1.9687 (15) |
| Mo1—O1i | 1.9549 (14) | Zn1—O2vi | 1.9687 (15) |
| Mo1—O4 | 2.0286 (19) | Zn1—O2vii | 1.9687 (15) |
| Mo1—O2 | 2.0804 (10) | Zn2—O1 | 2.0467 (18) |
| Mo1—O2ii | 2.0804 (10) | Zn2—O1viii | 2.0467 (18) |
| Mo1—O3 | 2.1415 (14) | Zn2—O1ix | 2.0467 (18) |
| Mo1—Mo1iii | 2.5326 (2) | Zn2—O2x | 2.1431 (16) |
| Mo1—Mo1i | 2.5326 (2) | Zn2—O2xi | 2.1431 (16) |
| Zn1—O3iv | 1.963 (3) | Zn2—O2vii | 2.1431 (16) |
| O1—Mo1—O1i | 95.38 (11) | O1—Zn2—O1viii | 89.84 (8) |
| O1—Mo1—O4 | 100.30 (5) | O1—Zn2—O1ix | 89.84 (8) |
| O1i—Mo1—O4 | 100.30 (5) | O1viii—Zn2—O1ix | 89.84 (8) |
| O1—Mo1—O2 | 91.06 (7) | O1—Zn2—O2x | 96.01 (5) |
| O1i—Mo1—O2 | 166.69 (5) | O1viii—Zn2—O2x | 171.73 (8) |
| O4—Mo1—O2 | 89.96 (6) | O1ix—Zn2—O2x | 96.01 (5) |
| O1—Mo1—O2ii | 166.69 (5) | O1—Zn2—O2xi | 96.01 (5) |
| O1i—Mo1—O2ii | 91.06 (7) | O1viii—Zn2—O2xi | 96.01 (5) |
| O4—Mo1—O2ii | 89.96 (6) | O1ix—Zn2—O2xi | 171.73 (7) |
| O2—Mo1—O2ii | 80.41 (8) | O2x—Zn2—O2xi | 77.60 (7) |
| O1—Mo1—O3 | 89.76 (6) | O1—Zn2—O2vii | 171.73 (7) |
| O1i—Mo1—O3 | 89.76 (6) | O1viii—Zn2—O2vii | 96.01 (5) |
| O4—Mo1—O3 | 164.96 (9) | O1ix—Zn2—O2vii | 96.01 (5) |
| O2—Mo1—O3 | 78.60 (6) | O2x—Zn2—O2vii | 77.60 (7) |
| O2ii—Mo1—O3 | 78.60 (6) | O2xi—Zn2—O2vii | 77.60 (7) |
| O1—Mo1—Mo1iii | 49.63 (4) | Mo1—O1—Mo1iii | 80.75 (7) |
| O1i—Mo1—Mo1iii | 95.26 (4) | Mo1—O1—Zn2 | 137.21 (4) |
| O4—Mo1—Mo1iii | 51.38 (4) | Mo1iii—O1—Zn2 | 137.21 (4) |
| O2—Mo1—Mo1iii | 97.78 (4) | Zn1xii—O2—Mo1 | 119.89 (5) |
| O2ii—Mo1—Mo1iii | 141.34 (3) | Zn1xii—O2—Mo1xiii | 119.89 (5) |
| O3—Mo1—Mo1iii | 139.34 (4) | Mo1—O2—Mo1xiii | 102.68 (7) |
| O1—Mo1—Mo1i | 95.26 (4) | Zn1xii—O2—Zn2xiv | 111.56 (8) |
| O1i—Mo1—Mo1i | 49.63 (4) | Mo1—O2—Zn2xiv | 99.62 (5) |
| O4—Mo1—Mo1i | 51.38 (4) | Mo1xiii—O2—Zn2xiv | 99.62 (5) |
| O2—Mo1—Mo1i | 141.34 (3) | Zn1xv—O3—Mo1xiii | 118.84 (7) |
| O2ii—Mo1—Mo1i | 97.78 (4) | Zn1xv—O3—Mo1ii | 118.84 (7) |
| O3—Mo1—Mo1i | 139.34 (4) | Mo1xiii—O3—Mo1ii | 98.68 (9) |
| Mo1iii—Mo1—Mo1i | 60.0 | Zn1xv—O3—Mo1 | 118.84 (7) |
| O3iv—Zn1—O2v | 114.79 (5) | Mo1xiii—O3—Mo1 | 98.68 (9) |
| O3iv—Zn1—O2vi | 114.79 (5) | Mo1ii—O3—Mo1 | 98.68 (9) |
| O2v—Zn1—O2vi | 103.67 (6) | Mo1iii—O4—Mo1 | 77.25 (8) |
| O3iv—Zn1—O2vii | 114.79 (5) | Mo1iii—O4—Mo1i | 77.25 (8) |
| O2v—Zn1—O2vii | 103.67 (6) | Mo1—O4—Mo1i | 77.25 (8) |
| O2vi—Zn1—O2vii | 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. |
| Mo1—O1 | 1.9549 (14) | Mo1—Mo1i | 2.5326 (2) |
| Mo1—O4 | 2.0286 (19) | Zn1—O3ii | 1.963 (3) |
| Mo1—O2 | 2.0804 (10) | Zn2—O1 | 2.0467 (18) |
| Mo1—O3 | 2.1415 (14) | Zn2—O2iii | 2.1431 (16) |
| Symmetry codes: (i) −x+y, −x, z; (ii) x, y+1, z; (iii) y, −x+y, z+1/2. |
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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 Mo3O4O6/2O3/3. 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).