Crystal structure of calcium dinickel(II) iron(III) tris­­(orthophosphate): CaNi₂Fe(PO₄)₃

The title compound, CaNi₂Fe(PO₄)₃, was synthesized by solid-state reactions. Its structure is closely related to that of α-CrPO₄ in the space group Imma. Except for two O atoms in general positions, all atoms are located in special positions. The three-dimensional framework is built up from two types of sheets extending parallel to (100). The first sheet is made up from two edge-sharing [NiO₆] octa­hedra, leading to the formation of [Ni₂O₁₀] double octa­hedra that are connected to two PO₄ tetra­hedra through a common edge and corners. The second sheet results from rows of corner-sharing [FeO₆] octa­hedra and PO₄ tetra­hedra forming an infinite linear chain. These layers are linked together through common corners of PO₄ tetra­hedra and [FeO₆] octa­hedra, resulting in an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] in which the eightfold-coordinated Ca^II cations are located.

1. Chemical context

Phosphates belonging to the alluaudite (Moore, 1971) or to the α-CrPO₄ (Attfield et al., 1988) structure type exhibit inter­esting physical and chemical properties. Consequently, these compounds have many promising applications such as use as positive electrodes in lithium and sodium batteries (Kim et al., 2014; Huang et al., 2015) or as catalysts (Kacimi et al., 2005). Over the last few years, phosphate-based compounds crystallizing in the α-CrPO₄ or alluaudite structure types have been investigated by us. In this context, new phosphates adopting the alluaudite or α-CrPO₄ structure type have been synthesized and structurally characterized. For example, the mixed-valence manganese phosphates PbMn^II₂Mn^III(PO₄)₃ (Alhakmi et al., 2013) and PbMn^II₂Mn^III(PO₄)₃ (Assani et al., 2013), the magnesium phosphate NaMg₃(PO₄)(HPO₄)₂ (Ould Saleck et al., 2015) and silver nickel phosphate Ag₂Ni₃(HPO₄)(PO₄)₂ (Assani et al., 2011) were synthesized by hydro­thermal methods, while solid-state reactions were applied to synthesize SrNi₂Fe(PO₄)₃ (Ouaatta et al., 2015) and Na₂Co₂Fe(PO₄)₃ (Bouraima et al., 2015). In a continuation of the latter preparation route, we have investigated pseudo-quaternary systems MO–NiO–Fe₂O₃–P₂O₅ (M represents a divalent cation) and report here on the synthesis and crystal structure of the title compound, CaNi₂Fe(PO₄)₃.

2. Structural commentary

CaNi₂Fe(PO₄)₃ crystallizes in the α-CrPO₄ structure type. The principal building units of the crystal structure are one [CaO₈] polyhedron, [FeO₆] and [NiO₆] octa­hedra and PO₄ tetra­hedra, as shown in Fig. 1.The octa­hedral coordination sphere of the iron(III) cation is more distorted than that of nickel(II), with Fe—O bond lengths in the range 1.9504 (7)–2.0822 (11) Å and Ni—O bond lengths in the range 2.0498 (8)–2.0841 (8) Å. In the title structure, all atoms are on special positions, except for the two oxygen atoms O1 and O2, which are on general positions. The structure can be described by the stacking of two types of sheets extending parallel to (100). The first sheet is formed by alternating [FeO₆] octa­hedra and PO₄ tetra­hedra sharing corners to build a linear infinite chain surrounding a zigzag chain of Ca^II+ cations (Fig. 2). The second sheet is built up from two edge-sharing [NiO₆] octa­hedra leading to the formation of [Ni₂O₁₀] double octa­hedra, which are connected to two PO₄ tetra­hedra by a common edge and a common corner, as shown in Fig. 3. The linkage of both layers, through vertices of PO₄ tetra­hedra and [FeO₆] octa­hedra, gives rise to the formation of an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] in which the Ca^II cations are located with eight neighbouring O atoms, as shown in Fig. 4. The title compound has a stoichiometric composition like that of the related strontium homologue SrNi₂Fe(PO₄)₃.

Figure 1 The principal building units in the crystal structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) −x + 2, −y + , z + 1; (ii) x, y, z + 1; (iii) −x + 2, −y + , z; (iv) −x + , −y + 1, z + ; (v) x + , y + , z + ; (vi) −x + , y + , z + ; (vii) x + , −y + 1, z + ; (viii) −x + , −y + , −z + ; (ix) −x + , y, −z + ; (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 − , y, −z + .]

Figure 2 A chain formed by sharing corners of PO4 tetra­hedra and [FeO6] octa­hedra, alternating with a zigzag chain of calcium cations.

Figure 3 Edge-sharing [NiO6] octa­hedra linked by PO4 tetra­hedra, forming a sheet parallel to (100).

Figure 4 Polyhedral representation of CaNiO2Fe(PO4)3, showing channels running parallel to [100].

3. Synthesis and crystallization

CaNi₂Fe(PO₄)₃ was prepared by solid-state reactions in air. Stoichiometric mixtures of calcium, nickel and iron precursors were dissolved in water to which 85%_wt phospho­ric acid was added. The obtained mixture was stirred without heating for 24 h and was subsequently evaporated to dryness at 343 K. The resulting dry residue was ground in an agate mortar until homogeneity, progressively heated in a platinum crucible up to 873 K to remove the volatile decomposition products, and then melted at 1433 K. The molten product was cooled down slowly with a 5 K h⁻¹ rate and then to room temperature. The crystals obtained after washing with water were orange with parallelepipedal forms.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The maximum and minimum remaining electron densities are 0.68 and 0.41 Å, respectively, away from the Ni1 site.

Table 1
Experimental details

Crystal data
Chemical formula	CaNi2Fe(PO4)3
Mr	498.26
Crystal system, space group	Orthorhombic, Imma
Temperature (K)	296
a, b, c (Å)	10.3126 (3), 13.1138 (3), 6.4405 (2)
V (Å^3)	871.00 (4)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	7.14
Crystal size (mm)	0.30 × 0.27 × 0.21
Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.596, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	8446, 1171, 1153
Rint	0.020
(sin θ/λ)max (Å^−1)	0.840
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.017, 0.044, 1.17
No. of reflections	1171
No. of parameters	54
Δρmax, Δρmin (e Å^−3)	0.76, −0.63
Computer programs: APEX2 and SAINT (Bruker, 2009), SHELXT2014 (Sheldrick, 2015a), SHELXL2014 (Sheldrick, 2015b), ORTEP-3 for Windows (Farrugia, 2012), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010).

Supporting information

Computing details

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).

Calcium dinickel(II) iron(III) tris(orthophosphate)

Crystal data

CaNi2Fe(PO4)3	Dx = 3.800 Mg m^−3
Mr = 498.26	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Imma	Cell parameters from 1171 reflections
a = 10.3126 (3) Å	θ = 3.1–36.6°
b = 13.1138 (3) Å	µ = 7.14 mm^−1
c = 6.4405 (2) Å	T = 296 K
V = 871.00 (4) Å^3	Parallelepiped, orange
Z = 4	0.30 × 0.27 × 0.21 mm
F(000) = 972

Data collection

Bruker X8 APEX diffractometer	1171 independent reflections
Radiation source: fine-focus sealed tube	1153 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
φ and ω scans	θmax = 36.6°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −16→17
Tmin = 0.596, Tmax = 0.748	k = −20→22
8446 measured reflections	l = −10→10

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0216P)^2 + 1.467P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.017	(Δ/σ)max = 0.001
wR(F^2) = 0.044	Δρmax = 0.76 e Å^−3
S = 1.17	Δρmin = −0.63 e Å^−3
1171 reflections	Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
54 parameters	Extinction coefficient: 0.0033 (2)

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ni1	0.7500	0.36655 (2)	0.7500	0.00475 (5)
Fe1	0.5000	0.0000	0.5000	0.00372 (6)
Ca1	0.5000	0.2500	0.08981 (7)	0.01187 (8)
P1	0.7500	0.57298 (3)	0.7500	0.00385 (7)
P2	0.5000	0.2500	0.58291 (8)	0.00327 (8)
O1	0.86146 (7)	0.49415 (6)	0.79418 (13)	0.00590 (12)
O4	0.61754 (11)	0.2500	0.73284 (17)	0.00587 (16)
O3	0.5000	0.15625 (8)	0.44256 (18)	0.00672 (17)
O2	0.70724 (8)	0.63786 (6)	0.93385 (12)	0.00762 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.00486 (9)	0.00326 (8)	0.00613 (9)	0.000	−0.00056 (5)	0.000
Fe1	0.00264 (10)	0.00397 (11)	0.00455 (11)	0.000	0.000	−0.00016 (8)
Ca1	0.01508 (18)	0.01319 (18)	0.00735 (16)	0.000	0.000	0.000
P1	0.00450 (14)	0.00307 (14)	0.00398 (14)	0.000	−0.00041 (9)	0.000
P2	0.00320 (17)	0.00246 (17)	0.00414 (18)	0.000	0.000	0.000
O1	0.0045 (3)	0.0054 (3)	0.0079 (3)	0.0006 (2)	−0.0021 (2)	−0.0004 (2)
O4	0.0049 (4)	0.0057 (4)	0.0070 (4)	0.000	−0.0023 (3)	0.000
O3	0.0082 (4)	0.0045 (4)	0.0075 (4)	0.000	0.000	−0.0024 (3)
O2	0.0102 (3)	0.0069 (3)	0.0057 (3)	0.0018 (2)	0.0001 (2)	−0.0020 (2)

Geometric parameters (Å, º)

Ni1—O1	2.0498 (8)	Ca1—O2^xi	2.5987 (8)
Ni1—O1^i	2.0499 (8)	Ca1—O2^xii	2.5987 (8)
Ni1—O4	2.0529 (8)	Ca1—O2^xiii	2.5987 (8)
Ni1—O4^ii	2.0529 (8)	Ca1—O4^xiv	2.5990 (12)
Ni1—O2^iii	2.0841 (8)	Ca1—O4^xv	2.5990 (12)
Ni1—O2^iv	2.0841 (8)	Ca1—P2	3.1758 (7)
Fe1—O1^ii	1.9504 (7)	Ca1—P2^xv	3.2647 (7)
Fe1—O1^v	1.9504 (7)	P1—O2^i	1.5233 (8)
Fe1—O1^vi	1.9504 (7)	P1—O2	1.5233 (8)
Fe1—O1^vii	1.9504 (7)	P1—O1^i	1.5719 (8)
Fe1—O3^viii	2.0822 (11)	P1—O1	1.5719 (8)
Fe1—O3	2.0822 (11)	P2—O3	1.5259 (11)
Ca1—O3	2.5832 (12)	P2—O3^ix	1.5259 (11)
Ca1—O3^ix	2.5832 (12)	P2—O4^ix	1.5498 (11)
Ca1—O2^x	2.5987 (8)	P2—O4	1.5498 (11)
O1—Ni1—O1^i	70.58 (4)	O2^x—Ca1—O2^xi	173.27 (4)
O1—Ni1—O4	171.24 (3)	O3—Ca1—O2^xii	77.42 (2)
O1^i—Ni1—O4	103.13 (3)	O3^ix—Ca1—O2^xii	108.72 (2)
O1—Ni1—O4^ii	103.13 (3)	O2^x—Ca1—O2^xii	110.65 (3)
O1^i—Ni1—O4^ii	171.24 (3)	O2^xi—Ca1—O2^xii	68.92 (3)
O4—Ni1—O4^ii	83.76 (5)	O3—Ca1—O2^xiii	108.72 (2)
O1—Ni1—O2^iii	90.33 (3)	O3^ix—Ca1—O2^xiii	77.42 (2)
O1^i—Ni1—O2^iii	92.27 (3)	O2^x—Ca1—O2^xiii	68.92 (3)
O4—Ni1—O2^iii	83.75 (4)	O2^xi—Ca1—O2^xiii	110.65 (3)
O4^ii—Ni1—O2^iii	93.87 (4)	O2^xii—Ca1—O2^xiii	173.27 (4)
O1—Ni1—O2^iv	92.27 (3)	O3—Ca1—O4^xiv	141.08 (2)
O1^i—Ni1—O2^iv	90.33 (3)	O3^ix—Ca1—O4^xiv	141.08 (2)
O4—Ni1—O2^iv	93.87 (4)	O2^x—Ca1—O4^xiv	64.19 (3)
O4^ii—Ni1—O2^iv	83.75 (4)	O2^xi—Ca1—O4^xiv	109.37 (3)
O2^iii—Ni1—O2^iv	176.81 (4)	O2^xii—Ca1—O4^xiv	109.37 (3)
O1^ii—Fe1—O1^v	180.0	O2^xiii—Ca1—O4^xiv	64.19 (3)
O1^ii—Fe1—O1^vi	85.81 (5)	O3—Ca1—O4^xv	141.08 (2)
O1^v—Fe1—O1^vi	94.19 (5)	O3^ix—Ca1—O4^xv	141.08 (2)
O1^ii—Fe1—O1^vii	94.19 (5)	O2^x—Ca1—O4^xv	109.37 (3)
O1^v—Fe1—O1^vii	85.81 (5)	O2^xi—Ca1—O4^xv	64.19 (3)
O1^vi—Fe1—O1^vii	180.0	O2^xii—Ca1—O4^xv	64.19 (3)
O1^ii—Fe1—O3^viii	85.29 (3)	O2^xiii—Ca1—O4^xv	109.37 (3)
O1^v—Fe1—O3^viii	94.71 (3)	O4^xiv—Ca1—O4^xv	55.60 (5)
O1^vi—Fe1—O3^viii	94.71 (3)	O2^i—P1—O2	112.08 (6)
O1^vii—Fe1—O3^viii	85.29 (3)	O2^i—P1—O1^i	116.00 (4)
O1^ii—Fe1—O3	94.71 (3)	O2—P1—O1^i	107.24 (4)
O1^v—Fe1—O3	85.29 (3)	O2^i—P1—O1	107.24 (4)
O1^vi—Fe1—O3	85.29 (3)	O2—P1—O1	116.00 (4)
O1^vii—Fe1—O3	94.71 (3)	O1^i—P1—O1	97.76 (6)
O3^viii—Fe1—O3	180.000 (10)	O3—P2—O3^ix	107.35 (9)
O3—Ca1—O3^ix	56.84 (5)	O3—P2—O4^ix	111.66 (3)
O3—Ca1—O2^x	77.42 (2)	O3^ix—P2—O4^ix	111.66 (3)
O3^ix—Ca1—O2^x	108.72 (2)	O3—P2—O4	111.66 (3)
O3—Ca1—O2^xi	108.72 (2)	O3^ix—P2—O4	111.66 (3)
O3^ix—Ca1—O2^xi	77.42 (2)	O4^ix—P2—O4	102.91 (9)

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