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Crystal structure of strontium dicobalt iron(III) tris­­(orthophosphate): SrCo2Fe(PO4)3

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aLaboratoire de Chimie du Solide Appliquée, Faculty of Sciences, Mohammed V University in Rabat, Avenue Ibn Battouta, BP 1014, Rabat, Morocco, and bDépartement de Chimie, Faculté des Sciences, Université des Sciences et Techniques de Masuku, BP 943, Franceville, Gabon
*Correspondence e-mail: adam_bouraima@yahoo.fr

Edited by S. Parkin, University of Kentucky, USA (Received 24 June 2016; accepted 12 July 2016; online 19 July 2016)

The title compound, SrCo2Fe(PO4)3, has been synthesized by a solid-state reaction. It crystallizes with the α-CrPO4 type structure. In this structure, all atoms are on special positions of the Imma space group, except for two O atoms which are located on general positions. The three-dimensional network in the crystal structure is made up of two types of layers stacked normal to (100). The first layer is built from two edge-sharing CoO6 octa­hedra, leading to the formation of Co2O10 dimers that are connected to two PO4 tetra­hedra by a common edge and corners. The second layer results from apex-sharing FeO6 octa­hedra and PO4 tetra­hedra, which form linear chains alternating with a zigzag chain of SrII cations. These layers are linked together by common vertices of PO4 tetra­hedra and FeO6 octa­hedra to form an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] where the SrII cations are located. Each SrII cation is surrounded by eight O atoms.

1. Chemical context

The phosphate literature includes important works on the structural study of transition metal phosphates. The basic framework is built from tetra­hedrally coordinated phospho­rus linked to transition metals M in various environments, such as MOn (n = 4, 5 or 6). The manner in which polyhedra are inter­connected generates important structure types with porous or lamellar set-ups that can exhibit inter­esting physical properties. Accordingly, widespread studies have been devoted to this family of compounds, stimulated by the wide range of potential and commercial applications of these materials. Examples include applications in catalysis, as ion exchangers and in the manufacture of lithium and sodium rechargeable batteries. One particular scientific area in our laboratory is focused on investigating new functional phosphates belonging to the alluaudite (Moore, 1971[Moore, P. B. (1971). Am. Mineral. 56, 1955-1975.]) or α-CrPO4 (Attfield et al., 1988[Attfield, J. P., Cheetham, A. K., Cox, D. E. & Sleight, A. W. (1988). J. Appl. Cryst. 21, 452-457.]) structure types, owing to their potential use as new cathode materials for battery devices (Trad et al., 2010[Trad, K., Carlier, D., Croguennec, L., Wattiaux, A., Ben Amara, M. & Delmas, C. (2010). Chem. Mater. 22, 5554-5562.]; Kim et al., 2014[Kim, J., Kim, H., Park, K.-Y., Park, Y.-U., Lee, S., Kwon, H.-S., Yoo, H.-I. & Kang, K. (2014). J. Mater. Chem. A, 2, 8632-8636.]; Huang et al., 2015[Huang, W., Li, B., Saleem, M. F., Wu, X., Li, J., Lin, J., Xia, D., Chu, W. & Wu, Z. (2015). Chem. Eur. J. 21, 851-860.]).

Our earlier hydro­thermal investigations were undertaken with the A2O–MO–P2O5 and M′O–MO–P2O5 systems (A = monovalent cations, M and M′ = divalent cations) with approximate molar ratios A:M:P = 2:3:3 and M′:M:P = 1:3:3, which characterize the alluaudite or α-CrPO4 phases. Those studies involved the synthesis and structural characterization of new phosphates such as Na2Co2Fe(PO4)3 (Bouraima et al., 2015[Bouraima, A., Assani, A., Saadi, M., Makani, T. & El Ammari, L. (2015). Acta Cryst. E71, 558-560.]) and Na1.67Zn1.67Fe1.33(PO4)3 (Khmiyas et al., 2015[Khmiyas, J., Assani, A., Saadi, M. & El Ammari, L. (2015). Acta Cryst. E71, 690-692.]) belonging to the alluaudite-type structure group. In addition, divalent and trivalent transition-metal-based phosphates, such as SrNi2Fe(PO4)3 (Ouaatta et al., 2015[Ouaatta, S., Assani, A., Saadi, M. & El Ammari, L. (2015). Acta Cryst. E71, 1255-1258.]) and MMnII2MnIII(PO4)3 (M = Pb, Sr, Ba) (Alhakmi et al., 2013a[Alhakmi, G., Assani, A., Saadi, M. & El Ammari, L. (2013a). Acta Cryst. E69, i40.],b[Alhakmi, G., Assani, A., Saadi, M., Follet, C. & El Ammari, L. (2013b). Acta Cryst. E69, i56.]; Assani et al., 2013[Assani, A., Saadi, M., Alhakmi, G., Houmadi, E. & El Ammari, L. (2013). Acta Cryst. E69, i60.]) have been shown to adopt the α-CrPO4 structure type.

In search of a new promising phosphate, a solid-state chemistry investigation of A2O–MO–M2O3–P2O5 systems was undertaken. The present work reports on synthesis and crystal structure of the new strontium cobalt iron phosphate, SrCo2Fe(PO4)3, which has the α-CrPO4 type structure.

2. Structural commentary

In the title phosphate, SrCo2Fe(PO4)3, all atoms are on special positions, except two oxygen atoms (O3, O4) which are on general positions of the Imma space group. Its three-dimensional structure is constructed on the basis of PO4 tetra­hedra, FeO6 and CoO6 octa­hedra, as shown in Fig. 1[link]. The connection between these polyhedra produces two types of layers stacked normal to (100). The first layer is built from two edge-sharing CoO6 octa­hedra, leading to the formation of Co2O10 dimers, which are connected to two PO4 tetra­hedra by a common edge and vertex, as shown in Fig. 2[link]. The second layer is formed by alternating FeO6 octa­hedra and PO4 tetra­hedra, which share corners, building linear chains that surround a zigzag chain of SrII cations (see Fig. 3[link]). The layers are joined by the apices of PO4 tetra­hedra and FeO6 octa­hedra, giving rise to an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] where the SrII cations are located, as shown in Fig. 4[link] and Fig. 5[link]. This structure is characterized by a stoichiometric composition in which the Sr atom is surrounded by eight oxygen atoms with Sr—O bond lengths that vary between 2.6561 (13) and 2.6690 (9)Å. The same Sr environment is observed in the manganese homologue phosphates, namely MMnII2MnIII(PO4)3 (M = Pb, Sr, Ba).

[Figure 1]
Figure 1
The principal building units in the structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) −x + 2, −y + [{3\over 2}], z + 1; (ii) x, y, z + 1; (iii) −x + 2, −y + [{3\over 2}], z; (iv) −x + [{3\over 2}], −y + 1, z + [{1\over 2}]; (v) x + [{1\over 2}], y + [{1\over 2}], z + [{1\over 2}]; (vi) −x + [{3\over 2}], y + [{1\over 2}], z + [{1\over 2}]; (ix) −x + [{3\over 2}], y, −z + [{1\over 2}]; (x) x, −y + 1, −z; (xi) −x + 1, y, z; (xii) x, −y + 1, −z + 1; (xiii) −x + 1, −y + 1, −z + 1;(xiv) x − [{1\over 2}], y, −z + [{1\over 2}].]
[Figure 2]
Figure 2
Edge-sharing [CoO6] octa­hedra forming a layer parallel to (100).
[Figure 3]
Figure 3
A view along the a axis, showing a layer resulting from chains connected via vertices of PO4 tetra­hedra and FeO6 octa­hedra, alternating with a zigzag chain of Sr atoms.
[Figure 4]
Figure 4
Polyhedral representation of SrCo2Fe(PO4)3, showing channels running along [100].
[Figure 5]
Figure 5
Polyhedral representation of SrCo2Fe(PO4)3, showing channels running along [010].

3. Synthesis and crystallization

The title phosphate, SrCo2Fe(PO4)3, was synthesized in a solid-state reaction by mixing nitrates of strontium, cobalt and iron along with NH4H2PO4, taken in the molar proportions Sr:Co:Fe:P = 1:2:1:3. After a series of heat treatments up to 873 K in a platinum crucible, inter­spersed with grinding, the reaction mixture was heated to the melt (1343 K). The molten product was then cooled to room temperature at 5 K/h. The resulting solid contained brown crystals of a suitable size for X-ray diffraction.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. The highest peak and the deepest hole in the final Fourier map are at 0.63 and 0.68 Å from Sr1 and P2, respectively.

Table 1
Experimental details

Crystal data
Chemical formula SrCo2Fe(PO4)3
Mr 546.24
Crystal system, space group Orthorhombic, Imma
Temperature (K) 296
a, b, c (Å) 10.4097 (2), 13.2714 (3), 6.5481 (2)
V3) 904.63 (4)
Z 4
Radiation type Mo Kα
μ (mm−1) 11.64
Crystal size (mm) 0.30 × 0.27 × 0.21
 
Data collection
Diffractometer Bruker X8 APEX
Absorption correction Multi-scan (SADABS; Krause et al., 2015[Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3-10.])
Tmin, Tmax 0.595, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections 10008, 1297, 1243
Rint 0.030
(sin θ/λ)max−1) 0.858
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.017, 0.046, 1.16
No. of reflections 1297
No. of parameters 54
Δρmax, Δρmin (e Å−3) 1.00, −0.74
Computer programs: APEX2 and SAINT (Bruker, 2009[Bruker (2009). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXT2014 (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2014 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), ORTEP-3 for Windows (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]), DIAMOND (Brandenburg, 2006[Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

The distinction between cobalt and iron by X-ray diffraction is nearly impossible. Therefore we have examined several crystallographic models during the crystal structure refinements of the title compound. Based on the stoichiometric ratio of 1:2 for iron and cobalt in the starting materials, we assumed the same ratio in the crystal structures with oxidation states of +II for cobalt and and +III for iron. The best model is obtained with Fe1 and Co1 atoms in the Wyckoff positions 4a (2/m) and 8g (2), respectively. This cationic distribution in this model corresponds to the stoichiometry of the expected compound, in addition to the electric neutrality in the structure in reasonable agreement with the final model.

Supporting information


Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Strontium dicobalt iron(III) tris(orthophosphate) top
Crystal data top
SrCo2Fe(PO4)3Dx = 4.011 Mg m3
Mr = 546.24Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, ImmaCell parameters from 1297 reflections
a = 10.4097 (2) Åθ = 3.1–37.6°
b = 13.2714 (3) ŵ = 11.64 mm1
c = 6.5481 (2) ÅT = 296 K
V = 904.63 (4) Å3Block, brown
Z = 40.30 × 0.27 × 0.21 mm
F(000) = 1036
Data collection top
Bruker X8 APEX
diffractometer
1297 independent reflections
Radiation source: fine-focus sealed tube1243 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.030
φ and ω scansθmax = 37.6°, θmin = 3.1°
Absorption correction: multi-scan
(SADABS; Krause et al., 2015)
h = 1717
Tmin = 0.595, Tmax = 0.747k = 2219
10008 measured reflectionsl = 1111
Refinement top
Refinement on F20 restraints
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0245P)2 + 0.761P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.017(Δ/σ)max < 0.001
wR(F2) = 0.046Δρmax = 1.00 e Å3
S = 1.16Δρmin = 0.74 e Å3
1297 reflectionsExtinction correction: SHELXL2014 (Sheldrick, 2014b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
54 parametersExtinction coefficient: 0.0131 (4)
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Sr11.00000.75000.59715 (3)0.00785 (6)
Co10.75000.63284 (2)0.25000.00537 (6)
Fe10.50000.50000.50000.00392 (7)
P11.00000.75000.09098 (8)0.00336 (9)
P20.75000.42747 (3)0.25000.00388 (7)
O11.00000.65633 (9)0.04439 (19)0.00660 (18)
O20.88277 (11)0.75000.23618 (18)0.00607 (18)
O30.71075 (8)0.36360 (6)0.06735 (14)0.00776 (14)
O40.63833 (7)0.50376 (6)0.29533 (14)0.00600 (13)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Sr10.00819 (9)0.01003 (10)0.00534 (9)0.0000.0000.000
Co10.00533 (9)0.00376 (10)0.00704 (10)0.0000.00073 (6)0.000
Fe10.00292 (11)0.00439 (13)0.00443 (12)0.0000.0000.00015 (9)
P10.00344 (18)0.0029 (2)0.0038 (2)0.0000.0000.000
P20.00410 (14)0.00365 (17)0.00388 (14)0.0000.00051 (10)0.000
O10.0081 (4)0.0045 (5)0.0073 (4)0.0000.0000.0017 (4)
O20.0046 (4)0.0073 (5)0.0063 (4)0.0000.0020 (3)0.000
O30.0094 (3)0.0075 (3)0.0064 (3)0.0017 (3)0.0003 (3)0.0023 (2)
O40.0050 (3)0.0057 (3)0.0074 (3)0.0013 (2)0.0021 (2)0.0006 (2)
Geometric parameters (Å, º) top
Sr1—O1i2.6561 (13)Fe1—O41.9678 (8)
Sr1—O1ii2.6561 (13)Fe1—O4xi1.9678 (8)
Sr1—O2iii2.6600 (12)Fe1—O4xii1.9678 (8)
Sr1—O22.6600 (12)Fe1—O4xiii1.9678 (8)
Sr1—O3iv2.6690 (9)Fe1—O1iv2.0950 (12)
Sr1—O3v2.6690 (9)Fe1—O1xiv2.0950 (12)
Sr1—O3vi2.6690 (9)P1—O1iii1.5268 (12)
Sr1—O3vii2.6690 (9)P1—O11.5268 (12)
Co1—O22.0824 (8)P1—O2iii1.5470 (12)
Co1—O2viii2.0824 (8)P1—O21.5470 (12)
Co1—O4ix2.0913 (8)P2—O31.5219 (9)
Co1—O42.0914 (8)P2—O3ix1.5219 (9)
Co1—O3x2.1183 (9)P2—O41.5698 (8)
Co1—O3iv2.1183 (9)P2—O4ix1.5698 (8)
O1i—Sr1—O1ii55.81 (5)O2viii—Co1—O3x84.14 (4)
O1i—Sr1—O2iii141.74 (2)O4ix—Co1—O3x89.21 (3)
O1ii—Sr1—O2iii141.74 (2)O4—Co1—O3x92.88 (3)
O1i—Sr1—O2141.74 (2)O2—Co1—O3iv84.14 (4)
O1ii—Sr1—O2141.74 (2)O2viii—Co1—O3iv93.94 (4)
O2iii—Sr1—O254.61 (5)O4ix—Co1—O3iv92.89 (3)
O1i—Sr1—O3iv109.21 (2)O4—Co1—O3iv89.21 (3)
O1ii—Sr1—O3iv78.48 (2)O3x—Co1—O3iv177.44 (5)
O2iii—Sr1—O3iv108.19 (3)O4—Fe1—O4xi94.07 (5)
O2—Sr1—O3iv63.77 (3)O4—Fe1—O4xii85.93 (5)
O1i—Sr1—O3v78.48 (2)O4xi—Fe1—O4xii180.0
O1ii—Sr1—O3v109.21 (2)O4—Fe1—O4xiii180.0
O2iii—Sr1—O3v63.77 (3)O4xi—Fe1—O4xiii85.93 (5)
O2—Sr1—O3v108.19 (3)O4xii—Fe1—O4xiii94.07 (5)
O3iv—Sr1—O3v171.61 (4)O4—Fe1—O1iv86.02 (3)
O1i—Sr1—O3vi78.48 (2)O4xi—Fe1—O1iv86.02 (3)
O1ii—Sr1—O3vi109.21 (2)O4xii—Fe1—O1iv93.98 (3)
O2iii—Sr1—O3vi108.19 (3)O4xiii—Fe1—O1iv93.98 (3)
O2—Sr1—O3vi63.77 (3)O4—Fe1—O1xiv93.98 (3)
O3iv—Sr1—O3vi68.78 (4)O4xi—Fe1—O1xiv93.98 (3)
O3v—Sr1—O3vi110.56 (4)O4xii—Fe1—O1xiv86.02 (3)
O1i—Sr1—O3vii109.21 (2)O4xiii—Fe1—O1xiv86.02 (3)
O1ii—Sr1—O3vii78.48 (2)O1iv—Fe1—O1xiv180.0
O2iii—Sr1—O3vii63.77 (3)O1iii—P1—O1109.01 (10)
O2—Sr1—O3vii108.19 (3)O1iii—P1—O2iii110.91 (3)
O3iv—Sr1—O3vii110.56 (4)O1—P1—O2iii110.91 (3)
O3v—Sr1—O3vii68.78 (4)O1iii—P1—O2110.91 (3)
O3vi—Sr1—O3vii171.61 (4)O1—P1—O2110.91 (3)
O2—Co1—O2viii83.39 (5)O2iii—P1—O2104.15 (9)
O2—Co1—O4ix103.68 (3)O3—P2—O3ix112.30 (7)
O2viii—Co1—O4ix170.65 (4)O3—P2—O4108.00 (5)
O2—Co1—O4170.65 (4)O3ix—P2—O4114.17 (5)
O2viii—Co1—O4103.68 (3)O3—P2—O4ix114.17 (5)
O4ix—Co1—O470.01 (4)O3ix—P2—O4ix108.00 (5)
O2—Co1—O3x93.94 (4)O4—P2—O4ix99.68 (6)
Symmetry codes: (i) x+2, y+3/2, z+1; (ii) x, y, z+1; (iii) x+2, y+3/2, z; (iv) x+3/2, y+1, z+1/2; (v) x+1/2, y+1/2, z+1/2; (vi) x+3/2, y+1/2, z+1/2; (vii) x+1/2, y+1, z+1/2; (viii) x+3/2, y+3/2, z+1/2; (ix) x+3/2, y, z+1/2; (x) x, y+1, z; (xi) x+1, y, z; (xii) x, y+1, z+1; (xiii) x+1, y+1, z+1; (xiv) x1/2, y, z+1/2.
 

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements and Mohammed V University, Rabat, Morocco, for the financial support.

References

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