Synthesis and crystal structure of calcium dizinc iron(III) tris­(orthophosphate), CaZn2Fe(PO4)3

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

doi:10.1107/S2056989016012421

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Volume 72| Part 9| September 2016| Pages 1260-1262

https://doi.org/10.1107/S2056989016012421

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Synthesis and crystal structure of calcium dizinc iron(III) tris(orthophosphate), CaZn₂Fe(PO₄)₃

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

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

Edited by T. J. Prior, University of Hull, England (Received 20 July 2016; accepted 1 August 2016; online 5 August 2016)

Single crystals of the title compound, CaZn₂Fe(PO₄)₃, were synthesized by conventional solid-state reaction. In the asymmetric unit, all atoms are located in fully occupied general positions of the P2₁/c space group. The zinc atoms are located on two crystallographically independent sites with tetrahedral and distorted triangular-based bipyramidal geometries. Two edge-sharing triangular bipyramidal ZnO₅ units form a dimer, which is linked to slightly deformed FeO₆ octahedra via a common edge. The resulting chains are interconnected through PO₄ tetrahedra to form a layer perpendicular to the b axis. Moreover, the remaining PO₄ and ZnO₄ tetrahedra are linked together through common vertices to form tapes parallel to the c axis and surrounding a chain of Ca²⁺ cations to build a sheet, also perpendicular to the b axis. The stacking of the two layers along the b axis leads to the resulting three-dimensional framework, which defines channels in which the Ca²⁺ cations are located, each cation being coordinated by seven oxygen atoms.

Keywords: crystal structure; CaZn₂Fe(PO₄)₃; transition metal phosphate; solid-state reaction synthesis.

CCDC reference: 1497218

1. Chemical context

Microporous compounds with an open anionic framework containing transition metals have been widely studied during recent years, especially iron phosphates, because of their potential applications in several fields such as gas sensing (Abdurahman et al., 2014 ), catalysis (Ai, 1999 ), as cathode materials for rechargeable lithium batteries (Masquelier et al., 1998 ), biocompatibility of glass fibres for tissue engineering (Ahmed et al., 2004 ), and immobilization of spent nuclear fuel (Mesko & Day, 1999 ). Metal phosphates with an open framework can exhibit different architectures such as linear-chain, layered and three-dimensional structures with channels or cavities where a variety of cations with different sizes, ratio and charges are accommodated. The occupancy of the allowed sites by cations can provide different properties such as remarkable flexibility, fast ionic conduction and low thermal expansion, mainly observed in the compounds belonging to the NASICON family with the general formula MM′₂P₃O₁₂ (where M = alkali metal, alkaline-earth metal or a vacant site and M′ = Zr, Ti, Hf, etc.; Senbhagaraman et al., 1993 ). In our previous hydrothermal investigations, a variety of compounds have been synthesized and characterized with different ratios of alkaline earth metal:P, viz. Sr₂Mn₃(HPO₄)₂(PO₄)₂ (Khmiyas et al., 2013 ), BaMn^II₂Mn^III(PO₄)₃ (Assani et al., 2013 ), Mg₇(PO₄)₂(HPO₄)₄ (Assani et al., 2011 ). In this context, our interest is focused on the synthesis of new iron orthophosphates with an open-framework structure. Accordingly, we have succeeded in synthesizing and structurally characterizing a new calcium, zinc and iron-based open-framework phosphate, namely CaZn₂Fe(PO₄)₃.

2. Structural commentary

All atoms in asymmetric unit of the title compound occupy general positions of the P2₁/c space group. The refinement of this model was very easy and lead to an ordered structure in which the zinc cations occupy two sites with different environments. The coordination numbers of all cations were confirmed by bond-valence-sum calculations (Brown & Altermatt, 1985 ). The obtained values for Ca^II+, Zn^II+, Fe^III+ and P^V+ are as expected, viz. Ca1 (1.93), Zn1 (2.00), Zn2 (1.91), Fe1 (3.04), P1 (5.11), P2 (4.97) and P3 (4.94). The crystal structure is build up from PO₄ and Zn1O₄ tetrahedra, distorted triangular-based bipyramidal Zn2O₅ and FeO₆ octahedra, as shown in Fig. 1. The FeO₆ octahedra are slightly deformed with Fe—O distances varying from 1.8908 (8) to 2.1318 (8) Å and share a common edge with the highly distorted [(Zn2)₂O₈] dimer resulting from the edge-sharing of two triangular-based bipyramidal Zn2O₅ units. Sequences of these polyhedra build chains interconnected by PO₄ tetrahedra, forming a layer perpendicular to the b axis, as shown in Fig. 2. The remaining Zn1O₄ tetrahedra are linked to irregular PO₄ groups via common corners, forming tapes parallel to the c axis, which are linked together by Ca²⁺ cations in sheets perpendicular to the b axis (see Fig. 3). The obtained three-dimensional framework shows one type of channel running along the [001] direction in which the Ca²⁺ cations are located, each being coordinated by seven oxygen atoms (Fig. 4).

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

Figure 2
Edge-sharing triangular bipyramidal ZnO₅ units linked to FeO₆ octahedra and to PO₄ tetrahedra, forming a layer perpendicular to the b axis.

Figure 3
A layer perpendicular to the b axis, resulting from the chains connected via vertices of the ZnO₄ and PO₄ tetrahedra.

Figure 4
Polyhedral representation of CaZn₂Fe(PO₄)₃, showing the channels running along the [001] direction.

3. Database Survey

The formula of the title compound, CaZn₂Fe(PO₄)₃, is similar to some compounds with alluaudite structures, space group C2/c or the α-CrPO₄ structure, space group Imma. However, its structure is different and to our knowledge there is no known isotypic structure. Crystals of CaM₂Fe(PO₄)₃ (M = Mg, Co, Ni, Cu) compounds, which are predicted to have the same structures or isotypes are in preparation, while the structures of SrM₂Fe(PO₄)₃ (M = Co, Ni) compounds are isotypic with α-CrPO₄ (Bouraima et al., 2016 ; Ouaatta et al., 2015 ). Mention may also be made of other similar compounds, for example the phosphates Na₂Co₂Fe(PO₄)₃, NaCr₂Zn(PO₄)₃ and Na_1.66Zn_1.66Fe_1.34(PO₄)₃ (Bouraima et al., 2015 ; Souiwa et al., 2015 ; Khmiyas et al., 2015 ) adopting the alluaudite structure type. In conclusion, we can say that the structure of this phosphate is similar to the alluaudite structure but with lower symmetry.

4. Synthesis and crystallization

Single crystals of CaZn₂Fe(PO₄)₃ were synthesized by a conventional solid-state method. Appropriate amounts of metal nitrate reagents, in the presence of H₃PO₄ 85 wt%, were first dissolved in deionized water in the molar ratio Ca:Zn:Fe:P = 2:2:1:3 for 24 h. Then, the resulting solution was evaporated to dryness. The powder residue was ground in an agate mortar and progressively heated in a platinum crucible at a heating rate of 141 K h⁻¹ until melting occurred at 1283 K. The melted product was cooled down at a rate of 5 K h⁻¹. As result of the reaction, we obtained transparent crystals corresponding to the title compound CaZn₂Fe(PO₄)₃.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The reflections (202) and (330) probably affected by the beam-stop were omitted from the refinement. The maximum and minimum electron densities in the final Fourier map are at 0.56 and 0.44 Å from Ca1 and Zn2, respectively.

Table 1
Experimental details

Crystal data
Chemical formula	CaZn₂Fe(PO₄)₃
M_r	511.58
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	8.5619 (3), 15.2699 (5), 8.1190 (3)
β (°)	117.788 (2)
V (Å³)	939.06 (6)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	7.72
Crystal size (mm)	0.30 × 0.26 × 0.18

Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.600, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections	54053, 4985, 4493
R_int	0.033
(sin θ/λ)_max (Å⁻¹)	0.859

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.017, 0.041, 1.04
No. of reflections	4985
No. of parameters	172
Δρ_max, Δρ_min (e Å⁻³)	1.07, −0.78
Computer programs: APEX2 and SAINT (Bruker, 2009 ), SHELXT (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ), ORTEP-3 for Windows (Farrugia, 2012 ), DIAMOND (Brandenburg, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1497218

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989016012421/pj2033sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016012421/pj2033Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXT (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).

Calcium dizinc iron(III) tris(orthophosphate) top

Crystal data top

CaZn₂Fe(PO₄)₃	F(000) = 988
M_r = 511.58	D_x = 3.618 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.5619 (3) Å	Cell parameters from 4985 reflections
b = 15.2699 (5) Å	θ = 2.7–37.6°
c = 8.1190 (3) Å	µ = 7.72 mm⁻¹
β = 117.788 (2)°	T = 296 K
V = 939.06 (6) Å³	Block, black
Z = 4	0.30 × 0.26 × 0.18 mm

Data collection top

Bruker X8 APEX diffractometer	4985 independent reflections
Radiation source: fine-focus sealed tube	4493 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.033
φ and ω scans	θ_max = 37.6°, θ_min = 2.7°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −14→14
T_min = 0.600, T_max = 0.747	k = −26→26
54053 measured reflections	l = −10→13

Refinement top

Refinement on F²	172 parameters
Least-squares matrix: full	0 restraints
R[F² > 2σ(F²)] = 0.017	w = 1/[σ²(F_o²) + (0.0174P)² + 0.7655P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.041	(Δ/σ)_max = 0.003
S = 1.04	Δρ_max = 1.07 e Å⁻³
4985 reflections	Δρ_min = −0.78 e Å⁻³

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

	x	y	z	U_iso*/U_eq
Zn1	0.81685 (2)	0.73588 (2)	0.30142 (2)	0.00740 (3)
Zn2	0.88412 (2)	0.52265 (2)	0.59417 (2)	0.01026 (3)
Fe1	0.67075 (2)	0.49009 (2)	0.83003 (2)	0.00500 (3)
Ca1	0.27619 (3)	0.75762 (2)	0.47919 (3)	0.01070 (4)
P1	0.29665 (3)	0.58370 (2)	0.77261 (4)	0.00503 (4)
P2	0.96807 (3)	0.62244 (2)	0.09438 (4)	0.00499 (4)
P3	0.60325 (3)	0.64096 (2)	0.49014 (4)	0.00491 (4)
O1	0.29942 (13)	0.67932 (6)	0.72349 (13)	0.01271 (15)
O2	0.30273 (12)	0.58596 (6)	0.96463 (12)	0.01006 (14)
O3	0.12207 (10)	0.54161 (6)	0.62684 (12)	0.01114 (15)
O4	0.43948 (11)	0.52893 (6)	0.76475 (14)	0.01312 (16)
O5	0.77926 (10)	0.58832 (5)	0.00379 (12)	0.00895 (13)
O6	1.00136 (11)	0.67493 (6)	−0.04745 (13)	0.01045 (14)
O7	1.00262 (11)	0.68143 (6)	0.26134 (13)	0.01055 (14)
O8	1.09932 (10)	0.54481 (5)	0.17408 (12)	0.00724 (13)
O9	0.75426 (11)	0.65280 (6)	0.43941 (13)	0.01160 (15)
O10	0.59377 (10)	0.71947 (6)	0.60355 (12)	0.00974 (14)
O11	0.66602 (11)	0.55677 (5)	0.61102 (12)	0.00822 (13)
O12	0.41993 (10)	0.62799 (6)	0.32620 (12)	0.01012 (14)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Zn1	0.00645 (5)	0.00817 (5)	0.00801 (6)	0.00013 (4)	0.00374 (4)	0.00104 (4)
Zn2	0.00760 (5)	0.01471 (6)	0.01073 (6)	0.00042 (4)	0.00616 (4)	−0.00080 (5)
Fe1	0.00454 (5)	0.00602 (6)	0.00488 (6)	0.00044 (4)	0.00256 (4)	0.00061 (4)
Ca1	0.01029 (8)	0.01095 (9)	0.01178 (10)	0.00175 (6)	0.00591 (7)	0.00601 (7)
P1	0.00467 (9)	0.00607 (10)	0.00452 (10)	0.00011 (7)	0.00229 (8)	−0.00022 (8)
P2	0.00441 (9)	0.00482 (10)	0.00581 (11)	0.00038 (7)	0.00243 (8)	−0.00009 (8)
P3	0.00448 (9)	0.00500 (10)	0.00483 (10)	0.00004 (7)	0.00182 (8)	0.00031 (8)
O1	0.0222 (4)	0.0076 (3)	0.0109 (4)	−0.0001 (3)	0.0098 (3)	0.0019 (3)
O2	0.0169 (3)	0.0093 (3)	0.0063 (3)	0.0009 (3)	0.0073 (3)	0.0011 (3)
O3	0.0051 (3)	0.0176 (4)	0.0102 (4)	−0.0030 (3)	0.0030 (3)	−0.0063 (3)
O4	0.0065 (3)	0.0172 (4)	0.0157 (4)	0.0026 (3)	0.0052 (3)	−0.0045 (3)
O5	0.0056 (3)	0.0100 (3)	0.0101 (3)	−0.0016 (2)	0.0028 (2)	−0.0034 (3)
O6	0.0097 (3)	0.0107 (3)	0.0132 (4)	0.0029 (3)	0.0072 (3)	0.0061 (3)
O7	0.0079 (3)	0.0122 (3)	0.0115 (4)	−0.0005 (2)	0.0045 (3)	−0.0062 (3)
O8	0.0065 (3)	0.0073 (3)	0.0088 (3)	0.0026 (2)	0.0043 (2)	0.0020 (2)
O9	0.0111 (3)	0.0118 (3)	0.0161 (4)	0.0008 (3)	0.0098 (3)	0.0042 (3)
O10	0.0076 (3)	0.0091 (3)	0.0103 (3)	0.0006 (2)	0.0024 (3)	−0.0040 (3)
O11	0.0100 (3)	0.0080 (3)	0.0082 (3)	0.0028 (2)	0.0055 (3)	0.0039 (3)
O12	0.0068 (3)	0.0086 (3)	0.0097 (3)	−0.0002 (2)	−0.0006 (3)	−0.0020 (3)

Geometric parameters (Å, º) top

Zn1—O9	1.9266 (9)	Ca1—O2ⁱ	2.4075 (9)
Zn1—O7	1.9518 (8)	Ca1—O7^viii	2.4709 (9)
Zn1—O10ⁱ	1.9578 (8)	Ca1—O6^ix	2.4840 (9)
Zn1—O6ⁱⁱ	2.0120 (8)	Ca1—O10	2.4885 (8)
Zn2—O3ⁱⁱⁱ	1.9496 (8)	Ca1—O12	2.8984 (9)
Zn2—O11	2.0038 (8)	P1—O4	1.5073 (9)
Zn2—O3^iv	2.0241 (9)	P1—O1	1.5166 (9)
Zn2—O8^v	2.0911 (8)	P1—O2	1.5358 (9)
Zn2—O9	2.3371 (9)	P1—O3	1.5487 (8)
Fe1—O4	1.8908 (8)	P2—O5	1.5222 (8)
Fe1—O2^vi	1.9561 (9)	P2—O6	1.5348 (9)
Fe1—O5^vii	1.9700 (8)	P2—O7	1.5371 (9)
Fe1—O11	2.0330 (8)	P2—O8	1.5519 (8)
Fe1—O8^v	2.0547 (8)	P3—O12	1.5253 (8)
Fe1—O12^iv	2.1318 (8)	P3—O10	1.5365 (9)
Ca1—O1	2.2439 (9)	P3—O9	1.5396 (9)
Ca1—O1ⁱ	2.3795 (10)	P3—O11	1.5534 (8)

O9—Zn1—O7	106.60 (4)	O2ⁱ—Ca1—O6^ix	72.04 (3)
O9—Zn1—O10ⁱ	106.09 (4)	O7^viii—Ca1—O6^ix	65.76 (3)
O7—Zn1—O10ⁱ	124.80 (4)	O1—Ca1—O10	83.50 (3)
O9—Zn1—O6ⁱⁱ	116.31 (4)	O1ⁱ—Ca1—O10	85.92 (3)
O7—Zn1—O6ⁱⁱ	85.46 (3)	O2ⁱ—Ca1—O10	98.16 (3)
O10ⁱ—Zn1—O6ⁱⁱ	116.93 (4)	O7^viii—Ca1—O10	132.22 (3)
O3ⁱⁱⁱ—Zn2—O11	154.16 (4)	O6^ix—Ca1—O10	160.73 (3)
O3ⁱⁱⁱ—Zn2—O3^iv	77.67 (4)	O1—Ca1—O12	97.73 (3)
O11—Zn2—O3^iv	123.13 (3)	O1ⁱ—Ca1—O12	71.19 (3)
O3ⁱⁱⁱ—Zn2—O8^v	108.82 (4)	O2ⁱ—Ca1—O12	126.00 (3)
O11—Zn2—O8^v	75.00 (3)	O7^viii—Ca1—O12	79.74 (3)
O3^iv—Zn2—O8^v	121.44 (4)	O6^ix—Ca1—O12	145.10 (3)
O3ⁱⁱⁱ—Zn2—O9	98.73 (4)	O10—Ca1—O12	53.99 (3)
O11—Zn2—O9	65.84 (3)	O1—Ca1—O12ⁱⁱ	69.93 (3)
O3^iv—Zn2—O9	97.26 (4)	O1ⁱ—Ca1—O12ⁱⁱ	114.39 (3)
O8^v—Zn2—O9	135.92 (3)	O2ⁱ—Ca1—O12ⁱⁱ	57.96 (3)
O4—Fe1—O2^vi	96.63 (4)	O7^viii—Ca1—O12ⁱⁱ	140.52 (3)
O4—Fe1—O5^vii	92.55 (4)	O6^ix—Ca1—O12ⁱⁱ	78.49 (3)
O2^vi—Fe1—O5^vii	90.75 (4)	O10—Ca1—O12ⁱⁱ	82.24 (3)
O4—Fe1—O11	90.37 (4)	O12—Ca1—O12ⁱⁱ	135.98 (3)
O2^vi—Fe1—O11	171.82 (3)	O4—P1—O1	114.24 (6)
O5^vii—Fe1—O11	93.18 (4)	O4—P1—O2	114.28 (5)
O4—Fe1—O8^v	164.34 (4)	O1—P1—O2	104.36 (5)
O2^vi—Fe1—O8^v	97.38 (3)	O4—P1—O3	104.50 (5)
O5^vii—Fe1—O8^v	94.22 (3)	O1—P1—O3	109.05 (5)
O11—Fe1—O8^v	75.18 (3)	O2—P1—O3	110.42 (5)
O4—Fe1—O12^iv	93.16 (4)	O5—P2—O6	110.07 (5)
O2^vi—Fe1—O12^iv	82.55 (4)	O5—P2—O7	110.55 (5)
O5^vii—Fe1—O12^iv	171.65 (3)	O6—P2—O7	109.20 (5)
O11—Fe1—O12^iv	92.86 (4)	O5—P2—O8	109.84 (5)
O8^v—Fe1—O12^iv	81.77 (3)	O6—P2—O8	111.11 (5)
O1—Ca1—O1ⁱ	167.91 (4)	O7—P2—O8	106.00 (5)
O1—Ca1—O2ⁱ	126.91 (3)	O12—P3—O10	107.69 (5)
O1ⁱ—Ca1—O2ⁱ	60.49 (3)	O12—P3—O9	115.63 (5)
O1—Ca1—O7^viii	92.62 (3)	O10—P3—O9	110.75 (5)
O1ⁱ—Ca1—O7^viii	90.17 (3)	O12—P3—O11	110.86 (5)
O2ⁱ—Ca1—O7^viii	120.77 (3)	O10—P3—O11	111.50 (5)
O1—Ca1—O6^ix	89.31 (3)	O9—P3—O11	100.36 (5)
O1ⁱ—Ca1—O6^ix	102.55 (3)

Symmetry codes: (i) x, −y+3/2, z−1/2; (ii) x, −y+3/2, z+1/2; (iii) x+1, y, z; (iv) −x+1, −y+1, −z+1; (v) −x+2, −y+1, −z+1; (vi) −x+1, −y+1, −z+2; (vii) x, y, z+1; (viii) x−1, y, z; (ix) x−1, −y+3/2, 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 in Rabat, Morocco, for financial support.

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