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Acta Crystallogr Sect E Struct Rep Online. 2009 August 1; 65(Pt 8): i66.
Published online 2009 July 22. doi:  10.1107/S160053680902827X
PMCID: PMC2977148

The iron phosphate CaFe3(PO4)3O

Abstract

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 FeOx (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 Bi0.4Fe3(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 [triangle]). The title compound is isostructural to the iron phosphates Bi0.4Fe3(PO4)3 (Benabad et al., 2000 [triangle]) and SrFe3(PO4)3O (Morozov et al., 2003 [triangle]). For ionic radii, see: Shannon (1976 [triangle]). For P—O distances in orthophosphate groups, see: Baur (1974 [triangle]). For Ca—O distances in heptacoordinated Ca2+ ions in Ca3(PO4)2, see: Mathew et al. (1977 [triangle]). For Fe—O distances for five-coordinated Fe3+ ions in NaCaFe3(PO4)4, see: Hidouri et al. (2003 [triangle]).The valences of the cations were calculated using the Brown & Altermatt (1985 [triangle]) method.

Experimental

Crystal data

  • CaFe3(PO4)3O
  • M r = 508.54
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-00i66-efi1.jpg
  • 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 [triangle]) 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[F 2 > 2σ(F 2)] = 0.031
  • wR(F 2) = 0.088
  • S = 1.12
  • 1493 reflections
  • 113 parameters
  • Δρmax = 0.63 e Å−3
  • Δρmin = −1.59 e Å−3

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

Supplementary Material

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

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

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Comment

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 Bi0.4Fe3(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 Bi0.4Fe3(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.

Experimental

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.

Refinement

The Fe and Ca atoms were loctaed by direct methods and the remaining atoms were found by successive difference Fourier maps. All atomic positions were refined with anisotrop displacement parameterers.

Figures

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.

Crystal data

CaFe3(PO4)3OF(000) = 494
Mr = 508.54Dx = 3.546 Mg m3
Monoclinic, P21/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybCell parameters from 25 reflections
a = 7.521 (2) Åθ = 8.9–12.5°
b = 6.330 (2) ŵ = 5.63 mm1
c = 10.160 (2) ÅT = 293 K
β = 100.03 (2)°Prism, brown
V = 476.3 (2) Å30.36 × 0.22 × 0.22 mm
Z = 2

Data collection

Enraf–Nonius TurboCAD-4 diffractometer1412 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.035
graphiteθmax = 29.9°, θmin = 2.0°
ω/2θ scansh = −1→10
Absorption correction: ψ scan (North et al., 1968)k = −1→8
Tmin = 0.193, Tmax = 0.293l = −14→14
2072 measured reflections2 standard reflections every 120 min
1493 independent reflections intensity decay: 6.0%

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.031w = 1/[σ2(Fo2) + (0.0585P)2 + 0.6592P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.088(Δ/σ)max < 0.001
S = 1.12Δρmax = 0.63 e Å3
1493 reflectionsΔρmin = −1.59 e Å3
113 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.173 (7)

Special details

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)

xyzUiso*/Ueq
Ca0.66161 (10)−0.25000.19595 (7)0.00891 (18)
Fe10.0000−0.50000.00000.00627 (16)
Fe2−0.64926 (7)−0.75000.20179 (5)0.00561 (16)
Fe3−0.21388 (7)−0.75000.43643 (5)0.00684 (16)
P1−0.31703 (11)−0.75000.11247 (8)0.0052 (2)
O11−0.5087 (3)−0.75000.0310 (2)0.0081 (5)
O12−0.3598 (3)−0.75000.2566 (3)0.0080 (5)
O13−0.2107 (2)−0.5489 (3)0.09386 (18)0.0083 (3)
P20.26341 (12)−0.25000.23940 (9)0.0054 (2)
O210.0855 (3)−0.25000.1340 (3)0.0084 (5)
O220.2123 (4)−0.25000.3770 (3)0.0130 (5)
O230.3790 (2)−0.4390 (3)0.21363 (18)0.0091 (3)
P30.21762 (12)−0.75000.48890 (9)0.0064 (2)
O310.0256 (4)−0.75000.4084 (3)0.0140 (5)
O320.3513 (4)−0.75000.3933 (3)0.0119 (5)
O33−0.2479 (3)−1.0599 (3)0.41460 (18)0.0116 (4)
O−0.8765 (3)−0.75000.0924 (2)0.0070 (5)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Ca0.0108 (3)0.0090 (3)0.0072 (3)0.0000.0024 (2)0.000
Fe10.0075 (2)0.0054 (2)0.0068 (3)−0.00023 (16)0.00379 (17)0.00011 (17)
Fe20.0066 (3)0.0050 (3)0.0057 (2)0.0000.00243 (17)0.000
Fe30.0111 (3)0.0060 (3)0.0036 (3)0.0000.00167 (18)0.000
P10.0065 (4)0.0052 (4)0.0045 (4)0.0000.0028 (3)0.000
O110.0075 (11)0.0106 (12)0.0066 (11)0.0000.0019 (9)0.000
O120.0096 (11)0.0097 (12)0.0058 (10)0.0000.0042 (8)0.000
O130.0089 (7)0.0075 (8)0.0096 (8)−0.0013 (6)0.0048 (6)0.0000 (6)
P20.0077 (4)0.0049 (4)0.0038 (4)0.0000.0019 (3)0.000
O210.0099 (11)0.0089 (11)0.0065 (10)0.0000.0011 (9)0.000
O220.0189 (13)0.0164 (13)0.0047 (11)0.0000.0050 (9)0.000
O230.0106 (8)0.0055 (7)0.0114 (8)0.0007 (6)0.0028 (6)−0.0005 (6)
P30.0103 (4)0.0053 (4)0.0044 (4)0.0000.0032 (3)0.000
O310.0114 (12)0.0208 (14)0.0093 (12)0.0000.0005 (9)0.000
O320.0135 (12)0.0167 (13)0.0070 (11)0.0000.0057 (9)0.000
O330.0213 (9)0.0059 (7)0.0078 (8)−0.0006 (7)0.0031 (7)0.0016 (6)
O0.0065 (10)0.0070 (11)0.0068 (10)0.000−0.0005 (8)0.000

Geometric parameters (Å, °)

Ca—O11i2.391 (3)Fe3—O331.986 (2)
Ca—O13ii2.434 (2)Fe3—O33xii1.986 (2)
Ca—O13iii2.434 (2)P1—O131.532 (2)
Ca—O232.473 (3)P1—O13xii1.532 (2)
Ca—O23iv2.473 (3)P1—O111.532 (3)
Ca—O33v2.514 (2)P1—O121.554 (3)
Ca—O33vi2.514 (2)P1—Caix3.2878 (10)
Ca—P23.102 (4)P1—Caxiii3.2878 (10)
Ca—P3vii3.1724 (16)O11—Cai2.391 (3)
Ca—P1ii3.2878 (10)O13—Caix2.434 (2)
Ca—P1v3.2878 (10)P2—O221.513 (3)
Fe1—Oviii1.9860 (17)P2—O23iv1.528 (2)
Fe1—Oii1.9860 (17)P2—O231.528 (2)
Fe1—O132.011 (2)P2—O211.561 (3)
Fe1—O13i2.011 (2)O21—Fe1xiv2.1135 (18)
Fe1—O21i2.1135 (18)O22—Fe3xi1.894 (3)
Fe1—O212.1135 (18)O23—Fe2ii1.981 (2)
Fe2—O1.870 (3)P3—O321.515 (3)
Fe2—O32ix1.945 (3)P3—O311.530 (3)
Fe2—O23ix1.981 (2)P3—O33xv1.544 (2)
Fe2—O23x1.981 (2)P3—O33xvi1.544 (2)
Fe2—O122.151 (4)P3—Cavii3.1724 (16)
Fe2—O112.183 (3)O32—Fe2ii1.945 (3)
Fe2—P12.803 (3)O33—P3xvi1.544 (2)
Fe3—O311.872 (4)O33—Caxiii2.514 (2)
Fe3—O22xi1.894 (3)O—Fe1xvii1.9860 (17)
Fe3—O121.960 (3)O—Fe1ix1.9860 (17)
O11i—Ca—O13ii75.42 (7)O—Fe2—P1125.58 (10)
O11i—Ca—O13iii75.42 (7)O32ix—Fe2—P1118.50 (10)
O13ii—Ca—O13iii102.03 (10)O23ix—Fe2—P185.83 (5)
O11i—Ca—O2378.17 (9)O23x—Fe2—P185.83 (5)
O13ii—Ca—O2393.59 (8)O31—Fe3—O22xi108.28 (14)
O13iii—Ca—O23144.58 (7)O31—Fe3—O12104.83 (13)
O11i—Ca—O23iv78.17 (9)O22xi—Fe3—O12146.89 (12)
O13ii—Ca—O23iv144.58 (7)O31—Fe3—O3395.26 (6)
O13iii—Ca—O23iv93.59 (8)O22xi—Fe3—O3395.17 (6)
O23—Ca—O23iv57.88 (11)O12—Fe3—O3381.70 (6)
O11i—Ca—O33v149.65 (5)O31—Fe3—O33xii95.26 (6)
O13ii—Ca—O33v133.04 (8)O22xi—Fe3—O33xii95.17 (6)
O13iii—Ca—O33v86.46 (7)O12—Fe3—O33xii81.70 (6)
O23—Ca—O33v105.74 (8)O33—Fe3—O33xii162.15 (12)
O23iv—Ca—O33v78.93 (9)O13—P1—O13xii112.33 (16)
O11i—Ca—O33vi149.65 (5)O13—P1—O11113.29 (9)
O13ii—Ca—O33vi86.46 (7)O13xii—P1—O11113.29 (9)
O13iii—Ca—O33vi133.04 (8)O13—P1—O12108.34 (9)
O23—Ca—O33vi78.93 (9)O13xii—P1—O12108.34 (9)
O23iv—Ca—O33vi105.74 (8)O11—P1—O12100.34 (15)
O33v—Ca—O33vi57.20 (9)O13—P1—Fe2123.62 (8)
O11i—Ca—P279.81 (9)O13xii—P1—Fe2123.62 (8)
O13ii—Ca—P2121.53 (5)O11—P1—Fe250.73 (11)
O13iii—Ca—P2121.53 (5)O12—P1—Fe249.61 (11)
O33v—Ca—P289.64 (8)O13—P1—Caix44.13 (8)
O33vi—Ca—P289.64 (8)O13xii—P1—Caix151.82 (9)
O11i—Ca—P3vii168.11 (7)O11—P1—Caix93.19 (4)
O13ii—Ca—P3vii111.42 (6)O12—P1—Caix74.294 (19)
O13iii—Ca—P3vii111.42 (6)Fe2—P1—Caix80.22 (2)
O23—Ca—P3vii91.45 (7)O13—P1—Caxiii151.82 (9)
O23iv—Ca—P3vii91.45 (7)O13xii—P1—Caxiii44.13 (8)
P2—Ca—P3vii88.29 (7)O11—P1—Caxiii93.19 (4)
O11i—Ca—P1ii77.77 (2)O12—P1—Caxiii74.294 (19)
O13ii—Ca—P1ii25.99 (5)Fe2—P1—Caxiii80.22 (2)
O13iii—Ca—P1ii126.71 (6)Caix—P1—Caxiii148.58 (4)
O23—Ca—P1ii68.54 (6)P1—O11—Fe296.36 (14)
O23iv—Ca—P1ii124.46 (6)P1—O11—Cai140.38 (15)
O33v—Ca—P1ii132.14 (5)Fe2—O11—Cai123.26 (13)
O33vi—Ca—P1ii75.48 (5)P1—O12—Fe3134.77 (17)
P2—Ca—P1ii97.38 (2)P1—O12—Fe297.02 (14)
P3vii—Ca—P1ii104.01 (2)Fe3—O12—Fe2128.22 (14)
O11i—Ca—P1v77.77 (2)P1—O13—Fe1131.13 (12)
O13ii—Ca—P1v126.71 (6)P1—O13—Caix109.88 (10)
O23—Ca—P1v124.46 (6)Fe1—O13—Caix118.97 (9)
O23iv—Ca—P1v68.54 (6)O22—P2—O23iv113.70 (10)
O33v—Ca—P1v75.48 (5)O22—P2—O23113.70 (10)
O33vi—Ca—P1v132.14 (5)O23iv—P2—O23103.06 (16)
P2—Ca—P1v97.38 (2)O22—P2—O21107.95 (17)
P3vii—Ca—P1v104.01 (2)O23iv—P2—O21109.13 (10)
P1ii—Ca—P1v148.58 (4)O23—P2—O21109.13 (10)
Oviii—Fe1—Oii180.0O22—P2—Ca122.57 (13)
Oviii—Fe1—O1390.27 (10)O23iv—P2—Ca51.94 (8)
Oii—Fe1—O1389.73 (10)O23—P2—Ca51.94 (8)
Oviii—Fe1—O13i89.73 (10)O21—P2—Ca129.47 (12)
Oii—Fe1—O13i90.27 (10)P2—O21—Fe1124.75 (8)
O13—Fe1—O13i180.0P2—O21—Fe1xiv124.75 (8)
Oviii—Fe1—O21i103.14 (9)Fe1—O21—Fe1xiv96.97 (11)
Oii—Fe1—O21i76.86 (9)P2—O22—Fe3xi165.2 (2)
O13—Fe1—O21i90.79 (9)P2—O23—Fe2ii136.88 (12)
O13i—Fe1—O21i89.21 (9)P2—O23—Ca98.94 (11)
Oviii—Fe1—O2176.86 (9)Fe2ii—O23—Ca124.12 (9)
Oii—Fe1—O21103.14 (9)O32—P3—O31109.09 (17)
O13—Fe1—O2189.21 (9)O32—P3—O33xv111.49 (11)
O13i—Fe1—O2190.79 (9)O31—P3—O33xv111.12 (11)
O21i—Fe1—O21180.0O32—P3—O33xvi111.49 (11)
O—Fe2—O32ix115.92 (13)O31—P3—O33xvi111.12 (11)
O—Fe2—O23ix96.52 (5)O33xv—P3—O33xvi102.43 (16)
O32ix—Fe2—O23ix87.58 (6)O32—P3—Cavii122.83 (13)
O—Fe2—O23x96.52 (5)O31—P3—Cavii128.08 (12)
O32ix—Fe2—O23x87.58 (6)O33xv—P3—Cavii51.28 (8)
O23ix—Fe2—O23x166.93 (11)O33xvi—P3—Cavii51.28 (8)
O—Fe2—O12158.95 (11)P3—O31—Fe3139.66 (19)
O32ix—Fe2—O1285.13 (12)P3—O32—Fe2ii139.08 (19)
O23ix—Fe2—O1283.75 (5)P3xvi—O33—Fe3134.20 (12)
O23x—Fe2—O1283.75 (5)P3xvi—O33—Caxiii100.10 (10)
O—Fe2—O1192.67 (12)Fe3—O33—Caxiii125.55 (9)
O32ix—Fe2—O11151.41 (11)Fe2—O—Fe1xvii125.79 (7)
O23ix—Fe2—O1189.23 (6)Fe2—O—Fe1ix125.79 (7)
O23x—Fe2—O1189.23 (6)Fe1xvii—O—Fe1ix105.66 (12)
O12—Fe2—O1166.28 (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.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ER2067).

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