Mg₄Sb₂O₉ of the ilmenite structure type

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.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](Mg-O) = 0.002 Å
• Disorder in main residue
• R factor = 0.032
• wR factor = 0.075
• Data-to-parameter ratio = 45.5

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT301_ALERT_3_C Main Residue  Disorder .........................      18.00 Perc.
PLAT076_ALERT_1_C Occupancy       0.33 less than 1.0 for Sp.pos  .        MG1

Alert level G
ABSTM02_ALERT_3_G  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.210     0.671
            Tmin and Tmax expected:      0.166     0.705
            RR =      1.326
            Please check that your absorption correction is appropriate.

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

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.

Related literature

For ilmenite structures, see: Wechsler et al. (1984) for FeTiO₃ and Wechsler et al. (1989) for MgTiO₃. For further phases in the MgO–Sb₂O₅ system, see: Kasper (1969).

For related literature, see: Becker & Coppens (1974); Blasse (1964); Michiue (2007); Rigaku (2004).

S2. Experimental

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).

S3. Refinement

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.

Computing details

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).

Figures

	Fig. 1. The projection of Mg4Sb2O9 along [110].
	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.

tetramagnesium diantimonate

Crystal data

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) Å^3	Plate, colorless
Z = 2	0.22 × 0.22 × 0.04 mm
F(000) = 444

Data collection

Rigaku AFC-7R diffractometer	715 reflections with I > 2σ(I)
Radiation source: rotating-anode X-ray tube	Rint = 0.047
Graphite monochromator	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

Refinement on F^2	Primary atom site location: isomorphous structure methods
Least-squares matrix: full	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0009I^2)
R[F^2 > 2σ(F^2)] = 0.032	(Δ/σ)max = 0.0004
wR(F^2) = 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

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

	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)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

M1—O1	2.0527 (15)	Mg2—O1	2.2091 (17)
M1—O1^i	1.9928 (11)	Mg2—O1^vi	2.0455 (17)
M1—O1^ii	2.0527 (19)	Mg2—O1^ii	2.209 (2)
M1—O1^iii	1.9928 (18)	Mg2—O1^vii	2.0455 (14)
M1—O1^iv	2.0527 (12)	Mg2—O1^iv	2.2091 (15)
M1—O1^v	1.9928 (17)	Mg2—O1^viii	2.046 (2)
O1—M1—O1^i	83.77 (5)	O1—Mg2—O1^vi	87.88 (6)
O1—M1—O1^ii	82.80 (6)	O1—Mg2—O1^ii	75.84 (7)
O1—M1—O1^iii	166.22 (6)	O1—Mg2—O1^vii	89.32 (5)
O1—M1—O1^iv	82.80 (6)	O1—Mg2—O1^iv	75.84 (7)
O1—M1—O1^v	92.43 (7)	O1—Mg2—O1^viii	160.12 (8)
O1^i—M1—O1	83.77 (5)	O1^vi—Mg2—O1	87.88 (6)
O1^i—M1—O1^ii	92.43 (5)	O1^vi—Mg2—O1^ii	160.12 (8)
O1^i—M1—O1^iii	99.93 (6)	O1^vi—Mg2—O1^vii	103.48 (8)
O1^i—M1—O1^iv	166.22 (6)	O1^vi—Mg2—O1^iv	89.32 (6)
O1^i—M1—O1^v	99.93 (6)	O1^vi—Mg2—O1^viii	103.48 (7)
O1^ii—M1—O1	82.80 (6)	O1^ii—Mg2—O1	75.84 (7)
O1^ii—M1—O1^i	92.43 (5)	O1^ii—Mg2—O1^vi	160.12 (8)
O1^ii—M1—O1^iii	83.77 (7)	O1^ii—Mg2—O1^vii	87.88 (6)
O1^ii—M1—O1^iv	82.80 (6)	O1^ii—Mg2—O1^iv	75.84 (7)
O1^ii—M1—O1^v	166.22 (5)	O1^ii—Mg2—O1^viii	89.32 (6)
O1^iii—M1—O1	166.22 (6)	O1^vii—Mg2—O1	89.32 (5)
O1^iii—M1—O1^i	99.93 (6)	O1^vii—Mg2—O1^vi	103.48 (8)
O1^iii—M1—O1^ii	83.77 (7)	O1^vii—Mg2—O1^ii	87.88 (6)
O1^iii—M1—O1^iv	92.43 (7)	O1^vii—Mg2—O1^iv	160.12 (8)
O1^iii—M1—O1^v	99.93 (8)	O1^vii—Mg2—O1^viii	103.48 (7)
O1^iv—M1—O1	82.80 (6)	O1^iv—Mg2—O1	75.84 (7)
O1^iv—M1—O1^i	166.22 (6)	O1^iv—Mg2—O1^vi	89.32 (6)
O1^iv—M1—O1^ii	82.80 (6)	O1^iv—Mg2—O1^ii	75.84 (7)
O1^iv—M1—O1^iii	92.43 (7)	O1^iv—Mg2—O1^vii	160.12 (8)
O1^iv—M1—O1^v	83.77 (6)	O1^iv—Mg2—O1^viii	87.88 (6)
O1^v—M1—O1	92.43 (7)	O1^viii—Mg2—O1	160.12 (8)
O1^v—M1—O1^i	99.93 (6)	O1^viii—Mg2—O1^vi	103.48 (7)
O1^v—M1—O1^ii	166.22 (5)	O1^viii—Mg2—O1^ii	89.32 (6)
O1^v—M1—O1^iii	99.93 (8)	O1^viii—Mg2—O1^vii	103.48 (7)
O1^v—M1—O1^iv	83.77 (6)	O1^viii—Mg2—O1^iv	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.