Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O

Lafuente, B.; Downs, R.T.; Yang, H.; Jenkins, R.A.

doi:10.1107/S1600536814004061

inorganic compounds

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Volume 70| Part 3| March 2014| Pages i16-i17

doi:10.1107/S1600536814004061

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Calcioferrite with composition (Ca_3.94Sr_0.06)Mg_1.01(Fe_2.93Al_1.07)(PO₄)₆(OH)₄·12H₂O

Barbara Lafuente,^a ^* Robert T. Downs,^a Hexiong Yang ^a and Robert A. Jenkins ^a

^aDepartment of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
^*Correspondence e-mail: barbaralafuente@email.arizona.edu

(Received 12 February 2014; accepted 21 February 2014; online 28 February 2014)

Calcioferrite, ideally Ca₄MgFe³⁺₄(PO₄)₆(OH)₄·12H₂O (tetracalcium magnesium tetrairon(III) hexakis-phosphate tetrahydroxide dodecahydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca₄AB₄(PO₄)₆(OH)₄·12H₂O, where A = Mg, Fe²⁺, Mn²⁺ and B = Al, Fe³⁺. Calcioferrite and the other three known members of the group, montgomeryite (A = Mg, B = Al), kingsmountite (A = Fe²⁺, B = Al), and zodacite (A = Mn²⁺, B = Fe³⁺), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca_3.94Sr_0.06)Mg_1.01(Fe_2.93Al_1.07)(PO₄)₆(OH)₄·12H₂O based on single-crystal X-ray diffraction data collected from a natural sample from the Moculta quarry in Angaston, Australia. Calcioferrite is isostructural with montgomeryite, the only member of the group with a reported structure. The calcioferrite structure is characterized by (Fe/Al)O₆ octahedra (site symmetries 2 and -1) sharing corners (OH) to form chains running parallel to [101]. These chains are linked together by PO₄ tetrahedra (site symmetries 2 and 1), forming [(Fe/Al)₃(PO₄)₃(OH)₂] layers stacking along [010], which are connected by (Ca/Sr)²⁺ cations (site symmetry 2) and Mg²⁺ cations (site symmetry 2; half-occupation). Hydrogen-bonding interactions involving the water molecules (one of which is equally disordered over two positions) and OH function are also present between these layers. The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010).

CCDC reference: 988095

Related literature

For background references to calcioferrite, see: Blum (1858 ); Palache et al. (1951 ); Henderson & Peisley (1985 ). For discussions on minerals isostructural with calcioferrite, see: Larsen (1940 ); Moore & Araki (1974 ); Fanfani et al. (1976 ); Dunn et al. (1979 , 1983 , 1988 ). For information on phosphate minerals, see: Mead & Mrose (1968 ); Huminicki & Hawthorne (2002 ). For details of rigid-body thermal motion of atoms in crystals, see: Downs (2000 ).

Experimental

Crystal data

(Ca_3.94Sr_0.06)Mg_1.01(Fe_2.93Al_1.07)(PO₄)₆(OH)₄·12H₂O
M_r = 1234.28
Monoclinic, C 2/c
a = 10.1936 (8) Å
b = 24.1959 (18) Å
c = 6.3218 (4) Å
β = 91.161 (4)°
V = 1558.9 (2) Å³
Z = 2
Mo Kα radiation
μ = 2.60 mm⁻¹
T = 293 K
0.09 × 0.08 × 0.05 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ) T_min = 0.800, T_max = 0.881
10490 measured reflections
2348 independent reflections
1712 reflections with I > 2σ(I)
R_int = 0.049

Refinement

R[F² > 2σ(F²)] = 0.039
wR(F²) = 0.094
S = 1.01
2348 reflections
160 parameters
4 restraints
All H-atom parameters refined
Δρ_max = 0.57 e Å⁻³
Δρ_min = −0.60 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
OW1—H11⋯O3ⁱ	0.72 (3)	2.40 (4)	2.994 (4)	142 (5)
OW1—H11⋯O6ⁱ	0.72 (3)	2.41 (3)	3.079 (4)	155 (5)
OW1—H12⋯OH	0.74 (3)	2.45 (3)	3.145 (4)	159 (4)
OW1—H12⋯O2	0.74 (3)	2.75 (4)	3.179 (4)	120 (4)
OW2—H21⋯O5	1.00 (4)	1.61 (4)	2.606 (3)	174 (4)
OW2—H22⋯OW3Bⁱ	0.86 (4)	2.02 (4)	2.841 (9)	160 (4)
OW2—H22⋯OW3Aⁱ	0.86 (4)	2.27 (4)	3.033 (10)	148 (4)
OW2—H22⋯O6ⁱⁱ	0.86 (4)	2.57 (4)	2.973 (4)	109 (3)
OH—H1⋯OW1ⁱ	0.69 (4)	2.22 (4)	2.891 (4)	165 (5)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (ii) $[x, -y, z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 988095

Crystal structure: contains datablock I. DOI: 10.1107/S1600536814004061/wm5004sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536814004061/wm5004Isup2.hkl

checkCIF report

Comment top

Calcioferrite was originally described by Blum (1858) from a sample found in Battenberg (Rhenish, Bavaria) with the chemical composition (wt.%): P₂O₅ 34.01, Fe₂O₃ 24.34, Al₂O₃ 2.90, CaO 14.81, MgO 2.65, and H₂O 20.56 (total = 99.27). Larsen (1940) reported montgomeryite with an ideal chemical formula Ca₄Al₅(PO₄)₆(OH)₅.11H₂O without recognizing its relationship to calcioferrite. Palache et al. (1951), on the basis of the chemistry given by Blum (1858), proposed the chemical formula Ca₃Fe₃(PO₄)₄(OH)₃.8H₂O for calcioferrite. By comparing chemical compositions and X-ray powder diffraction profiles between calcioferrite and montgomeryite, Mead & Mrose (1968) suggested that these two minerals are isostructural. Moore & Araki (1974) first solved the structure of montgomeryite in space group C2/c and revised its chemical formula to Ca₄MgAl₄(PO₄)₆(OH)₄.12H₂O. Nevertheless, Fanfani et al. (1976) observed the presence of some weak reflections that violate the C2/c space group symmetry for montgomeryite, leading them to propose C2 as the actual space group for this mineral. Dunn et al. (1983) studied red montgomeryite from the Tip Top Pegmatite and also concluded that calcioferrite is the Fe³⁺ analog of montgomeryite based on the similarity between their X-ray powder diffraction patterns. Consequently, they modified the ideal chemical formula of calcioferrite to its present form, Ca₄MgFe³⁺₄(PO₄)₆(OH)₄.12H₂O.

A second locality for calcioferrite was reported by Henderson & Peisley (1985) at the Moculta quarry in Angaston, South Australia, associated with apatite, jarosite, cacoxenite and altered pyrite, the latter probably being the source of Fe³⁺. The chemistry and X-ray power data of calcioferrite from this locality are consistent with the previous observations that calcioferrite is isotypic with montgomeryite. However, the structure of calcioferrite has remained undetermined because of its small crystal size and generally poor crystallinity. In the course of identifying minerals for the RRUFF Project (http://rruff.info), we were able to isolate a single crystal of calcioferrite and determine its structure by means of single-crystal X-ray diffraction, demonstrating that its space group is C2/c.

The general composition of the calcioferrite group minerals can be expressed as Ca₄AB₄(PO₄)₆(OH)₄.12H₂O with A = Mg, Fe²⁺, Mn²⁺ and B = Al, Fe³⁺. In addition to calcioferrite, there are three other known members in the group, including montgomeryite (A = Mg, B = Al) (Moore & Araki, 1974; Fanfani et al., 1976), kingsmountite (A = Fe²⁺, B = Al) (Dunn et al., 1979), and zodacite (A = Mn²⁺, B = Fe³⁺) (Dunn et al., 1988). The structure of calcioferrite contains seven non-hydrogen cation sites, two for Ca [((Cal/Sr1); site symmetry 2; occupancy ratio Ca:Sr =0.97:0.03) and Ca2 (site symmetry 2)], two for Fe [((Fe1/Al1); site symmetry 1; occupancy ratio Fe:Al = 0.651:0.349) and (Fe2/Al2; site symmetry 2; occupancy ratio Fe:Al = 0.814:0.186)], one for Mg [site symmetry 2; half-occupation], and two for P [(P1; site symmetry 2) and P2 (site symmetry 1)]. The chains of corner-sharing (Fe/Al)O₆ octahedra (parallel to [101]) are linked together by PO₄ tetrahedra to form [(Fe/Al)₃(PO₄)₃(OH)₂] layers stacking along [010] (Figs. 1, 2). The configuration of such layers has been observed in many others (Fe/Al)³⁺ phosphates (Huminicki & Hawthorne, 2002). The [(Fe/Al)₃(PO₄)₃(OH)₂] layers are connected by Ca²⁺ cations (coordination numbers of eight) and Mg²⁺ cations (coordination number of six). The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010).

The (Fe/Al)O₆ octahedral chains in calcioferrite have a repeat of ~7.1 Å, similar to those examined by Huminicki & Hawthorne (2002). Between the two distinct B sites, the B1 site is strongly preferred by Al. The average (Fe/Al)1—O distance is 1.962 Å, which is evidently shorter than the average (Fe/Al)2—O distance (1.997 Å). The analysis of the anisotropic displacement parameters of atoms indicates that PO₄ tetrahedra behave as rigid bodies, as should be expected for such strongly bonded tetrahedral groups (Downs, 2000). Both (Ca/Sr)1 and Ca2 are eight-coordinated, with the former by (4 O + 4 H₂O) and the latter by (6 O + 2 H₂O). The (Ca/Sr)1O₈ polyhedra are situated between the [(Fe/Al)₃(PO₄)₃(OH)₂] layers, whereas the Ca2O₈ polyhedra are located within the layers (Fig. 2). Hydrogen-bonding interactions involving the water molecules and OH- function are also present between these layers (Table 1).

As observed for the (Ca/Sr)1O₈ polyhedra, the MgO₆ octahedra are also located between the [(Fe/Al)₃(PO₄)₃(OH)₂] layers (Fig. 2). The Mg-site is randomly half-occupied with an average Mg—O bond length of 1.988 Å. The water O atom OW3 appears to be split between two positions (OW3A and OW3B), representing the two sets of water molecules correlated to the occupancy of the Mg-site (Fig. 3). The displacement parameters for OW3A are significantly larger and elongated than those of OW3B, suggesting that OW3A correlates with the vacancy and therefore is in a "softer" potential well. Interatomic distances between Mg—OW3B are more similar to each other (2.145 (8) Å and 2.200 (9) Å) while those between Mg—OW3A are more dissimilar to each other (2.535 (11) Å and 2.117 (10) Å). This is consistent with our suggestion, based on displacement parameters, that OW3A is not bonded to Mg.

Experimental top

The calcioferrite specimen used in this study is from Moculta quarry, Angaston, Australia, and is in the collection of the RRUFF project (deposition R120092: http://rruff.info/R120092). Its chemical composition was determined with a CAMECA SX100 electron microprobe at the conditions of 15kV, 1nA and a beam size of 5µm. These conditions were optimized to minimize sample damage by the electron beam due to the small size of the sample (Fig. 4) and its high hydration. Ten analysis points yielded an average composition (wt. %): CaO 17.40 (41), SrO 0.57 (21), MgO 3.24 (16), Fe₂O₃ 18.51(1.44), Al₂O₃ 4.29 (86) and P₂O₅ 34.97 (86), with H₂O 21.02 calculated by difference. Due to the significant dehydration of the sample during the electron microprobe analysis, this composition may not be very accurate and was used only for the estimation of cation ratios. By assuming six P cations per formula, the relative ratio of (Ca, Sr):Mg:(Fe, Al):P is 3.85:0.98:3.85:6.00. The composition of the crystal is then (Ca_3.94Sr_0.06)_Σ₌₄Mg(Fe_2.93Al_1.07)_Σ₌₄(PO₄)₆(OH)₄.12H₂O as determined by the combination of the electron microprobe and the X-ray structural data.

Refinement top

All non-hydrogen atoms were refined with anisotropic displacement parameters. Only H atoms bonded to OW1, OW2, and OH could be located from difference Fourier syntheses and their positions refined with a fixed isotropic displacement parameter (U_iso = 0.03). The H atoms bonded to the disordered OW3 atom could not be located and were excluded from refinement.

The occupancies of Al and Fe of the two B sites were refined with their ratio determined from the electron microprobe analysis. The small amount of Sr detected from the electron microprobe analysis was assigned into the Ca1 site, because this site is significantly larger than the Ca2 site. The maximum residual electron density in the difference Fourier map, 0.57 e/Å³, was located at (0, 0.0340, 0.25), 0.69 Å from Sr1 and the minimum, -0.60 e/Å³, at (0.8637, 0.3318, 0.0082), 1.31 Å from OW1.

Related literature top

For background references to calcioferrite, see: Blum (1858); Palache et al. (1951); Henderson & Peisley (1985). For discussions on minerals isostructural with calcioferrite, see: Larsen (1940); Moore & Araki (1974); Fanfani et al. (1976); Dunn et al. (1979, 1983, 1988). For information on phosphate minerals, see: Mead & Mrose (1968); Huminicki & Hawthorne (2002). For details of rigid-body thermal motion of atoms in crystals, see: Downs (2000).

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. A slice of the calcioferrite structure, showing the [(Fe/Al)₃(PO₄)₃(OH)₂] layer. Yellow octahedra, purple tetrahedra and red spheres represent (Fe/Al)O₆, PO₄ and OH groups, respectively.
	Fig. 2. The [(Fe/Al)₃(PO₄)₃(OH)₂] layers are stacked along [010]. They are connected by H₂O and cations Ca²⁺ and Mg²⁺. Yellow and green octahedra represent (Fe/Al)O₆ and MgO₆ groups, respectively. Purple tetrahedra represent PO₄ groups. Grey, aquamarine, blue and red spheres represent Ca²⁺ cations, H₂O molecules, H atoms and O atoms, respectively.
	Fig. 3. The crystal structure of calcioferrite showing atoms with anisotropic displacement ellipsoids at the 99% probability level. Yellow, purple, green and grey ellipsoids represent (Fe/Al), P, Mg and Ca sites, respectively. Red and aquamarine ellipsoids represent O atoms and H₂O groups, respectively. Small blue spheres represent H atoms.
	Fig. 4. A backscattered electron image of calcioferrite crystals.

Tetracalcium magnesium tetrairon(III) hexakis-phosphate tetrahydroxide dodecahydrate top

Crystal data top

Ca₄MgFe₄(PO₄)₆(OH)₄·12H₂O	F(000) = 1243
M_r = 1234.28	D_x = 2.629 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2019 reflections
a = 10.1936 (8) Å	θ = 2.2–29.9°
b = 24.1959 (18) Å	µ = 2.60 mm⁻¹
c = 6.3218 (4) Å	T = 293 K
β = 91.161 (4)°	Plate, pale yellow
V = 1558.9 (2) Å³	0.09 × 0.08 × 0.05 mm
Z = 2

Data collection top

Bruker APEXII CCD area-detector diffractometer	2348 independent reflections
Radiation source: fine-focus sealed tube	1712 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.049
φ and ω scan	θ_max = 30.5°, θ_min = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2004)	h = −14→14
T_min = 0.800, T_max = 0.881	k = −34→34
10490 measured reflections	l = −8→8

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.039	All H-atom parameters refined
wR(F²) = 0.094	w = 1/[σ²(F_o²) + (0.0509P)²] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max = 0.002
2348 reflections	Δρ_max = 0.57 e Å⁻³
160 parameters	Δρ_min = −0.60 e Å⁻³
4 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0012 (3)

Crystal data top

Ca₄MgFe₄(PO₄)₆(OH)₄·12H₂O	V = 1558.9 (2) Å³
M_r = 1234.28	Z = 2
Monoclinic, C2/c	Mo Kα radiation
a = 10.1936 (8) Å	µ = 2.60 mm⁻¹
b = 24.1959 (18) Å	T = 293 K
c = 6.3218 (4) Å	0.09 × 0.08 × 0.05 mm
β = 91.161 (4)°

Data collection top

Bruker APEXII CCD area-detector diffractometer	2348 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2004)	1712 reflections with I > 2σ(I)
T_min = 0.800, T_max = 0.881	R_int = 0.049
10490 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.039	4 restraints
wR(F²) = 0.094	All H-atom parameters refined
S = 1.01	Δρ_max = 0.57 e Å⁻³
2348 reflections	Δρ_min = −0.60 e Å⁻³
160 parameters

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	Occ. (<1)
Ca1	0.0000	0.06262 (3)	0.2500	0.0138 (2)	0.9700 (1)
Sr1	0.0000	0.06262 (3)	0.2500	0.0138 (2)	0.0300 (1)
Ca2	0.0000	0.33191 (4)	0.2500	0.0155 (2)
Mg	0.0000	0.47193 (12)	0.2500	0.0130 (6)	0.5050 (1)
Fe1	0.2500	0.2500	0.0000	0.0076 (2)	0.651 (3)
Al1	0.2500	0.2500	0.0000	0.0076 (2)	0.349 (3)
Fe2	0.0000	0.16865 (3)	−0.2500	0.00762 (17)	0.814 (3)
Al2	0.0000	0.16865 (3)	−0.2500	0.00762 (17)	0.186 (3)
P1	0.5000	0.30208 (5)	−0.2500	0.0115 (2)
P2	0.26354 (8)	0.11351 (3)	0.96145 (13)	0.01383 (19)
O1	0.6135 (2)	0.26286 (10)	0.7074 (4)	0.0198 (5)
O2	0.4700 (2)	0.34019 (9)	0.5625 (3)	0.0164 (5)
O3	0.3130 (2)	0.17285 (9)	0.0051 (4)	0.0189 (5)
O4	0.3782 (2)	0.08573 (9)	0.8546 (4)	0.0201 (5)
O5	0.1438 (2)	0.11435 (9)	0.8055 (4)	0.0192 (5)
O6	0.2234 (3)	0.08585 (10)	0.1650 (4)	0.0284 (6)
OH	0.3675 (2)	0.27149 (10)	0.2343 (4)	0.0173 (5)
OW1	0.1598 (3)	0.32890 (13)	0.5225 (4)	0.0314 (7)
OW2	0.1120 (2)	0.02555 (10)	0.5770 (4)	0.0229 (5)
OW3A	0.1164 (9)	0.4665 (4)	0.6075 (13)	0.0281 (17)	0.50
OW3B	0.1193 (8)	0.4792 (3)	0.5320 (12)	0.0199 (15)	0.50
H11	0.178 (4)	0.3424 (18)	0.620 (6)	0.030*
H12	0.213 (4)	0.3114 (17)	0.483 (7)	0.030*
H21	0.123 (4)	0.0581 (17)	0.673 (6)	0.030*
H22	0.191 (4)	0.0156 (17)	0.553 (6)	0.030*
H1	0.372 (4)	0.2496 (18)	0.303 (7)	0.030*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ca1	0.0177 (4)	0.0103 (4)	0.0132 (4)	0.000	−0.0008 (3)	0.000
Sr1	0.0177 (4)	0.0103 (4)	0.0132 (4)	0.000	−0.0008 (3)	0.000
Ca2	0.0149 (4)	0.0155 (5)	0.0160 (5)	0.000	0.0010 (3)	0.000
Mg	0.0115 (14)	0.0084 (14)	0.0192 (16)	0.000	0.0000 (11)	0.000
Fe1	0.0081 (4)	0.0043 (3)	0.0104 (4)	−0.0008 (3)	0.0006 (2)	−0.0003 (3)
Al1	0.0081 (4)	0.0043 (3)	0.0104 (4)	−0.0008 (3)	0.0006 (2)	−0.0003 (3)
Fe2	0.0088 (3)	0.0055 (3)	0.0087 (3)	0.000	0.0011 (2)	0.000
Al2	0.0088 (3)	0.0055 (3)	0.0087 (3)	0.000	0.0011 (2)	0.000
P1	0.0129 (5)	0.0102 (5)	0.0113 (5)	0.000	0.0019 (4)	0.000
P2	0.0160 (4)	0.0093 (4)	0.0164 (4)	0.0018 (3)	0.0049 (3)	0.0028 (3)
O1	0.0223 (12)	0.0176 (12)	0.0198 (12)	0.0062 (9)	0.0083 (9)	0.0031 (9)
O2	0.0220 (12)	0.0147 (11)	0.0127 (11)	0.0020 (9)	0.0022 (8)	0.0001 (8)
O3	0.0204 (12)	0.0129 (11)	0.0233 (13)	0.0027 (9)	−0.0031 (9)	−0.0033 (9)
O4	0.0196 (12)	0.0152 (12)	0.0258 (13)	0.0056 (9)	0.0068 (9)	0.0019 (9)
O5	0.0160 (12)	0.0132 (12)	0.0282 (13)	0.0031 (9)	−0.0034 (9)	−0.0036 (10)
O6	0.0324 (14)	0.0273 (15)	0.0261 (14)	0.0048 (11)	0.0138 (11)	0.0118 (11)
OH	0.0197 (12)	0.0115 (12)	0.0206 (13)	−0.0040 (9)	−0.0034 (9)	0.0048 (9)
OW1	0.0299 (16)	0.0415 (19)	0.0226 (15)	−0.0034 (13)	−0.0055 (11)	0.0040 (13)
OW2	0.0221 (13)	0.0194 (13)	0.0271 (14)	−0.0027 (11)	−0.0022 (10)	−0.0048 (10)
OW3A	0.040 (4)	0.018 (4)	0.026 (5)	0.009 (3)	−0.006 (4)	−0.005 (3)
OW3B	0.018 (3)	0.015 (4)	0.026 (5)	0.005 (2)	−0.008 (3)	0.000 (3)

Geometric parameters (Å, º) top

Ca1—O6ⁱ	2.417 (2)	Mg—OW3B^viii	2.200 (9)
Ca1—O6	2.417 (2)	Mg—OW3Aⁱ	2.535 (8)
Ca1—OW2ⁱ	2.507 (3)	Mg—OW3A	2.535 (8)
Ca1—OW2	2.507 (3)	Fe1—O1ⁱⁱⁱ	1.956 (2)
Ca1—O2ⁱⁱ	2.648 (2)	Fe1—O1^x	1.956 (2)
Ca1—O2ⁱⁱⁱ	2.648 (2)	Fe1—OH^vii	1.956 (2)
Ca1—OW2^iv	2.665 (3)	Fe1—OH	1.956 (2)
Ca1—OW2^v	2.665 (3)	Fe1—O3	1.974 (2)
Ca2—OW1ⁱ	2.348 (3)	Fe1—O3^vii	1.974 (2)
Ca2—OW1	2.348 (3)	Fe2—OH^vii	1.981 (2)
Ca2—O4ⁱⁱ	2.446 (2)	Fe2—OHⁱⁱⁱ	1.981 (2)
Ca2—O4ⁱⁱⁱ	2.446 (2)	Fe2—O5ⁱ	1.995 (2)
Ca2—O3^vi	2.524 (2)	Fe2—O5^xi	1.995 (2)
Ca2—O3^vii	2.524 (2)	Fe2—O2^vii	2.016 (2)
Ca2—O1ⁱⁱ	2.585 (3)	Fe2—O2ⁱⁱⁱ	2.016 (2)
Ca2—O1ⁱⁱⁱ	2.585 (3)	P1—O1^x	1.525 (2)
Mg—O4ⁱⁱⁱ	1.990 (3)	P1—O1^xi	1.525 (2)
Mg—O4ⁱⁱ	1.990 (3)	P1—O2^x	1.528 (2)
Mg—OW3A^viii	2.117 (10)	P1—O2^xi	1.528 (2)
Mg—OW3A^ix	2.117 (10)	P2—O6^xii	1.514 (2)
Mg—OW3Bⁱ	2.145 (8)	P2—O4	1.519 (2)
Mg—OW3B	2.145 (8)	P2—O3^xii	1.545 (2)
Mg—OW3B^ix	2.200 (9)	P2—O5	1.553 (2)

O4ⁱⁱⁱ—Mg—O4ⁱⁱ	90.93 (18)	O1ⁱⁱⁱ—Fe1—OH^vii	91.85 (10)
O4ⁱⁱⁱ—Mg—OW3A^viii	173.6 (2)	O1^x—Fe1—OH^vii	88.15 (10)
O4ⁱⁱ—Mg—OW3A^viii	89.6 (2)	OH^vii—Fe1—OH	180.00 (13)
OW3A^viii—Mg—OW3A^ix	90.5 (5)	O1ⁱⁱⁱ—Fe1—O3	94.26 (10)
O4ⁱⁱⁱ—Mg—OW3Bⁱ	89.3 (3)	O1^x—Fe1—O3	85.74 (10)
O4ⁱⁱ—Mg—OW3Bⁱ	97.4 (2)	OH^vii—Fe1—O3	87.43 (10)
OW3A^viii—Mg—OW3Bⁱ	84.3 (4)	OH—Fe1—O3	92.57 (10)
OW3A^ix—Mg—OW3Bⁱ	89.0 (2)	O3—Fe1—O3^vii	180.0
OW3Bⁱ—Mg—OW3B	170.5 (5)	OH^vii—Fe2—OHⁱⁱⁱ	86.06 (14)
O4ⁱⁱⁱ—Mg—OW3B^ix	79.2 (2)	OH^vii—Fe2—O5ⁱ	171.18 (9)
O4ⁱⁱ—Mg—OW3B^ix	160.24 (19)	OHⁱⁱⁱ—Fe2—O5ⁱ	88.56 (10)
OW3A^viii—Mg—OW3B^ix	102.1 (3)	O5ⁱ—Fe2—O5^xi	97.60 (13)
OW3A^ix—Mg—OW3B^ix	15.01 (19)	OH^vii—Fe2—O2^vii	90.57 (9)
OW3Bⁱ—Mg—OW3B^ix	99.5 (3)	OHⁱⁱⁱ—Fe2—O2^vii	98.35 (9)
OW3B—Mg—OW3B^ix	75.3 (3)	O5^xi—Fe2—O2^vii	88.68 (9)
OW3B^ix—Mg—OW3B^viii	115.1 (4)	O2^vii—Fe2—O2ⁱⁱⁱ	167.81 (13)
O4ⁱⁱⁱ—Mg—OW3Aⁱ	88.6 (2)	O1^x—P1—O1^xi	103.03 (19)
O4ⁱⁱ—Mg—OW3Aⁱ	87.2 (2)	O1^x—P1—O2^x	112.29 (12)
OW3A^viii—Mg—OW3Aⁱ	85.0 (3)	O1^xi—P1—O2^x	111.83 (13)
OW3A^ix—Mg—OW3Aⁱ	99.2 (4)	O2^x—P1—O2^xi	105.75 (18)
OW3Bⁱ—Mg—OW3Aⁱ	10.2 (3)	O6^xii—P2—O4	113.94 (14)
OW3B—Mg—OW3Aⁱ	173.1 (4)	O6^xii—P2—O3^xii	110.61 (14)
OW3B^ix—Mg—OW3Aⁱ	109.38 (17)	O4—P2—O3^xii	103.84 (13)
OW3B^viii—Mg—OW3Aⁱ	74.0 (3)	O6^xii—P2—O5	108.83 (14)
OW3Aⁱ—Mg—OW3A	174.1 (4)	O4—P2—O5	109.00 (13)
O1ⁱⁱⁱ—Fe1—O1^x	180.0	O3^xii—P2—O5	110.54 (13)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
OW1—H11···O3ⁱⁱ	0.72 (3)	2.40 (4)	2.994 (4)	142 (5)
OW1—H11···O6ⁱⁱ	0.72 (3)	2.41 (3)	3.079 (4)	155 (5)
OW1—H12···OH	0.74 (3)	2.45 (3)	3.145 (4)	159 (4)
OW1—H12···O2	0.74 (3)	2.75 (4)	3.179 (4)	120 (4)
OW2—H21···O5	1.00 (4)	1.61 (4)	2.606 (3)	174 (4)
OW2—H22···OW3Bⁱⁱ	0.86 (4)	2.02 (4)	2.841 (9)	160 (4)
OW2—H22···OW3Aⁱⁱ	0.86 (4)	2.27 (4)	3.033 (10)	148 (4)
OW2—H22···O6^xiii	0.86 (4)	2.57 (4)	2.973 (4)	109 (3)
OH—H1···OW1ⁱⁱ	0.69 (4)	2.22 (4)	2.891 (4)	165 (5)

Symmetry codes: (ii) −x+1/2, −y+1/2, −z+1; (xiii) x, −y, z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
OW1—H11···O3ⁱ	0.72 (3)	2.40 (4)	2.994 (4)	142 (5)
OW1—H11···O6ⁱ	0.72 (3)	2.41 (3)	3.079 (4)	155 (5)
OW1—H12···OH	0.74 (3)	2.45 (3)	3.145 (4)	159 (4)
OW1—H12···O2	0.74 (3)	2.75 (4)	3.179 (4)	120 (4)
OW2—H21···O5	1.00 (4)	1.61 (4)	2.606 (3)	174 (4)
OW2—H22···OW3Bⁱ	0.86 (4)	2.02 (4)	2.841 (9)	160 (4)
OW2—H22···OW3Aⁱ	0.86 (4)	2.27 (4)	3.033 (10)	148 (4)
OW2—H22···O6ⁱⁱ	0.86 (4)	2.57 (4)	2.973 (4)	109 (3)
OH—H1···OW1ⁱ	0.69 (4)	2.22 (4)	2.891 (4)	165 (5)

Symmetry codes: (i) −x+1/2, −y+1/2, −z+1; (ii) x, −y, z+1/2.

Acknowledgements

We gratefully acknowledge support for this study by the Arizona Science Foundation and NASA NNX11AP82A, Mars Science Laboratory Investigations. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the National Aeronautics and Space Administration.

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Volume 70| Part 3| March 2014| Pages i16-i17

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