inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

Na4Fe2+Fe3+(PO4)3, a new synthetic NASICON-type phosphate

aUniversity of Liège, Laboratory of Mineralogy B.18, B-4000 Liège, Belgium
*Correspondence e-mail: fhatert@ulg.ac.be

(Received 25 February 2009; accepted 12 March 2009; online 19 March 2009)

This paper reports the crystal structure of tetra­sodium diiron tris(phosphate), Na4Fe2+Fe3+(PO4)3, which has been synthesized hydro­thermally at 773 K and 0.1 GPa. The crystal structure has been refined in the space group R[\overline{3}]c and is identical to that of γ-NASICON. The heteropolyhedral framework is based on a regular alternation, in three dimensions, of corner-sharing PO4 tetra­hedra and FeO6 octa­hedra, constituting so-called `lantern units' stacked along the c axis. The Na+ cations are distributed over two crystallographic sites: the six-coordinated Na1 site which lies between two `lantern units', and the eight-coordinated Na2 site which lies at the same z value as the P site.

Related literature

For general background, see: Hatert et al. (2006[Hatert, F., Fransolet, A.-M. & Maresch, W. V. (2006). Contrib. Mineral. Petrol. 152, 399-419.]); Hatert & Fransolet (2006[Hatert, F. & Fransolet, A.-M. (2006). Ber. Dtsch. Mineral. Ges. Beih. Eur. J. Mineral. 18, 53.]); Hatert (2007a[Hatert, F. (2007a). Z. Kristallogr. New Cryst. Struct. 221, 1-2.],b[Hatert, F. (2007b). 24th European Crystallographic Meeting (ECM-24). Abstract Book, p. s31.]). For related structures, see: Sljukic et al. (1969[Sljukic, M., Matkovic, B., Prodic, B. & Anderson, D. (1969). Z. Kristallogr. 130, 148-161.]); Masquelier et al. (2000[Masquelier, C., Wurm, C., Rodríguez-Carvajal, J., Gaubicher, J. & Nazar, L. (2000). Chem. Mater. 12, 525-532.]). For bond-valence calculations, see: Brown & Altermatt (1985[Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244-247.]). For the use of the pressure vessel, see: Tuttle (1949[Tuttle, O. F. (1949). Geol. Soc. Am. Bull. 60, 1727-1729.]). For the standard used in the chemical analysis, see: Fransolet (1975[Fransolet, A.-M. (1975). PhD thesis, University of Liège, Belgium.]). For software used to establish the space group, see: Le Page (1987[Le Page, Y. (1987). J. Appl. Cryst. 20, 264-269.]).

Experimental

Crystal data
  • Na4Fe2.(PO4)3

  • Mr = 488.57

  • Trigonal, [R \overline 3c ]

  • a = 8.9543 (9) Å

  • c = 21.280 (4) Å

  • V = 1477.6 (4) Å3

  • Z = 6

  • Mo Kα radiation

  • μ = 3.68 mm−1

  • T = 293 K

  • 0.08 × 0.05 × 0.03 mm

Data collection
  • Bruker P4 diffractometer

  • Absorption correction: ψ scan (XSCANS; Siemens, 1991[Siemens (1991). XSCANS. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]) Tmin = 0.693, Tmax = 0.896

  • 721 measured reflections

  • 294 independent reflections

  • 284 reflections with I > 2σ(I)

  • Rint = 0.021

  • 3 standard reflections every 97 reflections intensity decay: 1.9%

Refinement
  • R[F2 > 2σ(F2)] = 0.052

  • wR(F2) = 0.125

  • S = 1.40

  • 294 reflections

  • 35 parameters

  • Δρmax = 1.70 e Å−3

  • Δρmin = −0.97 e Å−3

Data collection: XSCANS (Siemens, 1991[Siemens (1991). XSCANS. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); cell refinement: XSCANS; data reduction: SHELXTL-Plus (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ATOMS (Dowty, 1993[Dowty, E. (1993). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA.]); software used to prepare material for publication: SHELXTL-Plus.

Supporting information


Comment top

In the natural geological environment of granitic pegmatites, Na–Fe–Mn-bearing phosphates play important geochemical and petrological roles. The alluaudite group of minerals, with an idealized chemical composition Na2(Mn,Fe2+)2Fe3+(PO4)3, constitutes a good example of primary phosphates which can be used as geothermometer, or to constrain the oxygen fugacity which prevailed in granitic pegmatites (Hatert et al., 2006). In order to better understand the crystallization conditions of iron-rich alluaudites in pegmatites, we decided to investigate the Na–Fe2+–Fe3+ (+PO4) ternary system by hydrothermal methods (Hatert & Fransolet, 2006). These experiments produced several new phosphates, which crystallized in the Na-rich part of the system and were investigated by single-crystal X-ray diffraction techniques (Hatert, 2007a,b). Starting from the composition Na4Fe2+Fe3+(PO4)3, the hydrothermal synthesis at 500°C and 0.1 GPa produced large pink crystals; their crystal structure is reported herein.

The crystal structure of the title compound has been refined in space group R3c and corresponds to that of centrosymmetric γ-NASICON-type phosphates (Sljukic et al., 1969; Masquelier et al., 2000). The heteropolyhedral framework is based on the regular alternation, in the three dimensions, of corner-sharing PO4 tetrahedra (P—O = 1.533–1.538 Å) and FeO6 octahedra (Fe—O = 2.010–2.130 Å; Fig. 1), and shows the stacking, along the c direction, of the so-called 'lantern units' (Masquelier et al., 2000). The monovalent Na+ cations are distributed over two crystallographic sites: the 6-coordinated Na1 site (Na1—O = 2.402 Å) which lies between two 'lantern units', and the 8-coordinated Na2 site (Na2—O = 2.487–2.990 Å) which lies at the same z value as the P atom (Fig. 2).

Bond-valence sums were calculated for each ion using the parameters of Brown & Altermatt (1985). The P1 bond-valence sum is 4.99, and the O-atom bond-valence sums are within the normal acceptable range (1.93–2.10). The bond-valence sums also confirm that the Na1 and Na2 sites are filled by Na (0.98–1.19), and that the Fe1 site contains an equal amount of Fe2+ and Fe3+ (2.54).

A comparison with the crystal structure of γ-Na3Fe2(PO4)3 (Masquelier et al., 2000) shows that the two phosphates are isostructural. However, the amount of Na in the title compound reaches 4 atoms per formula unit, and is higher than the Na-content of any other known NASICON-type phosphate. This high Na-content is necessary to maintain charge balance, since the Fe1 site is occupied by 50% Fe2+ and 50% Fe3+. Na atoms are located on the same positions as in γ-Na3Fe2(PO4)3, but the two Na1 and Na2 sites are completely filled by Na atoms in the title compound, whereas their occupancy factors are 0.85 (3) (Na1) and 0.72 (3) (Na2) in γ-Na3Fe2(PO4)3 (Masquelier et al., 2000).

Masquelier et al. (2000) demonstrated that the size of the Na1 cavity is increased as this site is depopulated, and that this increase has a direct influence on the value of the c unit-cell parameter. This hypothesis is corroborated by our structural data, which show that a full occupancy of the Na1 site in Na4Fe2+Fe3+(PO4)3 induces small values for the Na1—O distances and for the c parameter (2.402 and 21.280 Å, respectively), while a partial occupancy of this site in γ-Na3Fe2(PO4)3 induces larger values for these parameters (2.500 and 21.808 Å, respectively; Masquelier et al., 2000). The presence of significant amounts of Fe2+ in the Fe1 site of the title compound also induces a significant increase of the Fe1—O average bond length (2.070 Å), when compared to the Fe1—O bond length reported for γ-Na3Fe2(PO4)3 (2.002 Å; Masquelier et al., 2000). This increase does not affect the c unit-cell parameter, but induces a significant increase of the a parameter, from 8.727 Å in γ-Na3Fe2(PO4)3 (Masquelier et al., 2000), to 8.954 Å in the title compound.

Related literature top

For general background, see: Hatert et al. (2006); Hatert & Fransolet (2006); Hatert (2007a,b). For related structures, see: Sljukic et al. (1969); Masquelier et al. (2000). For bond-valence calculations, see: Brown & Altermatt (1985). For the use of the pressure vessel, see: Tuttle (1949). For the standard used in the chemical analysis, see: Fransolet (1975). For software used to establish the space group, see: Le Page (1987). [Please check four added references and added text]

Experimental top

The title compound was synthesized under hydrothermal conditions. The starting material was prepared by mixing NaH2PO4.H2O, Na2HPO4.2H2O, FeO and Fe2O3 in proportions 2:1:1:1/2. About 25 mg of the homogenized mixture was sealed into a gold tube with an outer diameter of 2 mm and a length of 25 mm, containing 2 mg of distilled water. The gold capsule was then inserted in a Tuttle-type pressure vessel (Tuttle, 1949) and maintained at a temperature of 500°C and a pressure of 0.1 GPa. After 3 d, the sample still in the gold tube in the autoclave, was quenched to room temperature in a stream of cold air. The synthesized phosphates consisted of large pink crystals of the title compound, associated with colourless crystals of maricite, NaFe2+(PO4), and with isometric black crystals of Na7Fe4(PO4)6.

A chemical analysis of the title compound has been performed with a CAMEBAX SX-50 electron microprobe (15 kV acceleration voltage, 20 nA beam current, analyst H.-J. Bernhardt, Ruhr-Universität Bochum, Germany). The standards used were graftonite from Kabira (sample KF16; Fransolet, 1975) (Fe, P), and jadeite (Na). The average of 6 point analyses gives P2O5 42.47, FeO* 16.94, Fe2O3* 14.17, Na2O 24.47, total 98.05 wt. % (* values calculated to maintain charge balance). The chemical composition, calculated on the basis of 3 P, corresponds to Na3.96Fe2+1.18Fe3+0.89(PO4)3.

Refinement top

A first refinement in space group R3 converged to a satisfactory model with R1 = 0.0328, but a check of these structural data with the program ADDSYM (Le Page, 1987) immediately allowed to identify supplementary symmetry elements, thus confirming the space group R3c. All atoms were refined anisotropically, and a preliminary refinement of the site occupancy factors of Na1 and Na2 confirmed that these sites were filled with Na atoms only. In the final refinement cycle, the Na1 and Na2 site occupancy factors were consequently constrained to 1.0.

Computing details top

Data collection: XSCANS (Siemens, 1991); cell refinement: XSCANS (Siemens, 1991); data reduction: SHELXTL-Plus (Sheldrick, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: SHELXTL-Plus (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Fragment of the Na4Fe2+Fe3+(PO4)3 structure (50% displacement ellipsoids) showing the bonding environments of the Fe and P cations. [Symmetry codes: (i) 2/3 + x - y, 1/3 - y, 1/3 - z; (ii) 2/3 - x, 1/3 - x + y, 1/3 - z; (iii) 2/3 + y, 1/3 + x, 1/3 - z; (iv) x, -y - 1/3, z; (v) x, x - y, 1/6 -z; (vi) 1/3 + y, 2/3 - x + y, 1/6 - z; (vii) 2/3 - y, 1/3 + x - y, z - 1/6; (viii) -y, -x, z; (ix) x + 2/3, y + 1/3, 1/3 - z.]
[Figure 2] Fig. 2. Polyhedral view of the Na4Fe2+Fe3+(PO4)3 structure. FeO6 octahedra are shown with light shading, PO4 tetrahedra with dark shading, Na1 as small circles, and Na2 as large circles.
Tetrasodium diiron tris(phosphate) top
Crystal data top
Na3.96Fe2.07(PO4)3Dx = 3.294 Mg m3
Mr = 488.57Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3cCell parameters from 35 reflections
Hall symbol: -R 3 2"cθ = 5.9–12.6°
a = 8.9543 (9) ŵ = 3.68 mm1
c = 21.280 (4) ÅT = 293 K
V = 1477.6 (4) Å3Isometric crystal, pink
Z = 60.08 × 0.05 × 0.03 mm
F(000) = 1422
Data collection top
Bruker P4
diffractometer
284 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.021
Graphite monochromatorθmax = 25.0°, θmin = 3.3°
ω scansh = 101
Absorption correction: ψ scan
(XSCANS; Siemens, 1991)
k = 110
Tmin = 0.693, Tmax = 0.896l = 251
721 measured reflections3 standard reflections every 97 reflections
294 independent reflections intensity decay: 1.9%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.052 w = 1/[σ2(Fo2) + (0.0415P)2 + 5P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.125(Δ/σ)max < 0.001
S = 1.40Δρmax = 1.70 e Å3
294 reflectionsΔρmin = 0.97 e Å3
35 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0027 (6)
Crystal data top
Na3.96Fe2.07(PO4)3Z = 6
Mr = 488.57Mo Kα radiation
Trigonal, R3cµ = 3.68 mm1
a = 8.9543 (9) ÅT = 293 K
c = 21.280 (4) Å0.08 × 0.05 × 0.03 mm
V = 1477.6 (4) Å3
Data collection top
Bruker P4
diffractometer
284 reflections with I > 2σ(I)
Absorption correction: ψ scan
(XSCANS; Siemens, 1991)
Rint = 0.021
Tmin = 0.693, Tmax = 0.8963 standard reflections every 97 reflections
721 measured reflections intensity decay: 1.9%
294 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.05235 parameters
wR(F2) = 0.1250 restraints
S = 1.40Δρmax = 1.70 e Å3
294 reflectionsΔρmin = 0.97 e Å3
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Fe10.00000.00000.14926 (9)0.0082 (8)
P10.33330.3672 (3)0.08330.0080 (9)
Na10.00000.00000.00000.0129 (17)
Na20.33330.0278 (7)0.08330.0262 (13)
O10.1950 (8)0.2066 (9)0.1913 (3)0.0213 (15)
O20.1869 (8)0.0152 (7)0.0838 (3)0.0135 (14)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe10.0070 (8)0.0070 (8)0.0105 (11)0.0035 (4)0.0000.000
P10.0041 (15)0.0109 (12)0.0065 (14)0.0021 (7)0.0000 (10)0.0000 (5)
Na10.009 (2)0.009 (2)0.020 (4)0.0047 (12)0.0000.000
Na20.013 (3)0.029 (2)0.031 (3)0.0065 (13)0.001 (2)0.0005 (11)
O10.015 (3)0.032 (4)0.013 (3)0.008 (3)0.006 (2)0.008 (3)
O20.012 (3)0.019 (3)0.012 (3)0.010 (3)0.004 (2)0.006 (2)
Geometric parameters (Å, º) top
Fe1—O12.010 (6)Na1—O2vii2.402 (5)
Fe1—O1i2.010 (6)Na1—O2i2.402 (5)
Fe1—O1ii2.010 (6)Na1—O2ii2.402 (5)
Fe1—O2i2.130 (6)Na1—O2viii2.402 (5)
Fe1—O22.130 (6)Na2—O2i2.487 (8)
Fe1—O2ii2.130 (6)Na2—O2v2.487 (8)
P1—O1iii1.533 (6)Na2—O2ii2.493 (6)
P1—O1iv1.533 (6)Na2—O2ix2.493 (6)
P1—O2i1.538 (6)Na2—O1ix2.534 (6)
P1—O2v1.538 (6)Na2—O1ii2.534 (6)
Na1—O2vi2.402 (5)Na2—O1x2.990 (8)
Na1—O22.402 (5)Na2—O1xi2.990 (8)
O1—Fe1—O1i101.7 (2)O2—Na1—O2viii109.0 (2)
O1—Fe1—O1ii101.7 (2)O2vii—Na1—O2viii71.0 (2)
O1i—Fe1—O1ii101.7 (2)O2i—Na1—O2viii180.00 (17)
O1—Fe1—O2i165.5 (2)O2ii—Na1—O2viii109.0 (2)
O1i—Fe1—O2i86.5 (2)O2i—Na2—O2v60.5 (3)
O1ii—Fe1—O2i88.1 (2)O2i—Na2—O2ii68.1 (3)
O1—Fe1—O286.5 (2)O2v—Na2—O2ii128.6 (2)
O1i—Fe1—O288.1 (2)O2i—Na2—O2ix128.6 (2)
O1ii—Fe1—O2165.5 (2)O2v—Na2—O2ix68.1 (3)
O2i—Fe1—O281.8 (2)O2ii—Na2—O2ix163.3 (4)
O1—Fe1—O2ii88.1 (2)O2i—Na2—O1ix93.1 (2)
O1i—Fe1—O2ii165.5 (2)O2v—Na2—O1ix70.0 (2)
O1ii—Fe1—O2ii86.5 (2)O2ii—Na2—O1ix114.28 (19)
O2i—Fe1—O2ii81.8 (2)O2ix—Na2—O1ix68.73 (19)
O2—Fe1—O2ii81.8 (2)O2i—Na2—O1ii70.0 (2)
O1iii—P1—O1iv109.6 (5)O2v—Na2—O1ii93.1 (2)
O1iii—P1—O2i106.9 (3)O2ii—Na2—O1ii68.73 (19)
O1iv—P1—O2i112.1 (3)O2ix—Na2—O1ii114.28 (19)
O1iii—P1—O2v112.1 (3)O1ix—Na2—O1ii160.8 (4)
O1iv—P1—O2v106.9 (3)O2i—Na2—O1x113.49 (19)
O2i—P1—O2v109.2 (5)O2v—Na2—O1x154.86 (18)
O2vi—Na1—O2180.0 (3)O2ii—Na2—O1x52.52 (18)
O2vi—Na1—O2vii71.0 (2)O2ix—Na2—O1x112.9 (3)
O2—Na1—O2vii109.0 (2)O1ix—Na2—O1x86.74 (13)
O2vi—Na1—O2i109.0 (2)O1ii—Na2—O1x108.0 (2)
O2—Na1—O2i71.0 (2)O2i—Na2—O1xi154.86 (18)
O2vii—Na1—O2i109.0 (2)O2v—Na2—O1xi113.49 (19)
O2vi—Na1—O2ii109.0 (2)O2ii—Na2—O1xi112.9 (3)
O2—Na1—O2ii71.0 (2)O2ix—Na2—O1xi52.52 (18)
O2vii—Na1—O2ii180.0 (3)O1ix—Na2—O1xi108.0 (2)
O2i—Na1—O2ii71.0 (2)O1ii—Na2—O1xi86.74 (13)
O2vi—Na1—O2viii71.0 (2)O1x—Na2—O1xi82.0 (3)
Symmetry codes: (i) x+y, x, z; (ii) y, xy, z; (iii) x+y1/3, y2/3, z1/6; (iv) xy1/3, x2/3, z+1/3; (v) xy2/3, y1/3, z+1/6; (vi) x, y, z; (vii) y, x+y, z; (viii) xy, x, z; (ix) y2/3, x1/3, z+1/6; (x) x1/3, xy+1/3, z1/6; (xi) x1/3, y+1/3, z+1/3.

Experimental details

Crystal data
Chemical formulaNa3.96Fe2.07(PO4)3
Mr488.57
Crystal system, space groupTrigonal, R3c
Temperature (K)293
a, c (Å)8.9543 (9), 21.280 (4)
V3)1477.6 (4)
Z6
Radiation typeMo Kα
µ (mm1)3.68
Crystal size (mm)0.08 × 0.05 × 0.03
Data collection
DiffractometerBruker P4
diffractometer
Absorption correctionψ scan
(XSCANS; Siemens, 1991)
Tmin, Tmax0.693, 0.896
No. of measured, independent and
observed [I > 2σ(I)] reflections
721, 294, 284
Rint0.021
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.052, 0.125, 1.40
No. of reflections294
No. of parameters35
Δρmax, Δρmin (e Å3)1.70, 0.97

Computer programs: XSCANS (Siemens, 1991), SHELXTL-Plus (Sheldrick, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS (Dowty, 1993).

 

Acknowledgements

Many thanks are due to A.-M. Fransolet for his constructive comments on the first version of this manuscript and to H.-J. Bernhardt, Ruhr-Universität Bochum, Germany, for the chemical analysis. The author also thanks the FRS–FNRS (Belgium) for a position as `Chercheur qualifié' and for grant Nos. 1.5.113.05.F and 1.5.098.06.F, as well as the Alexander von Humboldt Foundation (Germany) for a research fellowship at the Ruhr-Universität Bochum during the 2004–2005 academic year.

References

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