The iron phosphate CaFe3(PO4)3O

Hidouri, M.; Ben Amara, M.

doi:10.1107/S160053680902827X

inorganic compounds

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ISSN: 2056-9890

Volume 65| Part 8| August 2009| Page i66

doi:10.1107/S160053680902827X

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The iron phosphate CaFe₃(PO₄)₃O

Mourad Hidouri ^a ^* and Mongi Ben Amara ^a

^aFaculté des Sciences de Monastir, 5019, Monastir, Tunisia.
^*Correspondence e-mail: mourad_hidouri@yahoo.fr

(Received 6 May 2009; accepted 17 July 2009; online 22 July 2009)

A new iron phosphate, calcium triiron(III) tris(phosphate) oxide, CaFe₃(PO₄)₃O, has been isolated and shown to exhibit a three-dimensional structure built by FeO₆ octahedra, FeO₅ trigonal bipyramids and PO₄ tetrahedra. The FeO_x (x = 5, 6) polyhedra are linked through common corners and edges, forming [Fe₆O₂₈]_∞ chains with branches running along [010]. Adjacent chains are connected by the phosphate groups via common corners and edges, giving rise to a three-dimensional framework analogous to those of the previously reported SrFe₃(PO₄)₃O and Bi_0.4Fe₃(PO₄)₃O structures, in which the Ca²⁺ cations occupy a single symmetry non-equivalent cavity.

Related literature

The interest in iron phosphates has increased following the discovery of LiFePO₄ with olivine-type structure, which is the most promising electrode material for Li-ion batteries, see: Padhi et al. (1997 ). The title compound is isostructural to the iron phosphates Bi_0.4Fe₃(PO₄)₃ (Benabad et al., 2000 ) and SrFe₃(PO₄)₃O (Morozov et al., 2003 ). For ionic radii, see: Shannon (1976 ). For P—O distances in orthophosphate groups, see: Baur (1974 ). For Ca—O distances in heptacoordinated Ca²⁺ ions in Ca₃(PO₄)₂, see: Mathew et al. (1977 ). For Fe—O distances for five-coordinated Fe³⁺ ions in NaCaFe₃(PO₄)₄, see: Hidouri et al. (2003 ).The valences of the cations were calculated using the Brown & Altermatt (1985 ) method.

Experimental

Crystal data

CaFe₃(PO₄)₃O
M_r = 508.54
Monoclinic, P 2₁ /m
a = 7.521 (2) Å
b = 6.330 (2) Å
c = 10.160 (2) Å
β = 100.03 (2)°
V = 476.3 (2) Å³
Z = 2
Mo Kα radiation
μ = 5.63 mm⁻¹
T = 293 K
0.36 × 0.22 × 0.22 mm

Data collection

Enraf–Nonius TurboCAD-4 diffractometer
Absorption correction: ψ scan (North et al., 1968 ) T_min = 0.193, T_max = 0.293
2072 measured reflections
1493 independent reflections
1412 reflections with I > 2σ(I)
R_int = 0.035
2 standard reflections frequency: 120 min intensity decay: 6.0%

Refinement

R[F² > 2σ(F²)] = 0.031
wR(F²) = 0.088
S = 1.12
1493 reflections
113 parameters
Δρ_max = 0.63 e Å⁻³
Δρ_min = −1.59 e Å⁻³

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994 ); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1998 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680902827X/er2067sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S160053680902827X/er2067Isup2.hkl

checkCIF report

Comment top

Iron phosphates are extensively studied for their rich structural chemistry owing to the possible occurrence of both +2 and +3 oxidation states for iron and the tendecy of its coordination polyhedra to form with the phosphate groups a variety of frameworks. Such adaptative crystal chemistry provides new and exciting aventures in the exploration of the intrinsic relationship between structure and composition. The interest in these materials is further accentuated since the discovery of LiFePO₄ with olivine-type structure the most promising electrode material for Li-ion batteries (Padhi et al., 1997).

As a part of a systematic exploration of the A₂O—MO—Fe₂O₃—P₂O₅ (A = alkali metal, M = divalent cation) in a search of new iron phosphates with interesting structures and subsequently intriguing properties, we describe here the structure of CaFe₃(PO₄)₃O, extracted from a mixture of nominal composition LiCaFe₃(PO₄)₄. This compound is isostructural to the previously reported iron phosphates Bi_0.4Fe₃(PO₄)₃ (Benabad et al., 2000) and SrFe₃(PO₄)₃O (Morozov et al., 2003). Its structure, shown in figure 1, is built from a three-dimensional arrangement based on two crystallographically distinct FeO₆ octahedra, one symmetry non equivalent FeO₅ polyhedron and three symmetry distinct PO₄ tetrahedra. The Fe polyhedra form [Fe₆O₂₈]_∞ chains with branches running along the [010] direction. In such chains (Fig. 2), each Fe(1)O₆ octahedron shares two opposite edges with two equivalent octahedra, one of the equatorial oxo-ligands forming each of the common edges being also shared with one Fe(2)O₆ octahedron. The latter is corner-linked with one one Fe(2)O₅ polyhedron to form the branches of the chain. The conntection of these chains is ensured by the phosphate tetrahedra in such a way that each PO₄ connects two adjacent chains either by sharing one edge with one chain and one corner with the other (P(1)O₄) or by sharing three corners with a same chain and the fourth with the other (P(2)O₄ and P(3)O₄). The three-dimensional framework constructed in this way delimits a single symmetry non equivalent cavity occupied by the Ca²⁺ cations.

The FeO₆ octahedra are both highly distorted as indicated by the Fe—O distances ranging from 1.986 (2) to 2.114 (2) Å for Fe(1)O₆ and from 1.870 (2) to 2.183 (3) Å for Fe(2)O₆ with average values of 2.037 (2) Å and 2.019 (3) Å, respectively, close to that 2.03 Å, predicted by Shannon for octahedral Fe³⁺ ions (Shannon, 1976). The FeO₅ polyhedron is also very distorted with Fe—O distances ranging from 1.872 (4) to 1.986 (2) Å. The mean distance of 1.940 (4) Å is consistent with those 1.946 Å and 1.956 Å, observed for five-coordinated Fe³⁺ ions in NaCaFe₃(PO₄)₄ (Hidouri et al., 2003). The PO₄ tetrahedra have P—O distances in the range 1.513 (3)–1.561 (3) Å with an overall distance of 1.535 (3) Å, close to that 1.537 calculated for the monophosphate groups (Baur, 1974). The Ca²⁺ cations occupy a single non equivalent site delimited by the Fe/P/O network. Its environement (Fig.3) is consisted by seven oxygen atoms with four Ca—O distances included between 2.391 (3) and 2.514 (2) Å showing the CaO₇ polyhedron to be highly distorted. The mean Ca—O distance of 2.462 (2) Å is in the range of those previously reported for heptacoordinated Ca²⁺ ions in Ca₃(PO₄)₂ (Mathew et al., 1977). The valences of all the cations were calculated using the Brown & Altermatt method (Brown & Altermatt, 1985). The calculated values of 1.85, 2.86, 3.10, 3.09, 4.94, 5.03 and 5.02 for Ca, Fe(1), Fe(2), Fe(3), P(1), P(2) and P(3), respectively are consistent with their respective oxidation numbers of 2.0, 3.0, 3.0, 3.0, 5.0, 5.0 and 5.0.

The structural similarity between the title compound and the iron phosphates SrFe₃(PO₄)₃O and Bi_0.4Fe₃(PO₄)₃O shows the great flexibility of the [Fe₃P₃O₁₃]_∞ framework which seems to accomodate various cations. Further invstigation of the chemical stablity of this structural type by including other cations would be of interest.

Related literature top

The interest iron phosphates has increased following the discovery of LiFePO₄ with olivine-type structure, which is the most promising electrode material for Li-ion batteries, see: Padhi et al. (1997). The title compound is isostructural to the iron phosphates Bi_0.4Fe₃(PO₄)₃ (Benabad et al., 2000) and SrFe₃(PO₄)₃O (Morozov et al., 2003). For ionic radii, see: Shannon (1976). For P—O distances in monophosphate groups, see: Baur (1974). For Ca—O distances in heptacoordinated Ca²⁺ ions in Ca₃(PO₄)₂, see: Mathew et al. (1977). For Fe—O distances for five-coordinated Fe³⁺ ions in NaCaFe₃(PO₄)₄, see: Hidouri et al. (2003). The valences of the cations were calculated using the Brown & Altermatt (1985) method.

Experimental top

Single crystals of the title compound were isolated during an attempt to crystallize LiCaFe₃(PO₄)₄ in a flux of lithium dimolybdate Li₂Mo₂O₇ in an atomic ratio, P: Mo = 8:1. Appropriate amounts of LiNO₃, CaCO₃, Fe(NO₃)₃.9H₂O, (NH₄)₂HPO₄ and MoO₃ were firstly dissolved in nitric acid and the solution obtained was dried for 24 h at 353 K. After grinding in an agate mortar to ensure its best homogeneity, the dry residue was heated in a platinum crucible to 673 K for 24 h in order to remove the decomposition products: NO₂, NH₃ and H₂O. The sample was then reground, melted at 1173 K for 1 h and subsequently cooled at a 10 °.h^-1 rate to 673 K after which the furnace was turned off. The final product was washed with warm water in order to dissolve the flux. From the mixture, dark brown and irregularely shaped crystals of CaFe₃(PO₄)₃O were extracted.

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top

	Fig. 1. : The CaFe₃(PO₄)₃O structure as projected along the [010] direction.
	Fig. 2. : A view of the [Fe₆O₂₈]_∞ chain running along the [010] direction.
	Fig. 3. : The environment of the Ca²⁺ cations showing the anisotropic atomic displacements.

calcium triiron(III) tris(phosphate) oxide top

Crystal data top

CaFe₃(PO₄)₃O	F(000) = 494
M_r = 508.54	D_x = 3.546 Mg m⁻³
Monoclinic, P2₁/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yb	Cell parameters from 25 reflections
a = 7.521 (2) Å	θ = 8.9–12.5°
b = 6.330 (2) Å	µ = 5.63 mm⁻¹
c = 10.160 (2) Å	T = 293 K
β = 100.03 (2)°	Prism, brown
V = 476.3 (2) Å³	0.36 × 0.22 × 0.22 mm
Z = 2

Data collection top

Enraf–Nonius TurboCAD-4 diffractometer	1412 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.035
Graphite monochromator	θ_max = 29.9°, θ_min = 2.0°
ω/2θ scans	h = −1→10
Absorption correction: ψ scan (North et al., 1968)	k = −1→8
T_min = 0.193, T_max = 0.293	l = −14→14
2072 measured reflections	2 standard reflections every 120 min
1493 independent reflections	intensity decay: 6.0%

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.031	w = 1/[σ²(F_o²) + (0.0585P)² + 0.6592P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.088	(Δ/σ)_max < 0.001
S = 1.12	Δρ_max = 0.63 e Å⁻³
1493 reflections	Δρ_min = −1.59 e Å⁻³
113 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.173 (7)

Crystal data top

CaFe₃(PO₄)₃O	V = 476.3 (2) Å³
M_r = 508.54	Z = 2
Monoclinic, P2₁/m	Mo Kα radiation
a = 7.521 (2) Å	µ = 5.63 mm⁻¹
b = 6.330 (2) Å	T = 293 K
c = 10.160 (2) Å	0.36 × 0.22 × 0.22 mm
β = 100.03 (2)°

Data collection top

Enraf–Nonius TurboCAD-4 diffractometer	1412 reflections with I > 2σ(I)
Absorption correction: ψ scan (North et al., 1968)	R_int = 0.035
T_min = 0.193, T_max = 0.293	2 standard reflections every 120 min
2072 measured reflections	intensity decay: 6.0%
1493 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.031	113 parameters
wR(F²) = 0.088	0 restraints
S = 1.12	Δρ_max = 0.63 e Å⁻³
1493 reflections	Δρ_min = −1.59 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. 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

	x	y	z	U_iso*/U_eq
Ca	0.66161 (10)	−0.2500	0.19595 (7)	0.00891 (18)
Fe1	0.0000	−0.5000	0.0000	0.00627 (16)
Fe2	−0.64926 (7)	−0.7500	0.20179 (5)	0.00561 (16)
Fe3	−0.21388 (7)	−0.7500	0.43643 (5)	0.00684 (16)
P1	−0.31703 (11)	−0.7500	0.11247 (8)	0.0052 (2)
O11	−0.5087 (3)	−0.7500	0.0310 (2)	0.0081 (5)
O12	−0.3598 (3)	−0.7500	0.2566 (3)	0.0080 (5)
O13	−0.2107 (2)	−0.5489 (3)	0.09386 (18)	0.0083 (3)
P2	0.26341 (12)	−0.2500	0.23940 (9)	0.0054 (2)
O21	0.0855 (3)	−0.2500	0.1340 (3)	0.0084 (5)
O22	0.2123 (4)	−0.2500	0.3770 (3)	0.0130 (5)
O23	0.3790 (2)	−0.4390 (3)	0.21363 (18)	0.0091 (3)
P3	0.21762 (12)	−0.7500	0.48890 (9)	0.0064 (2)
O31	0.0256 (4)	−0.7500	0.4084 (3)	0.0140 (5)
O32	0.3513 (4)	−0.7500	0.3933 (3)	0.0119 (5)
O33	−0.2479 (3)	−1.0599 (3)	0.41460 (18)	0.0116 (4)
O	−0.8765 (3)	−0.7500	0.0924 (2)	0.0070 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ca	0.0108 (3)	0.0090 (3)	0.0072 (3)	0.000	0.0024 (2)	0.000
Fe1	0.0075 (2)	0.0054 (2)	0.0068 (3)	−0.00023 (16)	0.00379 (17)	0.00011 (17)
Fe2	0.0066 (3)	0.0050 (3)	0.0057 (2)	0.000	0.00243 (17)	0.000
Fe3	0.0111 (3)	0.0060 (3)	0.0036 (3)	0.000	0.00167 (18)	0.000
P1	0.0065 (4)	0.0052 (4)	0.0045 (4)	0.000	0.0028 (3)	0.000
O11	0.0075 (11)	0.0106 (12)	0.0066 (11)	0.000	0.0019 (9)	0.000
O12	0.0096 (11)	0.0097 (12)	0.0058 (10)	0.000	0.0042 (8)	0.000
O13	0.0089 (7)	0.0075 (8)	0.0096 (8)	−0.0013 (6)	0.0048 (6)	0.0000 (6)
P2	0.0077 (4)	0.0049 (4)	0.0038 (4)	0.000	0.0019 (3)	0.000
O21	0.0099 (11)	0.0089 (11)	0.0065 (10)	0.000	0.0011 (9)	0.000
O22	0.0189 (13)	0.0164 (13)	0.0047 (11)	0.000	0.0050 (9)	0.000
O23	0.0106 (8)	0.0055 (7)	0.0114 (8)	0.0007 (6)	0.0028 (6)	−0.0005 (6)
P3	0.0103 (4)	0.0053 (4)	0.0044 (4)	0.000	0.0032 (3)	0.000
O31	0.0114 (12)	0.0208 (14)	0.0093 (12)	0.000	0.0005 (9)	0.000
O32	0.0135 (12)	0.0167 (13)	0.0070 (11)	0.000	0.0057 (9)	0.000
O33	0.0213 (9)	0.0059 (7)	0.0078 (8)	−0.0006 (7)	0.0031 (7)	0.0016 (6)
O	0.0065 (10)	0.0070 (11)	0.0068 (10)	0.000	−0.0005 (8)	0.000

Geometric parameters (Å, º) top

Ca—O11ⁱ	2.391 (3)	Fe3—O33	1.986 (2)
Ca—O13ⁱⁱ	2.434 (2)	Fe3—O33^xii	1.986 (2)
Ca—O13ⁱⁱⁱ	2.434 (2)	P1—O13	1.532 (2)
Ca—O23	2.473 (3)	P1—O13^xii	1.532 (2)
Ca—O23^iv	2.473 (3)	P1—O11	1.532 (3)
Ca—O33^v	2.514 (2)	P1—O12	1.554 (3)
Ca—O33^vi	2.514 (2)	P1—Ca^ix	3.2878 (10)
Ca—P2	3.102 (4)	P1—Ca^xiii	3.2878 (10)
Ca—P3^vii	3.1724 (16)	O11—Caⁱ	2.391 (3)
Ca—P1ⁱⁱ	3.2878 (10)	O13—Ca^ix	2.434 (2)
Ca—P1^v	3.2878 (10)	P2—O22	1.513 (3)
Fe1—O^viii	1.9860 (17)	P2—O23^iv	1.528 (2)
Fe1—Oⁱⁱ	1.9860 (17)	P2—O23	1.528 (2)
Fe1—O13	2.011 (2)	P2—O21	1.561 (3)
Fe1—O13ⁱ	2.011 (2)	O21—Fe1^xiv	2.1135 (18)
Fe1—O21ⁱ	2.1135 (18)	O22—Fe3^xi	1.894 (3)
Fe1—O21	2.1135 (18)	O23—Fe2ⁱⁱ	1.981 (2)
Fe2—O	1.870 (3)	P3—O32	1.515 (3)
Fe2—O32^ix	1.945 (3)	P3—O31	1.530 (3)
Fe2—O23^ix	1.981 (2)	P3—O33^xv	1.544 (2)
Fe2—O23^x	1.981 (2)	P3—O33^xvi	1.544 (2)
Fe2—O12	2.151 (4)	P3—Ca^vii	3.1724 (16)
Fe2—O11	2.183 (3)	O32—Fe2ⁱⁱ	1.945 (3)
Fe2—P1	2.803 (3)	O33—P3^xvi	1.544 (2)
Fe3—O31	1.872 (4)	O33—Ca^xiii	2.514 (2)
Fe3—O22^xi	1.894 (3)	O—Fe1^xvii	1.9860 (17)
Fe3—O12	1.960 (3)	O—Fe1^ix	1.9860 (17)

O11ⁱ—Ca—O13ⁱⁱ	75.42 (7)	O—Fe2—P1	125.58 (10)
O11ⁱ—Ca—O13ⁱⁱⁱ	75.42 (7)	O32^ix—Fe2—P1	118.50 (10)
O13ⁱⁱ—Ca—O13ⁱⁱⁱ	102.03 (10)	O23^ix—Fe2—P1	85.83 (5)
O11ⁱ—Ca—O23	78.17 (9)	O23^x—Fe2—P1	85.83 (5)
O13ⁱⁱ—Ca—O23	93.59 (8)	O31—Fe3—O22^xi	108.28 (14)
O13ⁱⁱⁱ—Ca—O23	144.58 (7)	O31—Fe3—O12	104.83 (13)
O11ⁱ—Ca—O23^iv	78.17 (9)	O22^xi—Fe3—O12	146.89 (12)
O13ⁱⁱ—Ca—O23^iv	144.58 (7)	O31—Fe3—O33	95.26 (6)
O13ⁱⁱⁱ—Ca—O23^iv	93.59 (8)	O22^xi—Fe3—O33	95.17 (6)
O23—Ca—O23^iv	57.88 (11)	O12—Fe3—O33	81.70 (6)
O11ⁱ—Ca—O33^v	149.65 (5)	O31—Fe3—O33^xii	95.26 (6)
O13ⁱⁱ—Ca—O33^v	133.04 (8)	O22^xi—Fe3—O33^xii	95.17 (6)
O13ⁱⁱⁱ—Ca—O33^v	86.46 (7)	O12—Fe3—O33^xii	81.70 (6)
O23—Ca—O33^v	105.74 (8)	O33—Fe3—O33^xii	162.15 (12)
O23^iv—Ca—O33^v	78.93 (9)	O13—P1—O13^xii	112.33 (16)
O11ⁱ—Ca—O33^vi	149.65 (5)	O13—P1—O11	113.29 (9)
O13ⁱⁱ—Ca—O33^vi	86.46 (7)	O13^xii—P1—O11	113.29 (9)
O13ⁱⁱⁱ—Ca—O33^vi	133.04 (8)	O13—P1—O12	108.34 (9)
O23—Ca—O33^vi	78.93 (9)	O13^xii—P1—O12	108.34 (9)
O23^iv—Ca—O33^vi	105.74 (8)	O11—P1—O12	100.34 (15)
O33^v—Ca—O33^vi	57.20 (9)	O13—P1—Fe2	123.62 (8)
O11ⁱ—Ca—P2	79.81 (9)	O13^xii—P1—Fe2	123.62 (8)
O13ⁱⁱ—Ca—P2	121.53 (5)	O11—P1—Fe2	50.73 (11)
O13ⁱⁱⁱ—Ca—P2	121.53 (5)	O12—P1—Fe2	49.61 (11)
O33^v—Ca—P2	89.64 (8)	O13—P1—Ca^ix	44.13 (8)
O33^vi—Ca—P2	89.64 (8)	O13^xii—P1—Ca^ix	151.82 (9)
O11ⁱ—Ca—P3^vii	168.11 (7)	O11—P1—Ca^ix	93.19 (4)
O13ⁱⁱ—Ca—P3^vii	111.42 (6)	O12—P1—Ca^ix	74.294 (19)
O13ⁱⁱⁱ—Ca—P3^vii	111.42 (6)	Fe2—P1—Ca^ix	80.22 (2)
O23—Ca—P3^vii	91.45 (7)	O13—P1—Ca^xiii	151.82 (9)
O23^iv—Ca—P3^vii	91.45 (7)	O13^xii—P1—Ca^xiii	44.13 (8)
P2—Ca—P3^vii	88.29 (7)	O11—P1—Ca^xiii	93.19 (4)
O11ⁱ—Ca—P1ⁱⁱ	77.77 (2)	O12—P1—Ca^xiii	74.294 (19)
O13ⁱⁱ—Ca—P1ⁱⁱ	25.99 (5)	Fe2—P1—Ca^xiii	80.22 (2)
O13ⁱⁱⁱ—Ca—P1ⁱⁱ	126.71 (6)	Ca^ix—P1—Ca^xiii	148.58 (4)
O23—Ca—P1ⁱⁱ	68.54 (6)	P1—O11—Fe2	96.36 (14)
O23^iv—Ca—P1ⁱⁱ	124.46 (6)	P1—O11—Caⁱ	140.38 (15)
O33^v—Ca—P1ⁱⁱ	132.14 (5)	Fe2—O11—Caⁱ	123.26 (13)
O33^vi—Ca—P1ⁱⁱ	75.48 (5)	P1—O12—Fe3	134.77 (17)
P2—Ca—P1ⁱⁱ	97.38 (2)	P1—O12—Fe2	97.02 (14)
P3^vii—Ca—P1ⁱⁱ	104.01 (2)	Fe3—O12—Fe2	128.22 (14)
O11ⁱ—Ca—P1^v	77.77 (2)	P1—O13—Fe1	131.13 (12)
O13ⁱⁱ—Ca—P1^v	126.71 (6)	P1—O13—Ca^ix	109.88 (10)
O23—Ca—P1^v	124.46 (6)	Fe1—O13—Ca^ix	118.97 (9)
O23^iv—Ca—P1^v	68.54 (6)	O22—P2—O23^iv	113.70 (10)
O33^v—Ca—P1^v	75.48 (5)	O22—P2—O23	113.70 (10)
O33^vi—Ca—P1^v	132.14 (5)	O23^iv—P2—O23	103.06 (16)
P2—Ca—P1^v	97.38 (2)	O22—P2—O21	107.95 (17)
P3^vii—Ca—P1^v	104.01 (2)	O23^iv—P2—O21	109.13 (10)
P1ⁱⁱ—Ca—P1^v	148.58 (4)	O23—P2—O21	109.13 (10)
O^viii—Fe1—Oⁱⁱ	180.0	O22—P2—Ca	122.57 (13)
O^viii—Fe1—O13	90.27 (10)	O23^iv—P2—Ca	51.94 (8)
Oⁱⁱ—Fe1—O13	89.73 (10)	O23—P2—Ca	51.94 (8)
O^viii—Fe1—O13ⁱ	89.73 (10)	O21—P2—Ca	129.47 (12)
Oⁱⁱ—Fe1—O13ⁱ	90.27 (10)	P2—O21—Fe1	124.75 (8)
O13—Fe1—O13ⁱ	180.0	P2—O21—Fe1^xiv	124.75 (8)
O^viii—Fe1—O21ⁱ	103.14 (9)	Fe1—O21—Fe1^xiv	96.97 (11)
Oⁱⁱ—Fe1—O21ⁱ	76.86 (9)	P2—O22—Fe3^xi	165.2 (2)
O13—Fe1—O21ⁱ	90.79 (9)	P2—O23—Fe2ⁱⁱ	136.88 (12)
O13ⁱ—Fe1—O21ⁱ	89.21 (9)	P2—O23—Ca	98.94 (11)
O^viii—Fe1—O21	76.86 (9)	Fe2ⁱⁱ—O23—Ca	124.12 (9)
Oⁱⁱ—Fe1—O21	103.14 (9)	O32—P3—O31	109.09 (17)
O13—Fe1—O21	89.21 (9)	O32—P3—O33^xv	111.49 (11)
O13ⁱ—Fe1—O21	90.79 (9)	O31—P3—O33^xv	111.12 (11)
O21ⁱ—Fe1—O21	180.0	O32—P3—O33^xvi	111.49 (11)
O—Fe2—O32^ix	115.92 (13)	O31—P3—O33^xvi	111.12 (11)
O—Fe2—O23^ix	96.52 (5)	O33^xv—P3—O33^xvi	102.43 (16)
O32^ix—Fe2—O23^ix	87.58 (6)	O32—P3—Ca^vii	122.83 (13)
O—Fe2—O23^x	96.52 (5)	O31—P3—Ca^vii	128.08 (12)
O32^ix—Fe2—O23^x	87.58 (6)	O33^xv—P3—Ca^vii	51.28 (8)
O23^ix—Fe2—O23^x	166.93 (11)	O33^xvi—P3—Ca^vii	51.28 (8)
O—Fe2—O12	158.95 (11)	P3—O31—Fe3	139.66 (19)
O32^ix—Fe2—O12	85.13 (12)	P3—O32—Fe2ⁱⁱ	139.08 (19)
O23^ix—Fe2—O12	83.75 (5)	P3^xvi—O33—Fe3	134.20 (12)
O23^x—Fe2—O12	83.75 (5)	P3^xvi—O33—Ca^xiii	100.10 (10)
O—Fe2—O11	92.67 (12)	Fe3—O33—Ca^xiii	125.55 (9)
O32^ix—Fe2—O11	151.41 (11)	Fe2—O—Fe1^xvii	125.79 (7)
O23^ix—Fe2—O11	89.23 (6)	Fe2—O—Fe1^ix	125.79 (7)
O23^x—Fe2—O11	89.23 (6)	Fe1^xvii—O—Fe1^ix	105.66 (12)
O12—Fe2—O11	66.28 (11)

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

Experimental details

Crystal data
Chemical formula	CaFe₃(PO₄)₃O
M_r	508.54
Crystal system, space group	Monoclinic, P2₁/m
Temperature (K)	293
a, b, c (Å)	7.521 (2), 6.330 (2), 10.160 (2)
β (°)	100.03 (2)
V (Å³)	476.3 (2)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	5.63
Crystal size (mm)	0.36 × 0.22 × 0.22

Data collection
Diffractometer	Enraf–Nonius TurboCAD-4 diffractometer
Absorption correction	ψ scan (North et al., 1968)
T_min, T_max	0.193, 0.293
No. of measured, independent and observed [I > 2σ(I)] reflections	2072, 1493, 1412
R_int	0.035
(sin θ/λ)_max (Å⁻¹)	0.702

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.031, 0.088, 1.12
No. of reflections	1493
No. of parameters	113
Δρ_max, Δρ_min (e Å⁻³)	0.63, −1.59

Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1994), XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1998), WinGX (Farrugia, 1999).

References

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