The iron molybdate NaMgFe(MoO4)3 is isostructural with α-NaFe2(MoO4)3 and its structure is built up from [Mg,Fe]2O10 units of edge-sharing [Mg,Fe]O6 octahedra which are linked to each other through the common corners of [MoO4] tetrahedra. The resulting anionic three-dimensional framework leads to the formation of channels along the [101] direction, where the Na+ cations are located.
Keywords: crystal structure, iron molybdate, anionic framework, Na–Fe–Mo–O system
Abstract
The iron molybdate NaMgFe(MoO4)3 {sodium magnesium iron(III) tris[molybdate(VI)]} has been synthesized by the flux method. This compound is isostructural with α-NaFe2(MoO4)3 and crystallizes in the triclinic space group P-1. Its structure is built up from [Mg,Fe]2O10 units of edge-sharing [Mg,Fe]O6 octahedra which are linked to each other through the common corners of [MoO4] tetrahedra. The resulting anionic three-dimensional framework leads to the formation of channels along the [101] direction in which the Na+ cations are located.
Chemical context
Iron molybdates have been subject to very intensive research as a result of their numerous applications including as catalysts (Tian et al., 2011 ▸), multiferroic properties and more recently as a possible positive electrode in rechargeable batteries (Sinyakov et al., 1978 ▸; Mączka et al., 2011 ▸; Devi & Varadaraju, 2012 ▸). In these materials, the anionic framework is constructed from MoO4 tetrahedra linked to the iron coordination polyhedra, leading to a large variety of crystal structures with a high capacity for cationic and anionic substitutions.
Until now, a total of six orthomolybdate compounds have been reported in the Na–Fe–Mo–O system: Na9Fe(MoO4)6 (Savina et al., 2013 ▸); NaFe(MoO4)2 (Klevtsova, 1975 ▸); α-NaFe2(MoO4)3, β-NaFe2(MoO4)3 and Na3Fe2(MoO4)3 (Muessig et al., 2003 ▸); NaFe4(MoO4)5 (Ehrenberg et al., 2006 ▸). Their structures are described in terms of three-dimensional networks of isolated [MoO4] tetrahedra and [FeO6] octahedra. The sodium and mixed-valence iron molybdate NaFe2(MoO4)3 exhibits two polymorphs, both crystallizing in the triclinic system. The low-temperature α-phase changes irreversibly at high temperature into a β-phase. In addition to these orthomolybdate compounds, another phase with the formula Na3Fe2Mo5O16 and with layers of Mo3O13 units consisting of [MoO6] octahedra has been synthesized and characterized (Bramnik et al., 2003 ▸). In addition, Kozhevnikova & Imekhenova (2009 ▸) have investigated the Na2MoO4–MMoO4–Fe2(MoO4)3 system (M = Mg, Mn, Ni, Co) and have attributed the Nasicon-type structure with space group R
c (Kotova & Kozhevnikova, 2003 ▸; Kozhevnikova & Imekhenova, 2009 ▸) to the phase of variable composition Na(1−x)
M
(1−x)Fe(1+x)(MoO4)3. More recently, NaNiFe(MoO4)3 and NaZnFe(MoO4)3 (Mhiri et al., 2015 ▸) were found to be isostructural to β-NaFe2(MoO4)3 and to have a good ionic conductivity with low activation energy, close to those of Nasicon-type compounds with similar formula such as AZr2(PO4)3 (A = Na, Li). As an extension of the previous work, we report here on the synthesis and characterization by X-ray diffraction of a new compound, NaMgFe(MoO4)3, which is isostructural with α-NaFe2(MoO4)3.
Structural commentary
The title NaMgFe(MoO4)3 structure is based on a three-dimensional framework of [Mg,Fe]2O10 units of edge-sharing [Mg,Fe]O6 octahedra, connected to each other through the common corners of [MoO4] tetrahedra. All [Mg,Fe]2O10 units are parallel to [1
0] (Fig. 1 ▸). In this structure, two types of layers (A and B), similar to those observed in α-NaFe2(MoO4)3, are aligned parallel to (110) with the sequence –A–B–B′–A–B–B′– and stacked along [001]. B′ layers are obtained from B by an inversion centre located on the A planes (Fig. 2 ▸). The resulting anionic three-dimensional framework leads to the formation of channels along [101] in which the sodium ions are located (Fig. 3 ▸).
Figure 1.
[Mg,Fe]2O10 units parallel to [10] in NaMgFe(MoO4)3 structure. [Mg,Fe]2O10 dimers are shown in blue and MoO4 tetrahedra in purple.
Figure 2.
Projection of the NaMgFe(MoO4)3 structure along the b axis. [Mg,Fe]2O10 dimers are shown in blue; MoO4 tetrahedra in purple and Na+ cations as green spheres.
Figure 3.
Channels along [101] in the structure of NaMgFe(MoO4)3. [Mg,Fe]2O10 dimers are shown in blue, MoO4 tetrahedra in purple and Na+ cations as green spheres.
In the title structure, all atoms are located in general positions. The three crystallographically different molybdenum atoms have a tetrahedral coordination with Mo—O distances between 1.715 (3) and 1.801 (2) Å. The mean distances (Mo1—O = 1.762, Mo2—O = 1.766 and Mo3—O = 1.760 Å) are in good accordance with those usually observed in molybdates (Abrahams et al., 1967 ▸; Harrison & Cheetham, 1989 ▸; Smit et al., 2006 ▸). The [Mg,Fe]—O distances and the cis O—[Mg,Fe]—O angles in the [Mg,Fe]2O10 units range from 2.003 (3) to 2.099 (3) Å and from 81.2 (1) to 177.8 (1)°, respectively. This dispersion reflects a slight distortion of the [Mg,Fe]O6 octahedra. The average distances [Mg,Fe]1—O = 2.059 and [Mg,Fe]2—O = 2.013 Å lie between the values of 1.990 Å observed for six-coordinated Fe3+ in LiFe(MoO4)2 (van der Lee et al. 2008 ▸) and 2.072 Å reported for Mg2+ with the same coordination in NaMg3Al(MoO4)5 (Hermanowicz et al., 2006 ▸). This result is related to the disordered distribution of Fe3+ and Mg2+ in both sites. Assuming sodium–oxygen distances below 3.13 Å (Donnay & Allmann, 1970 ▸), the Na site is surrounded by five oxygen atoms (Fig. 4 ▸).
Figure 4.
The environment of the Na+ cation showing displacement ellipsoids drawn at the 50% probability level.
Synthesis and crystallization
Crystals of the title compound were grown in a flux of sodium dimolybdate Na2Mo2O7 with an atomic ratio Na:Mg:Fe:Mo = 5:1:1:7. Appropriate amounts of the starting reactants NaNO3, Mg(NO3)2·6H2O, Fe(NO3)3·9H2O and (NH4)6Mo7O24·4H2O were dissolved in nitric acid and the resulting solution was evaporated to dryness. The dry residue was then placed in a platinum crucible and slowly heated in air up to 673 K for 24 h to remove H2O and NH3. The mixture was ground in an agate mortar, melted for 2 h at 1123 K and then cooled to room temperature at a rate of 5 K h−1. Crystals without regular shape were separated from the flux by washing in boiling water.
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. The application of the direct methods revealed two sites, labeled M(1) and M(2), statistically occupied by the Fe3+ and Mg2+ ions. This distribution was supported by the M1—O and M2—O distances which are between the classical values for pure Mg—O and Fe—O bonds. Succeeding difference Fourier synthesis led to the positions of all the remaining atoms.
Table 1. Experimental details.
| Crystal data | |
| Chemical formula | NaMgFe(MoO4)3 |
| M r | 582.97 |
| Crystal system, space group | Triclinic, P
|
| Temperature (K) | 293 |
| a, b, c (Å) | 6.900 (4), 6.928 (1), 11.055 (1) |
| α, β, γ (°) | 80.24 (1), 83.55 (2), 80.22 (3) |
| V (Å3) | 511.3 (3) |
| Z | 2 |
| Radiation type | Mo Kα |
| μ (mm−1) | 5.15 |
| Crystal size (mm) | 0.28 × 0.14 × 0.07 |
| Data collection | |
| Diffractometer | Enraf–Nonius TurboCAD-4 |
| Absorption correction | ψ scan (North et al., 1968 ▸) |
| T min, T max | 0.478, 0.695 |
| No. of measured, independent and observed [I > 2σ(I)] reflections | 3429, 2983, 2850 |
| R int | 0.014 |
| (sin θ/λ)max (Å−1) | 0.703 |
| Refinement | |
| R[F 2 > 2σ(F 2)], wR(F 2), S | 0.025, 0.068, 1.19 |
| No. of reflections | 2983 |
| No. of parameters | 168 |
| No. of restraints | 4 |
| Δρmax, Δρmin (e Å−3) | 1.47, −1.60 |
Supplementary Material
Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S205698901600829X/br2259sup1.cif
Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901600829X/br2259Isup2.hkl
CCDC reference: 1481125
Additional supporting information: crystallographic information; 3D view; checkCIF report
supplementary crystallographic information
Crystal data
| FeMgMo3NaO12 | Z = 2 |
| Mr = 582.97 | F(000) = 542 |
| Triclinic, P1 | Dx = 3.786 Mg m−3 |
| a = 6.900 (4) Å | Mo Kα radiation, λ = 0.71073 Å |
| b = 6.928 (1) Å | Cell parameters from 25 reflections |
| c = 11.055 (1) Å | θ = 9.1–11.4° |
| α = 80.24 (1)° | µ = 5.15 mm−1 |
| β = 83.55 (2)° | T = 293 K |
| γ = 80.22 (3)° | Prism, brown |
| V = 511.3 (3) Å3 | 0.28 × 0.14 × 0.07 mm |
Data collection
| Enraf–Nonius TurboCAD-4 diffractometer | Rint = 0.014 |
| Radiation source: fine-focus sealed tube | θmax = 30.0°, θmin = 3.0° |
| non–profiled ω/2τ scans | h = −9→9 |
| Absorption correction: ψ scan (North et al., 1968) | k = −9→9 |
| Tmin = 0.478, Tmax = 0.695 | l = −1→15 |
| 3429 measured reflections | 2 standard reflections every 120 min |
| 2983 independent reflections | intensity decay: 1.1% |
| 2850 reflections with I > 2σ(I) |
Refinement
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.025 | w = 1/[σ2(Fo2) + (0.0308P)2 + 2.3858P] where P = (Fo2 + 2Fc2)/3 |
| wR(F2) = 0.068 | (Δ/σ)max = 0.001 |
| S = 1.19 | Δρmax = 1.47 e Å−3 |
| 2983 reflections | Δρmin = −1.60 e Å−3 |
| 168 parameters | Extinction correction: SHELXL2014/7 (Sheldrick 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 4 restraints | Extinction coefficient: 0.0074 (5) |
Special details
| Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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 (Å2)
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| Na | 0.8586 (4) | 0.5914 (4) | 0.8148 (4) | 0.0757 (12) | |
| Mg1 | 0.8152 (1) | 0.1703 (1) | 0.50854 (8) | 0.00851 (16) | 0.7558 (7) |
| Fe1 | 0.8152 (1) | 0.1703 (1) | 0.50854 (8) | 0.00851 (16) | 0.2442 (7) |
| Mg2 | 0.77528 (8) | 0.77491 (8) | 0.11025 (5) | 0.00785 (12) | 0.2442 (7) |
| Fe2 | 0.77528 (8) | 0.77491 (8) | 0.11025 (5) | 0.00785 (12) | 0.7558 (7) |
| Mo1 | 0.75910 (4) | 0.10066 (4) | 0.85110 (2) | 0.00799 (8) | |
| O11 | 0.8166 (4) | 0.8508 (4) | 0.9264 (2) | 0.0125 (5) | |
| O12 | 0.9297 (4) | 0.2547 (4) | 0.8737 (3) | 0.0146 (5) | |
| O13 | 0.5170 (4) | 0.2053 (4) | 0.8938 (3) | 0.0158 (5) | |
| O14 | 0.7784 (5) | 0.0889 (4) | 0.6953 (2) | 0.0185 (5) | |
| Mo2 | 0.70522 (4) | 0.28318 (4) | 0.18835 (3) | 0.00950 (8) | |
| O21 | 0.4579 (4) | 0.3458 (5) | 0.2289 (3) | 0.0232 (6) | |
| O22 | 0.7436 (4) | 0.0675 (4) | 0.1148 (3) | 0.0185 (5) | |
| O23 | 0.8372 (4) | 0.2322 (4) | 0.3205 (2) | 0.0173 (5) | |
| O24 | 0.8015 (4) | 0.4878 (4) | 0.0918 (2) | 0.0148 (5) | |
| Mo3 | 0.27372 (4) | 0.29658 (4) | 0.54507 (2) | 0.00732 (8) | |
| O31 | 0.1224 (4) | 0.1328 (4) | 0.5056 (2) | 0.0113 (4) | |
| O32 | 0.2458 (5) | 0.2976 (4) | 0.7045 (2) | 0.0194 (5) | |
| O33 | 0.5183 (4) | 0.2083 (4) | 0.5042 (3) | 0.0172 (5) | |
| O34 | 0.2067 (4) | 0.5383 (4) | 0.4690 (3) | 0.0153 (5) |
Atomic displacement parameters (Å2)
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Na | 0.0293 (12) | 0.0255 (11) | 0.186 (4) | 0.0089 (9) | −0.0496 (18) | −0.0429 (17) |
| Mg1 | 0.0079 (4) | 0.0081 (4) | 0.0091 (4) | −0.0007 (3) | −0.0018 (3) | 0.0001 (3) |
| Fe1 | 0.0079 (4) | 0.0081 (4) | 0.0091 (4) | −0.0007 (3) | −0.0018 (3) | 0.0001 (3) |
| Mg2 | 0.0080 (2) | 0.0073 (2) | 0.0079 (2) | −0.00174 (18) | −0.00177 (18) | 0.00103 (18) |
| Fe2 | 0.0080 (2) | 0.0073 (2) | 0.0079 (2) | −0.00174 (18) | −0.00177 (18) | 0.00103 (18) |
| Mo1 | 0.00697 (13) | 0.00870 (13) | 0.00770 (13) | −0.00175 (9) | −0.00095 (9) | 0.00122 (9) |
| O11 | 0.0163 (12) | 0.0106 (11) | 0.0094 (11) | −0.0013 (9) | −0.0021 (9) | 0.0019 (8) |
| O12 | 0.0112 (11) | 0.0152 (12) | 0.0182 (12) | −0.0052 (9) | −0.0040 (9) | 0.0003 (10) |
| O13 | 0.0090 (11) | 0.0178 (12) | 0.0194 (13) | −0.0009 (9) | −0.0016 (9) | −0.0005 (10) |
| O14 | 0.0258 (14) | 0.0185 (13) | 0.0092 (11) | −0.0021 (11) | −0.0017 (10) | 0.0018 (10) |
| Mo2 | 0.01041 (14) | 0.00802 (13) | 0.00985 (13) | −0.00235 (9) | −0.00173 (9) | 0.00076 (9) |
| O21 | 0.0133 (12) | 0.0295 (16) | 0.0261 (15) | −0.0028 (11) | −0.0017 (11) | −0.0026 (12) |
| O22 | 0.0226 (14) | 0.0110 (12) | 0.0229 (14) | −0.0050 (10) | −0.0032 (11) | −0.0017 (10) |
| O23 | 0.0192 (13) | 0.0188 (13) | 0.0125 (12) | −0.0009 (10) | −0.0033 (10) | 0.0005 (10) |
| O24 | 0.0203 (13) | 0.0100 (11) | 0.0129 (11) | −0.0016 (9) | 0.0019 (9) | −0.0012 (9) |
| Mo3 | 0.00771 (13) | 0.00787 (13) | 0.00674 (13) | −0.00290 (9) | −0.00105 (9) | −0.00015 (9) |
| O31 | 0.0093 (10) | 0.0089 (10) | 0.0167 (12) | −0.0027 (8) | −0.0026 (9) | −0.0027 (9) |
| O32 | 0.0266 (15) | 0.0239 (14) | 0.0088 (11) | −0.0081 (11) | −0.0019 (10) | −0.0010 (10) |
| O33 | 0.0107 (11) | 0.0198 (13) | 0.0212 (13) | −0.0025 (10) | −0.0018 (10) | −0.0025 (10) |
| O34 | 0.0189 (13) | 0.0086 (11) | 0.0179 (12) | −0.0027 (9) | −0.0027 (10) | 0.0008 (9) |
Geometric parameters (Å, º)
| Na—O21i | 2.244 (4) | Mg2—O32i | 2.019 (3) |
| Na—O12 | 2.296 (4) | Mg2—O12ii | 2.036 (3) |
| Na—O11 | 2.308 (4) | Mo1—O14 | 1.727 (3) |
| Na—O24ii | 2.604 (4) | Mo1—O13 | 1.751 (3) |
| Na—O23ii | 2.772 (5) | Mo1—O12 | 1.780 (3) |
| Mg1—O33 | 2.025 (3) | Mo1—O11vii | 1.789 (3) |
| Mg1—O23 | 2.044 (3) | Mo2—O21 | 1.715 (3) |
| Mg1—O14 | 2.045 (3) | Mo2—O23 | 1.761 (3) |
| Mg1—O34i | 2.054 (3) | Mo2—O22 | 1.787 (3) |
| Mg1—O31iii | 2.089 (3) | Mo2—O24 | 1.799 (3) |
| Mg1—O31iv | 2.099 (3) | Mo3—O33 | 1.731 (3) |
| Mg2—O13i | 2.003 (3) | Mo3—O32 | 1.753 (3) |
| Mg2—O24 | 2.009 (3) | Mo3—O34 | 1.753 (3) |
| Mg2—O22v | 2.010 (3) | Mo3—O31 | 1.801 (2) |
| Mg2—O11vi | 2.012 (3) | ||
| O21i—Na—O12 | 106.29 (15) | O24—Mg2—O11vi | 90.58 (11) |
| O21i—Na—O11 | 92.34 (14) | O22v—Mg2—O11vi | 85.22 (11) |
| O12—Na—O11 | 131.5 (2) | O13i—Mg2—O32i | 91.56 (12) |
| O21i—Na—O24ii | 169.3 (2) | O24—Mg2—O32i | 90.53 (12) |
| O12—Na—O24ii | 71.63 (12) | O22v—Mg2—O32i | 93.77 (12) |
| O11—Na—O24ii | 81.96 (12) | O11vi—Mg2—O32i | 175.79 (12) |
| O21i—Na—O23ii | 125.19 (19) | O13i—Mg2—O12ii | 176.14 (11) |
| O12—Na—O23ii | 115.39 (14) | O24—Mg2—O12ii | 90.70 (12) |
| O11—Na—O23ii | 85.84 (12) | O22v—Mg2—O12ii | 91.08 (12) |
| O24ii—Na—O23ii | 63.66 (10) | O11vi—Mg2—O12ii | 91.24 (11) |
| O33—Mg1—O23 | 88.07 (12) | O32i—Mg2—O12ii | 84.69 (12) |
| O33—Mg1—O14 | 88.89 (12) | O14—Mo1—O13 | 108.16 (14) |
| O23—Mg1—O14 | 174.80 (12) | O14—Mo1—O12 | 106.87 (14) |
| O33—Mg1—O34i | 89.20 (12) | O13—Mo1—O12 | 110.69 (13) |
| O23—Mg1—O34i | 93.92 (12) | O14—Mo1—O11vii | 106.05 (13) |
| O14—Mg1—O34i | 90.26 (12) | O13—Mo1—O11vii | 111.66 (13) |
| O33—Mg1—O31iii | 177.80 (12) | O12—Mo1—O11vii | 113.08 (12) |
| O23—Mg1—O31iii | 89.73 (11) | O21—Mo2—O23 | 110.07 (14) |
| O14—Mg1—O31iii | 93.30 (12) | O21—Mo2—O22 | 109.36 (15) |
| O34i—Mg1—O31iii | 91.09 (11) | O23—Mo2—O22 | 109.03 (13) |
| O33—Mg1—O31iv | 98.59 (12) | O21—Mo2—O24 | 110.70 (14) |
| O23—Mg1—O31iv | 88.75 (11) | O23—Mo2—O24 | 105.75 (13) |
| O14—Mg1—O31iv | 87.53 (11) | O22—Mo2—O24 | 111.86 (13) |
| O34i—Mg1—O31iv | 171.86 (11) | O33—Mo3—O32 | 108.10 (14) |
| O31iii—Mg1—O31iv | 81.22 (11) | O33—Mo3—O34 | 110.71 (13) |
| O13i—Mg2—O24 | 88.40 (12) | O32—Mo3—O34 | 109.21 (14) |
| O13i—Mg2—O22v | 90.10 (12) | O33—Mo3—O31 | 108.43 (13) |
| O24—Mg2—O22v | 175.47 (12) | O32—Mo3—O31 | 109.96 (13) |
| O13i—Mg2—O11vi | 92.52 (11) | O34—Mo3—O31 | 110.40 (12) |
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+2, −y+1, −z+1; (iii) x+1, y, z; (iv) −x+1, −y, −z+1; (v) x, y+1, z; (vi) x, y, z−1; (vii) x, y−1, z.
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Supplementary Materials
Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S205698901600829X/br2259sup1.cif
Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901600829X/br2259Isup2.hkl
CCDC reference: 1481125
Additional supporting information: crystallographic information; 3D view; checkCIF report