Crystal structure of a sodium, zinc and iron(III)-based non-stoichiometric phosphate with an alluaudite-like structure: Na1.67Zn1.67Fe1.33(PO4)3

Khmiyas, J.; Assani, A.; Saadi, M.; El Ammari, L.

doi:10.1107/S2056989015009767

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ISSN: 2056-9890

Volume 71| Part 6| June 2015| Pages 690-692

doi:10.1107/S2056989015009767

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Crystal structure of a sodium, zinc and iron(III)-based non-stoichiometric phosphate with an alluaudite-like structure: Na_1.67Zn_1.67Fe_1.33(PO₄)₃

Jamal Khmiyas,^a ^* Abderrazzak Assani,^a Mohamed Saadi ^a and Lahcen El Ammari ^a

^aLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Université Mohammed V, Avenue Ibn Battouta, BP 1014, Rabat, Morocco
^*Correspondence e-mail: j_khmiyas@yahoo.fr

Edited by S. Parkin, University of Kentucky, USA (Received 4 May 2015; accepted 20 May 2015; online 23 May 2015)

The new title compound, disodium dizinc iron(III) tris(phosphate), Na_1.67Zn_1.67Fe_1.33(PO₄)₃, which belongs to the alluaudite family, has been synthesized by solid-state reactions. In this structure, all atoms are in general positions except for four, which are located on special positions of the C2/c space group. This structure is characterized by cation substitutional disorder at two sites, one situated on the special position 4e (2) and the other on the general position 8f. The 4e site is partially occupied by Na⁺ [0.332 (3)], whereas the 8f site is entirely filled by a mixture of Fe and Zn. The full-occupancy sodium and zinc atoms are located at the Wyckoff positions on the inversion center 4a (-1) and on the twofold rotation axis 4e, respectively. Refinement of the occupancy ratios, bond-valence analysis and the electrical neutrality requirement of the structure lead to the given composition for the title compound. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octahedra stacked parallel to [10-1]. The chains are formed by a succession of trimers based on [ZnO₆] octahedra and the mixed-cation Fe^III/Zn^II [(Fe/Zn)O₆] octahedra [Fe^III:Zn^III ratio 0.668 (3)/0.332 (3)]. Continuous chains are held together by PO₄ phosphate groups, forming polyhedral sheets perpendicular to [010]. The stacked sheets delimit two types of tunnels parallel to the c axis in which the sodium cations are located. Each Na⁺ cation is coordinated by eight O atoms. The disorder of Na in the tunnel might presage ionic mobility for this material.

Keywords: crystal structure; transition-metal phosphates; solid-state reaction synthesis; alluaudite structure type; Na_1.67Zn_1.67Fe_1.33(PO₄)₃.

CCDC reference: 1402019

1. Chemical context

Alkali transition-metal phosphates belonging to the alluaudite family constitute one of the most diverse and rich classes of minerals, and have been studied intensively over the last few years. Owing to their outstanding physico-chemical properties, these compounds have many potential applications in various fields, such as catalytic activity (Kacimi et al., 2005 ) and as promising cathodes for sodium-ion batteries through the presence of mobile cations located in the tunnels of the open three-dimensional framework (Huang et al., 2015 ). In their recent study, Huang et al. (2015) point out that the electrochemical performance is not only associated with morphology, but also with the electronic and crystalline structure.

Accordingly, a large number of alluaudite phases with alkali cations in the tunnels have been reported. Nevertheless, the presence of alkali metals in the tunnels of synthetic alluaudite phases is frequently accompanied by cationic distributions that lead to non-stoichiometric compositions, such as: (Na_0.38,Ca_0.31)MgFe₂(PO₄)₃ (Zid et al., 2005 ); NaFe_3.67(PO₄)₃ (Korzenski et al., 1998 ); Cu_1.35Fe₃(PO₄)₃ (Warner et al., 1993 ); K_0.53Mn_2.37Fe_1.24(PO₄)₃ (Hidouri & Ben Amara, 2011 ); Na_1.79Mg_1.79Fe_1.21(PO₄)₃ (Hidouri et al., 2003 ); Na_1.50Mn_2.48Al_0.85(PO₄)₃ (Hatert, 2006 ); Na_1−xLi_xMnFe₂(PO₄)₃ where x = 0, 0.25, 0.50, and 0.75 (Hermann et al., 2002 ). As part of our study on alluaudite-related phosphates (Bouraima et al., 2015 ; Assani et al., 2011 ), we report the synthesis and the crystal structure of a new sodium, zinc and iron-based non-stoichiometric phosphate, namely Na_1.67Zn_1.67Fe_1.33(PO₄)₃.

2. Structural commentary

The alluaudite structure of the title compound crystallizes in the monoclinic space group C2/c, with Z = 4. The principal building units of the crystal structure are represented in Fig. 1. Refinement of the occupancy fractions, bond-valence analysis based on the formula proposed by Brown & Altermatt (1985 ) and the required electrical neutrality of the structure lead to the formula Na_1.67Zn_1.67Fe_1.33(PO₄)₃ for the title compound. The mixed Fe1 and Zn1 atoms are located at the general position 8f with Fe³⁺/Zn²⁺ occupancy fractions of 0.668 (3)/0.332 (3), and form a highly distorted [(Fe1/Zn1)O₆] octahedral group, with Fe³⁺/Zn²⁺—O bond lengths ranging from 1.951 (1) to 2.209 (1)Å. The Zn2 atom is surrounded by six oxygen atoms, building a slightly distorted octahedron with an average Zn2—O bond length of 2.153 (1) Å.

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 + $[{1\over 2}]$ , y + $[{1\over 2}]$ , z; (ii) −x + $[{3\over 2}]$ , y + $[{1\over 2}]$ , −z + $[{1\over 2}]$ ; (iii) −x + $[{3\over 2}]$ , −y + $[{3\over 2}]$ , −z + 1; (iv) −x + $[{3\over 2}]$ , −y + $[{3\over 2}]$ , −z; (v) −x + 1, −y + 1, −z; (vi) −x + 1, y, −z + $[{1\over 2}]$ ; (vii) x, −y + 1, z + $[{1\over 2}]$ ; (viii) x − $[{1\over 2}]$ , −y + $[{3\over 2}]$ , z − $[{1\over 2}]$ ; (ix) −x + 2, y, −z + $[{3\over 2}]$ ; (x) −x + 2, −y + 1, −z + 1; (xi) x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z + $[{1\over 2}]$ ; (xii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , −z + 1; (xiii) x, −y + 1, z − $[{1\over 2}]$ .]

The crystal structure of this phosphate compound consists of infinite kinked chains of two edge-sharing [Fe1/Zn1O₆] octahedra leading to the formation of [(Fe1,Zn1)₂O₁₀] dimers that are connected by a common edge to [Zn2O₆] octahedra, as shown in Fig. 2. These chains are linked by PO₄ tetrahedral groups, forming a stack of sheets perpendicular to [010] and alternating with sodium layers, as shown in Fig. 3, which reveal small tunnels along the [201] direction. The three-dimensional framework also encloses two types of large tunnels, in which the Na⁺ cations reside, as shown in Fig. 4. The site 4e centred on the first tunnel is partially occupied by Na1 [0.332 (3)], whereas Na2 occupies site 4a centred on the second tunnel. Each sodium atom is surrounded by eight oxygen atoms with Na1—O and Na2—O bond lengths in the ranges 2.448 (1)–2.908 (2) Å, and 2.324 (1)–2.901 (1) Å, respectively. The displacement ellipsoids of the partially occupied atom Na1 are rather larger than those of the rest of the atoms. Most probably this is due to the size of the channels, which allows atom Na1 to have more freedom. The disorder of Na in the tunnel may presage ionic mobility for this material.

Figure 2
A view along the b axis of a sheet resulting from chains connected by vertices of PO₄ tetrahedra.

Figure 3
A stack of layers perpendicular to the b axis, showing small tunnels along the [201] direction.

Figure 4
Polyhedral representation of Na_1.67Zn_1.67Fe_1.33(PO₄)₃ showing tunnels running along the [001] direction.

3. Synthesis and crystallization

Single crystals of Na_1.67Zn_1.67Fe_1.33(PO₄)₃ were synthesised by conventional solid-state reaction (Girolami et al., 1999 ). The nitrate-based sodium, zinc and iron precursors, in addition to the 85 wt% H₃PO₄ were taken in proportions corresponding to the molar ratio Na:Zn:Fe:P = 2:2:1:3. The resulting reaction mixture was ground in an agate mortar and progressively heated in a platinum crucible to the melting temperature of 1135 K. The melted product was cooled at a rate of 5 K/h. The product was obtained as transparent brown crystals corresponding to the title phosphate.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. Refinements of the site-occupancy factors of the metal site 8f revealed the ratio of Fe1:Zn1 = 0.668 (3):0.332 (3), whereas the the occupancy fraction of Na1 was constrained to that of Zn1 in order to maintain electrical neutrality. The highest peak and the deepest hole in the final difference Fourier map are at 0.72 and 0.40 Å from O1 and Zn2, respectively.

Table 1
Experimental details

Crystal data
Chemical formula	Na_1.67Zn_1.67Fe_1.33(PO₄)₃
M_r	506.59
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	11.7545 (4), 12.5080 (4), 6.4014 (2)
β (°)	113.507 (1)
V (Å³)	863.06 (5)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	7.52
Crystal size (mm)	0.31 × 0.25 × 0.19

Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Bruker, 2009 )
T_min, T_max	0.504, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	18880, 2101, 1997
R_int	0.031
(sin θ/λ)_max (Å⁻¹)	0.833

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.017, 0.046, 1.19
No. of reflections	2101
No. of parameters	96
Δρ_max, Δρ_min (e Å⁻³)	0.65, −1.21
Computer programs: APEX2 and SAINT (Bruker, 2009), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), ORTEPIII (Burnett & Johnson, 1996 ), ORTEP-3 for Windows Farrugia, 2012 ), DIAMOND (Brandenburg, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1402019

Crystal structure: contains datablock I. DOI: 10.1107/S2056989015009767/pk2551sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015009767/pk2551Isup2.hkl

checkCIF report

Chemical context top

Alkali transition-metal phosphates belonging to the alluaudite family constitute one of the most diverse and rich classes of minerals, and have been studied intensively over the last few years. Owing to their outstanding physico-chemical properties, these compounds have many potential applications in various fields, such as catalytic activity (Kacimi et al., 2005) and as promising cathodes for sodium-ion batteries through the presence of mobile cations located in the tunnels of the open three-dimensional framework (Huang et al., 2015). In their recent study, Huang et al. (2015) point out that the electrochemical performance is not only associated with morphology, but also with electronic and crystalline structure.

Accordingly, a large number of alluaudite phases with alkali cations in the tunnels have been reported. Nevertheless, the presence of alkali metals in the tunnels of synthetic alluaudite phases is frequently accompanied by cationic distributions that lead to non-stoichiometric compositions, such as: (Na_0.38,Ca_0.31)MgFe₂(PO₄)₃ (Zid et al., 2005); NaFe_3.67(PO₄)₃ (Korzenski et al., 1998); Cu_1.35Fe₃(PO₄)₃ (Warner et al., 1993); K_0.53Mn_2.37Fe_1.24(PO₄)₃ (Hidouri & Ben Amara, 2011); Na_1.79Mg_1.79Fe_1.21(PO₄)₃ (Hidouri et al., 2003); Na_1.50Mn_2.48Al_0.85(PO₄)₃ (Hatert, 2006); Na_1-_xLi_xMnFe₂(PO₄)₃ where x = 0, 0.25, 0.50, and 0.75 (Hermann et al., 2002). As part of our study on alluaudite-related phosphates (Bouraima et al., 2015; Assani et al., 2011), we report the synthesis and the crystal structure of a new sodium, zinc and iron-based non-stoichiometric phosphate, namely Na_1.67Zn_1.67Fe_1.33(PO₄)₃.

Structural commentary top

The alluaudite structure of the title compound crystallizes in the monoclinic space group C2/c, with Z = 4. The principal building units of the crystal structure are represented in Fig. 1. Refinement of the occupancy fractions, bond-valence analysis based on the formula proposed by Brown & Altermatt (1985) and the required electrical neutrality of the structure lead to the formula Na_1.67Zn_1.67Fe_1.33(PO₄)₃ for the title compound. The mixed Fe1 and Zn1 atoms are located at the general position 8f with Fe³⁺/Zn²⁺ occupancy fractions of 0.668 (3)/0.332 (3), and form a highly distorted [(Fe1/Zn1)O₆] octahedral group, with Fe³⁺/Zn²⁺—O bond lengths ranging from 1.951 (1) to 2.209 (1)Å. The Zn2 atom is surrounded by six oxygen atoms, building a slightly distorted octahedron with an average Zn2—O bond length of 2.153 (1) Å.

Synthesis and crystallization top

Single crystals of Na_1.67Zn_1.67Fe_1.33(PO₄)₃ were synthesised by conventional solid-state reaction (Girolami et al., 1999). The nitrate-based sodium, zinc and iron precursors, in addition to the 85 wt% H₃PO₄ were taken in proportions corresponding to the molar ratio Na:Zn:Fe:P = 2:2:1:3. The resulting reaction mixture was ground in an agate mortar and progressively heated in a platinum crucible to the melting temperature of 1135 K. The melted product was cooled at a rate of 5 K/h. The product was obtained as transparent gray [brown in CIF] crystals corresponding to the title phosphate.

Refinement top

Related literature top

For related literature, see: Assani et al. (2011); Bouraima et al. (2015); Brown & Altermatt (1985); Girolami et al. (1999); Hatert (2006); Hermann et al. (2002); Hidouri & Ben Amara (2011); Hidouri et al. (2003); Huang et al. (2015); Kacimi et al. (2005); Korzenski et al. (1998); Warner et al. (1993); Zid et al. (2005).

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 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 + 1/2, y + 1/2, z; (ii) -x + 3/2, y + 1/2, -z + 1/2; (iii) -x + 3/2, -y + 3/2, -z + 1; (iv) -x + 3/2, -y + 3/2, -z; (v) -x + 1, -y + 1, -z; (vi) -x + 1, y, -z + 1/2; (vii) x, -y + 1, z + 1/2; (viii) x - 1/2, -y + 3/2, z - 1/2; (ix) -x + 2, y, -z + 3/2; (x) -x + 2, -y + 1, -z + 1; (xi) x + 1/2, -y + 1/2, z + 1/2; (xii) -x + 3/2, -y + 1/2, -z + 1; (xiii) x, -y + 1, z - 1/2.
	Fig. 2. A view along b axis of a sheet resulting from chains connected by vertices of PO₄ tetrahedra.
	Fig. 3. A stack of layers perpendicular to the b axis, showing small tunnels along the [201] direction.
	Fig. 4. Polyhedral representation of Na_1.67Zn_1.67Fe_1.33(PO₄)₃ showing tunnels running along the [001] direction.

Disodium dizinc iron(III) tris(phosphate) top

Crystal data top

Na_1.67Zn_1.67Fe_1.33(PO₄)₃	F(000) = 977
M_r = 506.59	D_x = 3.904 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -c 2yc	Cell parameters from 2101 reflections
a = 11.7545 (4) Å	θ = 2.5–36.3°
b = 12.5080 (4) Å	µ = 7.52 mm⁻¹
c = 6.4014 (2) Å	T = 296 K
β = 113.507 (1)°	Block, brown
V = 863.06 (5) Å³	0.31 × 0.25 × 0.19 mm
Z = 4

Data collection top

Bruker X8 APEX diffractometer	2101 independent reflections
Radiation source: fine-focus sealed tube	1997 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.031
ϕ and ω scans	θ_max = 36.3°, θ_min = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −19→16
T_min = 0.504, T_max = 0.748	k = −20→20
18880 measured reflections	l = −10→10

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.016P)² + 1.8532P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.017	(Δ/σ)_max = 0.001
wR(F²) = 0.046	Δρ_max = 0.65 e Å⁻³
S = 1.19	Δρ_min = −1.20 e Å⁻³
2101 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
96 parameters	Extinction coefficient: 0.0027 (2)

Crystal data top

Na_1.67Zn_1.67Fe_1.33(PO₄)₃	V = 863.06 (5) Å³
M_r = 506.59	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 11.7545 (4) Å	µ = 7.52 mm⁻¹
b = 12.5080 (4) Å	T = 296 K
c = 6.4014 (2) Å	0.31 × 0.25 × 0.19 mm
β = 113.507 (1)°

Data collection top

Bruker X8 APEX diffractometer	2101 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	1997 reflections with I > 2σ(I)
T_min = 0.504, T_max = 0.748	R_int = 0.031
18880 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.017	96 parameters
wR(F²) = 0.046	0 restraints
S = 1.19	Δρ_max = 0.65 e Å⁻³
2101 reflections	Δρ_min = −1.20 e Å⁻³

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. Reflections were merged by SHELXL according to the crystal class for the calculation of statistics and refinement.

_reflns_Friedel_fraction is defined as the number of unique Friedel pairs measured divided by the number that would be possible theoretically, ignoring centric projections and systematic absences.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Fe1	0.71738 (2)	0.84648 (2)	0.12925 (3)	0.00552 (5)	0.668 (3)
Zn1	0.71738 (2)	0.84648 (2)	0.12925 (3)	0.00552 (5)	0.332 (3)
Zn2	0.5000	0.73133 (2)	0.2500	0.00966 (5)
P1	0.76212 (3)	0.60983 (2)	0.37448 (5)	0.00388 (6)
P2	0.5000	0.28835 (3)	0.2500	0.00330 (7)
Na1	1.0000	0.49141 (19)	0.7500	0.0356 (7)	0.664 (6)
Na2	0.5000	0.5000	0.0000	0.01511 (18)
O1	0.83510 (9)	0.66524 (7)	0.60760 (15)	0.00695 (15)
O2	0.77771 (9)	0.67779 (8)	0.18481 (15)	0.00760 (15)
O6	0.45837 (8)	0.21761 (8)	0.03327 (15)	0.00622 (15)
O3	0.62448 (9)	0.60224 (8)	0.32496 (16)	0.00806 (16)
O5	0.39712 (9)	0.36396 (8)	0.24820 (16)	0.00747 (16)
O4	0.82109 (10)	0.49950 (8)	0.38406 (18)	0.01105 (17)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Fe1	0.00523 (7)	0.00632 (7)	0.00583 (7)	−0.00082 (5)	0.00307 (5)	−0.00067 (5)
Zn1	0.00523 (7)	0.00632 (7)	0.00583 (7)	−0.00082 (5)	0.00307 (5)	−0.00067 (5)
Zn2	0.01124 (10)	0.00917 (10)	0.01083 (10)	0.000	0.00679 (8)	0.000
P1	0.00555 (12)	0.00355 (11)	0.00280 (11)	−0.00051 (9)	0.00192 (9)	−0.00023 (8)
P2	0.00319 (15)	0.00365 (15)	0.00256 (15)	0.000	0.00063 (12)	0.000
Na1	0.0167 (8)	0.0452 (13)	0.0345 (11)	0.000	−0.0008 (7)	0.000
Na2	0.0221 (4)	0.0079 (3)	0.0091 (3)	0.0024 (3)	−0.0004 (3)	0.0006 (3)
O1	0.0098 (4)	0.0072 (4)	0.0035 (3)	−0.0020 (3)	0.0022 (3)	−0.0015 (3)
O2	0.0090 (4)	0.0101 (4)	0.0043 (3)	−0.0022 (3)	0.0032 (3)	0.0013 (3)
O6	0.0057 (3)	0.0081 (4)	0.0044 (3)	−0.0004 (3)	0.0015 (3)	−0.0024 (3)
O3	0.0068 (4)	0.0083 (4)	0.0101 (4)	−0.0015 (3)	0.0044 (3)	−0.0006 (3)
O5	0.0055 (3)	0.0064 (3)	0.0092 (4)	0.0012 (3)	0.0016 (3)	−0.0029 (3)
O4	0.0147 (4)	0.0062 (4)	0.0125 (4)	0.0026 (3)	0.0057 (3)	−0.0019 (3)

Geometric parameters (Å, º) top

Fe1—O5ⁱ	1.9514 (10)	P2—O6	1.5510 (9)
Fe1—O4ⁱⁱ	1.9607 (10)	P2—O6^vi	1.5510 (9)
Fe1—O1ⁱⁱⁱ	2.0170 (10)	Na1—O4^ix	2.4476 (11)
Fe1—O2^iv	2.0567 (10)	Na1—O4	2.4476 (11)
Fe1—O6^v	2.0684 (9)	Na1—O4^x	2.5713 (12)
Fe1—O2	2.2091 (10)	Na1—O4^vii	2.5713 (12)
Zn2—O3^vi	2.1019 (10)	Na1—O1	2.812 (2)
Zn2—O3	2.1019 (10)	Na1—O1^ix	2.812 (2)
Zn2—O6^vii	2.1549 (10)	Na1—O6^xi	2.908 (2)
Zn2—O6^v	2.1549 (10)	Na1—O6^xii	2.908 (2)
Zn2—O1ⁱⁱⁱ	2.2028 (9)	Na2—O5^xiii	2.3239 (9)
Zn2—O1^viii	2.2028 (9)	Na2—O5^vi	2.3239 (9)
P1—O3	1.5225 (10)	Na2—O3	2.3823 (9)
P1—O4	1.5345 (10)	Na2—O3^v	2.3824 (9)
P1—O2	1.5518 (10)	Na2—O3^xiii	2.5179 (10)
P1—O1	1.5563 (9)	Na2—O3^vi	2.5179 (10)
P2—O5	1.5317 (10)	Na2—O5^v	2.9008 (10)
P2—O5^vi	1.5317 (10)	Na2—O5	2.9008 (10)

O5ⁱ—Fe1—O4ⁱⁱ	95.89 (4)	O4—Na1—O1	55.92 (4)
O5ⁱ—Fe1—O1ⁱⁱⁱ	109.05 (4)	O4^x—Na1—O1	114.04 (7)
O4ⁱⁱ—Fe1—O1ⁱⁱⁱ	88.00 (4)	O4^vii—Na1—O1	61.59 (4)
O5ⁱ—Fe1—O2^iv	87.13 (4)	O4^ix—Na1—O1^ix	55.92 (4)
O4ⁱⁱ—Fe1—O2^iv	101.39 (4)	O4—Na1—O1^ix	119.76 (8)
O1ⁱⁱⁱ—Fe1—O2^iv	160.53 (4)	O4^x—Na1—O1^ix	61.58 (4)
O5ⁱ—Fe1—O6^v	161.52 (4)	O4^vii—Na1—O1^ix	114.04 (7)
O4ⁱⁱ—Fe1—O6^v	100.93 (4)	O1—Na1—O1^ix	78.70 (7)
O1ⁱⁱⁱ—Fe1—O6^v	79.35 (4)	O4^ix—Na1—O6^xi	114.24 (8)
O2^iv—Fe1—O6^v	82.12 (4)	O4—Na1—O6^xi	70.35 (5)
O5ⁱ—Fe1—O2	79.41 (4)	O4^x—Na1—O6^xi	83.40 (5)
O4ⁱⁱ—Fe1—O2	173.23 (4)	O4^vii—Na1—O6^xi	101.22 (6)
O1ⁱⁱⁱ—Fe1—O2	88.95 (4)	O1—Na1—O6^xi	125.27 (3)
O2^iv—Fe1—O2	83.34 (4)	O1^ix—Na1—O6^xi	144.38 (3)
O6^v—Fe1—O2	84.43 (4)	O4^ix—Na1—O6^xii	70.35 (5)
O3^vi—Zn2—O3	79.62 (5)	O4—Na1—O6^xii	114.24 (8)
O3^vi—Zn2—O6^vii	92.79 (4)	O4^x—Na1—O6^xii	101.22 (6)
O3—Zn2—O6^vii	113.99 (4)	O4^vii—Na1—O6^xii	83.40 (5)
O3^vi—Zn2—O6^v	113.99 (4)	O1—Na1—O6^xii	144.38 (3)
O3—Zn2—O6^v	92.79 (4)	O1^ix—Na1—O6^xii	125.27 (3)
O6^vii—Zn2—O6^v	145.51 (5)	O6^xi—Na1—O6^xii	51.96 (5)
O3^vi—Zn2—O1ⁱⁱⁱ	164.40 (4)	O5^xiii—Na2—O5^vi	180.00 (3)
O3—Zn2—O1ⁱⁱⁱ	86.51 (4)	O5^xiii—Na2—O3	100.43 (3)
O6^vii—Zn2—O1ⁱⁱⁱ	86.30 (4)	O5^vi—Na2—O3	79.57 (3)
O6^v—Zn2—O1ⁱⁱⁱ	73.53 (3)	O5^xiii—Na2—O3^v	79.57 (3)
O3^vi—Zn2—O1^viii	86.51 (4)	O5^vi—Na2—O3^v	100.43 (3)
O3—Zn2—O1^viii	164.40 (4)	O3—Na2—O3^v	180.0
O6^vii—Zn2—O1^viii	73.53 (3)	O5^xiii—Na2—O3^xiii	107.29 (3)
O6^v—Zn2—O1^viii	86.30 (4)	O5^vi—Na2—O3^xiii	72.71 (3)
O1ⁱⁱⁱ—Zn2—O1^viii	108.06 (5)	O3—Na2—O3^xiii	113.43 (4)
O3—P1—O4	112.20 (6)	O3^v—Na2—O3^xiii	66.57 (4)
O3—P1—O2	108.58 (5)	O5^xiii—Na2—O3^vi	72.71 (3)
O4—P1—O2	109.36 (6)	O5^vi—Na2—O3^vi	107.29 (3)
O3—P1—O1	111.16 (6)	O3—Na2—O3^vi	66.57 (4)
O4—P1—O1	107.14 (6)	O3^v—Na2—O3^vi	113.43 (4)
O2—P1—O1	108.32 (5)	O3^xiii—Na2—O3^vi	180.00 (3)
O5—P2—O5^vi	103.73 (8)	O5^xiii—Na2—O5^v	53.55 (4)
O5—P2—O6	112.27 (5)	O5^vi—Na2—O5^v	126.45 (4)
O5^vi—P2—O6	109.00 (5)	O3—Na2—O5^v	85.32 (3)
O5—P2—O6^vi	109.00 (5)	O3^v—Na2—O5^v	94.68 (3)
O5^vi—P2—O6^vi	112.28 (5)	O3^xiii—Na2—O5^v	67.11 (3)
O6—P2—O6^vi	110.43 (7)	O3^vi—Na2—O5^v	112.89 (3)
O4^ix—Na1—O4	175.26 (12)	O5^xiii—Na2—O5	126.45 (4)
O4^ix—Na1—O4^x	79.21 (3)	O5^vi—Na2—O5	53.55 (4)
O4—Na1—O4^x	100.58 (3)	O3—Na2—O5	94.68 (3)
O4^ix—Na1—O4^vii	100.58 (3)	O3^v—Na2—O5	85.32 (3)
O4—Na1—O4^vii	79.20 (3)	O3^xiii—Na2—O5	112.89 (3)
O4^x—Na1—O4^vii	174.93 (11)	O3^vi—Na2—O5	67.11 (3)
O4^ix—Na1—O1	119.76 (8)	O5^v—Na2—O5	180.00 (3)

Symmetry codes: (i) x+1/2, y+1/2, z; (ii) −x+3/2, y+1/2, −z+1/2; (iii) −x+3/2, −y+3/2, −z+1; (iv) −x+3/2, −y+3/2, −z; (v) −x+1, −y+1, −z; (vi) −x+1, y, −z+1/2; (vii) x, −y+1, z+1/2; (viii) x−1/2, −y+3/2, z−1/2; (ix) −x+2, y, −z+3/2; (x) −x+2, −y+1, −z+1; (xi) x+1/2, −y+1/2, z+1/2; (xii) −x+3/2, −y+1/2, −z+1; (xiii) x, −y+1, z−1/2.

Experimental details

Crystal data
Chemical formula	Na_1.67Zn_1.67Fe_1.33(PO₄)₃
M_r	506.59
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	11.7545 (4), 12.5080 (4), 6.4014 (2)
β (°)	113.507 (1)
V (Å³)	863.06 (5)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	7.52
Crystal size (mm)	0.31 × 0.25 × 0.19

Data collection
Diffractometer	Bruker X8 APEX diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.504, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	18880, 2101, 1997
R_int	0.031
(sin θ/λ)_max (Å⁻¹)	0.833

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.017, 0.046, 1.19
No. of reflections	2101
No. of parameters	96
Δρ_max, Δρ_min (e Å⁻³)	0.65, −1.20

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows Farrugia, 2012) and DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010).

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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Volume 71| Part 6| June 2015| Pages 690-692

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