Acta Cryst. (2008). E64, i66 [ doi:10.1107/S160053680802789X ]
Single crystals of the title compound, tetramagnesium diantimonate(V), were obtained by the slow cooling method with K2CO3. The structure is isotypic with ilmenite, which is constructed by the alternate stacking of layers consisting of metal-oxygen coordination octahedra. In each layer, the octahedra are connected by sharing edges so as to make holes. One of the two non-equivalent metal sites is fully occupied by Mg (3 symmetry), while the second metal site (3 symmetry) is disordered and occupied by Mg and Sb with occupation factors of 1/3 and 2/3, respectively.
Single crystals of the title compound were obtained unintentionally as the product of a synthesis of K-hollandite by the slow cooling method with excess K2CO3 (Michiue, 2007).
Partial substitution of Sb for Mg at the Mg2 site was checked by refining the occupation factors of Mg and Sb at the site. In the refinement the full occupation at all the metal and oxygen sites was assumed and the charge neutrality of the whole crystal was kept by imposing constraint conditions. The possibility of the existence of Sb ions at the Mg2 site was excluded because the occupation factor of Sb at the site was slightly negative, -0.001, and that of Mg was 1.001 after the refinement. Thus, it was concluded that Sb ions are only at the Mg1/Sb1 site.
Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994); cell refinement: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994); data reduction: Crystal Structure (Rigaku, 2004); program(s) used to solve structure: structure of the present compound is isotypic with ilmenite; program(s) used to refine structure: (JANA2000; Petříček et al., 2000); molecular graphics: ATOMS (Dowty, 2005); software used to prepare material for publication: (JANA2000; Petříček et al., 2000).
![[Figure 1]](./si2101fig1thm.gif)
| Fig. 1. The projection of Mg4Sb2O9 along [110]. |
![[Figure 2]](./si2101fig2thm.gif)
| Fig. 2. Layers with holes consisting of (a) Mg2O6 octahedra extending around z = 0 and (b) (Mg1/Sb1)O6 octahedra around z = 1/6 in Mg4Sb2O9. |
| Mg4O9Sb2 | Dx = 4.952 Mg m−3 |
| Mr = 484.7 | Mo Kα radiation, λ = 0.71069 Å |
| Trigonal, R3 | Cell parameters from 20 reflections |
| Hall symbol: -R 3 | θ = 9.3–13.5° |
| a = 5.1722 (11) Å | µ = 8.73 mm−1 |
| c = 14.028 (2) Å | T = 295 K |
| V = 324.99 (11) Å3 | Plate, colorless |
| Z = 2 | 0.22 × 0.22 × 0.04 mm |
| F(000) = 444 |
| Rigaku AFC-7R diffractometer | 715 reflections with I > 2σ(I) |
| Radiation source: rotating-anode X-ray tube | Rint = 0.047 |
| graphite | θmax = 50.1°, θmin = 4.4° |
| ω/2θ scans | h = −11→11 |
| Absorption correction: analytical (Tompa Analytical, Rigaku 2004) | k = −11→11 |
| Tmin = 0.210, Tmax = 0.671 | l = 0→30 |
| 2359 measured reflections | 3 standard reflections every 200 reflections |
| 773 independent reflections | intensity decay: 4.6% |
| Refinement on F2 | Primary atom site location: isomorphous structure methods |
| Least-squares matrix: full | Weighting scheme based on measured s.u.'s w = 1/(σ2(I) + 0.0009I2) |
| R[F2 > 2σ(F2)] = 0.032 | (Δ/σ)max = 0.0004 |
| wR(F2) = 0.075 | Δρmax = 3.78 e Å−3 |
| S = 1.55 | Δρmin = −3.64 e Å−3 |
| 773 reflections | Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974) |
| 17 parameters | Extinction coefficient: 0.071 (3) |
| 0 restraints |
| Mg4O9Sb2 | Z = 2 |
| Mr = 484.7 | Mo Kα radiation |
| Trigonal, R3 | µ = 8.73 mm−1 |
| a = 5.1722 (11) Å | T = 295 K |
| c = 14.028 (2) Å | 0.22 × 0.22 × 0.04 mm |
| V = 324.99 (11) Å3 |
| Rigaku AFC-7R diffractometer | 715 reflections with I > 2σ(I) |
| Absorption correction: analytical (Tompa Analytical, Rigaku 2004) | Rint = 0.047 |
| Tmin = 0.210, Tmax = 0.671 | θmax = 50.1° |
| 2359 measured reflections | 3 standard reflections every 200 reflections |
| 773 independent reflections | intensity decay: 4.6% |
| R[F2 > 2σ(F2)] = 0.032 | Δρmax = 3.78 e Å−3 |
| wR(F2) = 0.075 | Δρmin = −3.64 e Å−3 |
| S = 1.55 | Absolute structure: ? |
| 773 reflections | Flack parameter: ? |
| 17 parameters | Rogers parameter: ? |
| 0 restraints |
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| Mg1 | 0 | 0 | 0.152618 (14) | 0.00628 (7) | 0.3333 |
| M1 | 0 | 0 | 0.152618 (14) | 0.00628 (7) | 0.6667 |
| Mg2 | 0 | 0 | 0.35806 (10) | 0.0098 (2) | |
| O1 | 0.3091 (3) | 0.0125 (3) | 0.24710 (7) | 0.0078 (3) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Mg1 | 0.00711 (10) | 0.00711 (10) | 0.00461 (10) | 0.00356 (5) | 0 | 0 |
| M1 | 0.00711 (10) | 0.00711 (10) | 0.00461 (10) | 0.00356 (5) | 0 | 0 |
| Mg2 | 0.0080 (3) | 0.0080 (3) | 0.0133 (4) | 0.00401 (13) | 0 | 0 |
| O1 | 0.0097 (4) | 0.0073 (4) | 0.0069 (3) | 0.0047 (3) | −0.0010 (3) | 0.0011 (2) |
| M1—O1 | 2.0527 (15) | Mg2—O1 | 2.2091 (17) |
| M1—O1i | 1.9928 (11) | Mg2—O1vi | 2.0455 (17) |
| M1—O1ii | 2.0527 (19) | Mg2—O1ii | 2.209 (2) |
| M1—O1iii | 1.9928 (18) | Mg2—O1vii | 2.0455 (14) |
| M1—O1iv | 2.0527 (12) | Mg2—O1iv | 2.2091 (15) |
| M1—O1v | 1.9928 (17) | Mg2—O1viii | 2.046 (2) |
| O1—M1—O1i | 83.77 (5) | O1—Mg2—O1vi | 87.88 (6) |
| O1—M1—O1ii | 82.80 (6) | O1—Mg2—O1ii | 75.84 (7) |
| O1—M1—O1iii | 166.22 (6) | O1—Mg2—O1vii | 89.32 (5) |
| O1—M1—O1iv | 82.80 (6) | O1—Mg2—O1iv | 75.84 (7) |
| O1—M1—O1v | 92.43 (7) | O1—Mg2—O1viii | 160.12 (8) |
| O1i—M1—O1 | 83.77 (5) | O1vi—Mg2—O1 | 87.88 (6) |
| O1i—M1—O1ii | 92.43 (5) | O1vi—Mg2—O1ii | 160.12 (8) |
| O1i—M1—O1iii | 99.93 (6) | O1vi—Mg2—O1vii | 103.48 (8) |
| O1i—M1—O1iv | 166.22 (6) | O1vi—Mg2—O1iv | 89.32 (6) |
| O1i—M1—O1v | 99.93 (6) | O1vi—Mg2—O1viii | 103.48 (7) |
| O1ii—M1—O1 | 82.80 (6) | O1ii—Mg2—O1 | 75.84 (7) |
| O1ii—M1—O1i | 92.43 (5) | O1ii—Mg2—O1vi | 160.12 (8) |
| O1ii—M1—O1iii | 83.77 (7) | O1ii—Mg2—O1vii | 87.88 (6) |
| O1ii—M1—O1iv | 82.80 (6) | O1ii—Mg2—O1iv | 75.84 (7) |
| O1ii—M1—O1v | 166.22 (5) | O1ii—Mg2—O1viii | 89.32 (6) |
| O1iii—M1—O1 | 166.22 (6) | O1vii—Mg2—O1 | 89.32 (5) |
| O1iii—M1—O1i | 99.93 (6) | O1vii—Mg2—O1vi | 103.48 (8) |
| O1iii—M1—O1ii | 83.77 (7) | O1vii—Mg2—O1ii | 87.88 (6) |
| O1iii—M1—O1iv | 92.43 (7) | O1vii—Mg2—O1iv | 160.12 (8) |
| O1iii—M1—O1v | 99.93 (8) | O1vii—Mg2—O1viii | 103.48 (7) |
| O1iv—M1—O1 | 82.80 (6) | O1iv—Mg2—O1 | 75.84 (7) |
| O1iv—M1—O1i | 166.22 (6) | O1iv—Mg2—O1vi | 89.32 (6) |
| O1iv—M1—O1ii | 82.80 (6) | O1iv—Mg2—O1ii | 75.84 (7) |
| O1iv—M1—O1iii | 92.43 (7) | O1iv—Mg2—O1vii | 160.12 (8) |
| O1iv—M1—O1v | 83.77 (6) | O1iv—Mg2—O1viii | 87.88 (6) |
| O1v—M1—O1 | 92.43 (7) | O1viii—Mg2—O1 | 160.12 (8) |
| O1v—M1—O1i | 99.93 (6) | O1viii—Mg2—O1vi | 103.48 (7) |
| O1v—M1—O1ii | 166.22 (5) | O1viii—Mg2—O1ii | 89.32 (6) |
| O1v—M1—O1iii | 99.93 (8) | O1viii—Mg2—O1vii | 103.48 (7) |
| O1v—M1—O1iv | 83.77 (6) | O1viii—Mg2—O1iv | 87.88 (6) |
| Symmetry codes: (i) −x+2/3, −y+1/3, −z+1/3; (ii) −y, x−y, z; (iii) y−1/3, −x+y+1/3, −z+1/3; (iv) −x+y, −x, z; (v) x−y−1/3, x−2/3, −z+1/3; (vi) −x+1/3, −y−1/3, −z+2/3; (vii) y+1/3, −x+y+2/3, −z+2/3; (viii) x−y−2/3, x−1/3, −z+2/3. |
| M1—O1 | 2.0527 (15) | Mg2—O1 | 2.2091 (17) |
| M1—O1i | 1.9928 (11) | Mg2—O1vi | 2.0455 (17) |
| M1—O1ii | 2.0527 (19) | Mg2—O1ii | 2.209 (2) |
| M1—O1iii | 1.9928 (18) | Mg2—O1vii | 2.0455 (14) |
| M1—O1iv | 2.0527 (12) | Mg2—O1iv | 2.2091 (15) |
| M1—O1v | 1.9928 (17) | Mg2—O1viii | 2.046 (2) |
| Symmetry codes: (i) −x+2/3, −y+1/3, −z+1/3; (ii) −y, x−y, z; (iii) y−1/3, −x+y+1/3, −z+1/3; (iv) −x+y, −x, z; (v) x−y−1/3, x−2/3, −z+1/3; (vi) −x+1/3, −y−1/3, −z+2/3; (vii) y+1/3, −x+y+2/3, −z+2/3; (viii) x−y−2/3, x−1/3, −z+2/3. |
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A pronounced resemblance of X-ray diffraction patterns for Mg4Sb2O9 and the ilmenite MgTiO3 was pointed out by Blasse (1964). In general, ilmenite structure is represented by A2+B4+O3, that is including equal amounts of divalent and tetravalent cations such as FeTiO3 and MgTiO3. Although the chemical composition Mg4Sb2O9 is away from that of the typical ilmenite structure, the present analysis has confirmed that the structure of Mg4Sb2O9 is deduced from the ilmenite MgTiO3 by replacing the Ti4+ ions statistically by 1/3 Mg2+ and 2/3 Sb5+, as was supposed by Blasse (1964).
The structure is constructed by the alternate stacking of atomic layers along c as shown in Fig. 1. Each of the two nonequivalent metal sites is octahedrally coordinated by six oxygen ions. Two types of layers consisting of edge-shared octahedra are seen in the structure, both of which have holes as illustrated in Fig. 2.