Mg6.75(OH)3(H0.166AsO4)3(HAsO4), a member of the M1-xM′6(OH)3(H2x/3AsO4)3(HAsO4) family (M,M′ = Co; Ni)

Weil, M.

doi:10.1107/S1600536813010714

inorganic compounds

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Volume 69| Part 5| May 2013| Page i29

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Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄), a member of the M_1-_xM′₆(OH)₃(H_2x/3AsO₄)₃(HAsO₄) family (M,M′ = Co; Ni)

Matthias Weil ^a ^*

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at

(Received 18 April 2013; accepted 19 April 2013; online 24 April 2013)

In the structure of the title compound, magnesium hydroxide hydrogenarsenate (6.75/3/4), two different Mg²⁺ ions, one located on a site with symmetry 3m. (occupancy 3/4) and one on a general position, as well as two different AsO₃(OH) tetrahedra (symmetry .m. with partial occupancy for the H atom for one, and symmetry 3m. with full occupancy for the H atom for the other) and one OH⁻ ion (site symmetry .m.) are present. Both Mg²⁺ ions are octahedrally surrounded by O atoms. The MgO₆ octahedra belonging to the partially occupied Mg²⁺ sites share faces, forming chains along [001]. The other type of MgO₆ octahedra share corners and faces under formation of strands parallel to [001] whereby individual strands are linked through common corner atoms. The two types of AsO₃(OH) tetrahedra interlink the strands and the chains, building up a three-dimensional framework resembling that of the mineral dumortierite. The OH groups were assigned on basis of bond-valence calculations and crystal chemical considerations.

Related literature

For the isotypic Co and Ni members of the M_1-_xM′₆(OH)₃(H_2x/3AsO₄)₃(HAsO₄) series, see: Hughes et al. (2003 ). For other reaction products obtained under the given or similar hydrothermal conditions, see: Weil (2004a ,b ). For the crystal structure of dumortierite, see: Alexander et al. (1986 ). The bond-valence method has been described by Brown (2002 ).

Experimental

Crystal data

Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄)
M_r = 772.31
Hexagonal, P 6₃ m c
a = 12.7651 (3) Å
c = 5.0844 (1) Å
V = 717.49 (3) Å³
Z = 2
Mo Kα radiation
μ = 9.65 mm⁻¹
T = 296 K
0.30 × 0.02 × 0.02 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ) T_min = 0.160, T_max = 0.830
21473 measured reflections
1144 independent reflections
1066 reflections with I > 2σ(I)
R_int = 0.051

Refinement

R[F² > 2σ(F²)] = 0.029
wR(F²) = 0.058
S = 1.21
1144 reflections
60 parameters
1 restraint
H-atom parameters not refined
Δρ_max = 1.31 e Å⁻³
Δρ_min = −2.16 e Å⁻³
Absolute structure: Flack (1983 ), 446 Friedel pairs
Flack parameter: 0.022 (16)

Table 1
Selected bond lengths (Å)

Mg1—O1ⁱ	2.100 (5)
Mg1—O1ⁱⁱ	2.102 (5)
Mg1—Mg1ⁱⁱⁱ	2.5422 (1)
Mg2—O2	2.018 (3)
Mg2—O2^iv	2.029 (3)
Mg2—O5	2.036 (3)
Mg2—O3^v	2.053 (2)
Mg2—O4	2.139 (3)
Mg2—O4ⁱⁱ	2.225 (3)
As1—O2	1.678 (2)
As1—O1	1.687 (4)
As1—O3	1.696 (3)
As2—O5	1.644 (3)
As2—O6ⁱⁱ	1.710 (8)
Symmetry codes: (i) x-1, y-1, z; (ii) $[-x+1, -y+1, z+{\script{1\over 2}}]$ ; (iii) $[-x, -y, z+{\script{1\over 2}}]$ ; (iv) $[y, x, z+{\script{1\over 2}}]$ ; (v) $[x-y+1, x, z-{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS for Windows (Dowty, 2006 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536813010714/vn2069sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536813010714/vn2069Isup2.hkl

checkCIF report

Comment top

Crystals of the title compound, Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄), were obtained serendipitously during crystal growth experiments intended to grow a possible descloizite-type phase 'MgHg(AsO₄)(OH)' under hydrothermal formation conditions, similar to the formation of ZnHg(AsO₄)(OH) (Weil, 2004a).

Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄) belongs to the isotypic series M_{1 -} _xM'₆(OH)₃(H₂_x_/3AsO₄)₃(HAsO₄) for which the Co and Ni members have been structurally determined by Hughes et al. (2003). The crystal structures contain two M²⁺ ions, one (M1) located on a site with symmetry 3m. and with varying partial occupancy, and the other (M2) located on a general position with full occupancy. Two different AsO₃(OH) tetrahedra, one (As1) with symmetry .m. and partial occupancy for its H atom, and the other (As2) with symmetry 3m. and full occupancy for the H atom, as well as one OH^- ion (site symmetry .m.; full occupancy for the H atom) are also present.

The two metal ions are octahedrally surrounded by O atoms, with Mg—O distances in the range 2.018 (3) to 2.225 (3) Å. The Mg1O₆ octahedra share faces forming chains parallel to [001]. Mg2O₆ octahedra share faces and edges forming strands parallel to [001] (Fig. 1). Individual strands are linked with neighbouring strands through common corner atoms. The AsO₃(OH) tetrahedra flank the chains and strands and link both motifs into a three-dimensional framework (Fig. 2).

Since the protons required for charge balance could not be located from difference maps, the assignment of OH groups was made both from crystal chemical considerations and calculation of bond valence sums (Brown, 2002). The valence sums for Mg1 (1.99 v.u.), Mg2 (2.13), As1 (5.00) and As2 (5.34) are near the expected values of 2 and 5, respectively. The values of 1.90 for O1, 2.09 for O2, 2.00 for O3, 1.07 for O4, 2.19 for O5 and 1.17 for O6 suggest that O1, O4 and O6 belong to hydroxide groups; the occupancy of the attached H atom sites of O1 is 0.166 and is dependent on the occupancy of the Mg1 site to which the As1O₃(OH) group is attached. H atoms attached to O4 and O6 are fully occupied. O4 is the OH group bonded to four Mg2²⁺ cations. For this bridging µ₄ group the longest Mg—O distances of 2.139 (3) and 2.225 (3) Å are observed. O6 is the OH group of an As2O₃(OH) tetrahedron; it is solely bonded to As2 and is a much longer (As2—O6(H) = 1.710 (8) Å) than the As2—O5 bonds (1.644 (3) Å) which is typical for AsO₃(OH) units.

An interesting feature of this structure type is the short M···M contact within the chains of face-sharing M1O₆ octahedra running along [001]. The observed Mg···Mg distance of 2.5422 (1) Å corresponds to c/2 and lies between the respective distances of 2.5460 (1) Å for the Co and of 2.4843 (5) Å for the Ni member (Hughes et al., 2003).

The topological similarities between the framework structure of the title compound and that of the minerals dumortierite (Alexander et al., 1986) and cancrinite has been discussed in detail by Hughes et al. (2003).

Related literature top

For the isotypic Co and Ni members of the M_1-_xM'₆(OH)₃(H₂_x_/3AsO₄)₃(HAsO₄) series, see: Hughes et al. (2003). For other reaction products obtained under the given or similar hydrothermal conditions, see: Weil (2004a,b). For the crystal structure of dumortierite, see: Alexander et al. (1986). The bond-valence method has been described by Brown (2002).

Experimental top

200 mg of an amorphous precipitation product obtained by reacting MgCO₃ and arsenic acid (ca 20%_wt) was mixed with 300 mg HgO and placed in a Teflon container (volume 10 ml) that was filled up with two-thirds of its volume with water. The inlay was placed in a steel autoclave and heated at 493 K for two weeks. Besides colourless needle-shaped crystals of the title compound, recrystallized HgO and α-(Hg₂)₃(AsO₄)₂ (Weil, 2004b) were also present, as determined by single-crystal X-ray diffraction of selected crystals.

Structure description top

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS for Windows (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

	Fig. 1. Strands of face- and edge-sharing Mg2O₆ octahedra extending parallel to [001]. Atoms are displayed with anisotropic displacement parameters at the 74% level. The O atom (O4) of the OH group is given in green.
	Fig. 2. The crystal structure of the title compound in a projection along [001]. MgO₆ octahedra are blue, AsO₄ tetrahedra red. O atoms are displayed with anisotropic displacement parameters at the 74% level. O atoms belongig to OH groups (with fully or partly occupied H atoms) are given in green.

Magnesium hydroxide hydrogenarsenate (6.75/3/4) top

Crystal data top

Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄)	D_x = 3.575 Mg m⁻³
M_r = 772.31	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P6₃mc	Cell parameters from 5443 reflections
Hall symbol: P 6c -2c	θ = 6.2–34.4°
a = 12.7651 (3) Å	µ = 9.65 mm⁻¹
c = 5.0844 (1) Å	T = 296 K
V = 717.49 (3) Å³	Needle, colourless
Z = 2	0.30 × 0.02 × 0.02 mm
F(000) = 739

Data collection top

Bruker APEXII CCD diffractometer	1144 independent reflections
Radiation source: fine-focus sealed tube	1066 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.051
ω and φ scans	θ_max = 36.2°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −21→21
T_min = 0.160, T_max = 0.830	k = −21→21
21473 measured reflections	l = −5→8

Refinement top

Refinement on F²	H-atom parameters not refined
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0061P)² + 2.8884P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.029	(Δ/σ)_max < 0.001
wR(F²) = 0.058	Δρ_max = 1.31 e Å⁻³
S = 1.21	Δρ_min = −2.16 e Å⁻³
1144 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
60 parameters	Extinction coefficient: 0.0015 (4)
1 restraint	Absolute structure: Flack (1983), 446 Friedel pairs
Primary atom site location: isomorphous structure methods	Absolute structure parameter: 0.022 (16)

Crystal data top

Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄)	Z = 2
M_r = 772.31	Mo Kα radiation
Hexagonal, P6₃mc	µ = 9.65 mm⁻¹
a = 12.7651 (3) Å	T = 296 K
c = 5.0844 (1) Å	0.30 × 0.02 × 0.02 mm
V = 717.49 (3) Å³

Data collection top

Bruker APEXII CCD diffractometer	1144 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2008)	1066 reflections with I > 2σ(I)
T_min = 0.160, T_max = 0.830	R_int = 0.051
21473 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.029	H-atom parameters not refined
wR(F²) = 0.058	Δρ_max = 1.31 e Å⁻³
S = 1.21	Δρ_min = −2.16 e Å⁻³
1144 reflections	Absolute structure: Flack (1983), 446 Friedel pairs
60 parameters	Absolute structure parameter: 0.022 (16)
1 restraint

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)
Mg1	0.0000	0.0000	0.8698 (12)	0.0227 (15)	0.750 (14)
Mg2	0.65062 (9)	0.57400 (10)	0.5491 (3)	0.0085 (2)
As1	0.69764 (4)	0.848821 (19)	0.57265 (9)	0.00778 (9)
As2	0.6667	0.3333	0.78398 (17)	0.00550 (14)
O1	0.8487 (3)	0.92434 (17)	0.6201 (9)	0.0257 (10)
O2	0.6564 (2)	0.7229 (2)	0.3969 (5)	0.0100 (4)
O3	0.6168 (3)	0.80839 (17)	0.8561 (7)	0.0115 (6)
O4	0.52447 (15)	0.47553 (15)	0.2427 (7)	0.0091 (6)
O5	0.59609 (16)	0.40391 (16)	0.6823 (8)	0.0173 (8)
O6	0.3333	0.6667	0.6202 (15)	0.0319 (19)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Mg1	0.0120 (13)	0.0120 (13)	0.044 (4)	0.0060 (6)	0.000	0.000
Mg2	0.0103 (4)	0.0092 (4)	0.0073 (5)	0.0059 (3)	−0.0005 (4)	0.0001 (4)
As1	0.01061 (18)	0.00811 (12)	0.00544 (16)	0.00530 (9)	−0.0004 (2)	−0.00021 (10)
As2	0.00468 (17)	0.00468 (17)	0.0071 (3)	0.00234 (9)	0.000	0.000
O1	0.0089 (14)	0.0320 (17)	0.029 (3)	0.0044 (7)	−0.0038 (16)	−0.0019 (8)
O2	0.0141 (10)	0.0099 (9)	0.0072 (10)	0.0070 (8)	−0.0016 (8)	−0.0015 (8)
O3	0.0188 (16)	0.0110 (10)	0.0074 (14)	0.0094 (8)	0.0073 (12)	0.0036 (6)
O4	0.0099 (10)	0.0099 (10)	0.0082 (14)	0.0053 (11)	0.0009 (5)	−0.0009 (5)
O5	0.0099 (10)	0.0099 (10)	0.034 (2)	0.0065 (12)	−0.0037 (7)	0.0037 (7)
O6	0.042 (3)	0.042 (3)	0.011 (4)	0.0212 (15)	0.000	0.000

Geometric parameters (Å, º) top

Mg1—O1ⁱ	2.100 (5)	Mg2—O3^x	2.053 (2)
Mg1—O1ⁱⁱ	2.100 (5)	Mg2—O4	2.139 (3)
Mg1—O1ⁱⁱⁱ	2.100 (5)	Mg2—O4^iv	2.225 (3)
Mg1—O1^iv	2.102 (5)	As1—O2	1.678 (2)
Mg1—O1^v	2.102 (5)	As1—O2^xi	1.678 (2)
Mg1—O1^vi	2.102 (5)	As1—O1	1.687 (4)
Mg1—Mg1^vii	2.5422 (1)	As1—O3	1.696 (3)
Mg1—Mg1^viii	2.5422 (1)	As2—O5ⁱⁱ	1.644 (3)
Mg2—O2	2.018 (3)	As2—O5^xii	1.644 (3)
Mg2—O2^ix	2.029 (3)	As2—O5	1.644 (3)
Mg2—O5	2.036 (3)	As2—O6^iv	1.710 (8)

O1ⁱ—Mg1—O1ⁱⁱ	87.2 (2)	O2—As1—O2^xi	106.56 (16)
O1ⁱ—Mg1—O1ⁱⁱⁱ	87.2 (2)	O2—As1—O1	110.19 (12)
O1ⁱⁱ—Mg1—O1ⁱⁱⁱ	87.2 (2)	O2^xi—As1—O1	110.19 (12)
O1ⁱ—Mg1—O1^iv	179.9 (3)	O2—As1—O3	108.02 (11)
O1ⁱⁱ—Mg1—O1^iv	92.81 (9)	O2^xi—As1—O3	108.02 (11)
O1ⁱⁱⁱ—Mg1—O1^iv	92.81 (9)	O1—As1—O3	113.6 (2)
O1ⁱ—Mg1—O1^v	92.81 (9)	O5ⁱⁱ—As2—O5^xii	110.58 (15)
O1ⁱⁱ—Mg1—O1^v	179.9 (3)	O5ⁱⁱ—As2—O5	110.58 (15)
O1ⁱⁱⁱ—Mg1—O1^v	92.81 (9)	O5^xii—As2—O5	110.58 (15)
O1^iv—Mg1—O1^v	87.1 (2)	O5ⁱⁱ—As2—O6^iv	108.33 (15)
O1ⁱ—Mg1—O1^vi	92.81 (9)	O5^xii—As2—O6^iv	108.33 (15)
O1ⁱⁱ—Mg1—O1^vi	92.81 (9)	O5—As2—O6^iv	108.33 (15)
O1ⁱⁱⁱ—Mg1—O1^vi	179.9 (3)	As1—O1—Mg1^xiii	151.0 (3)
O1^iv—Mg1—O1^vi	87.1 (2)	As1—O1—Mg1^xiv	134.5 (3)
O1^v—Mg1—O1^vi	87.1 (2)	Mg1^xiii—O1—Mg1^xiv	74.46 (12)
O2—Mg2—O2^ix	93.03 (10)	As1—O2—Mg2	122.99 (14)
O2—Mg2—O5	164.45 (12)	As1—O2—Mg2^xv	137.98 (14)
O2^ix—Mg2—O5	95.00 (14)	Mg2—O2—Mg2^xv	98.03 (11)
O2—Mg2—O3^x	89.84 (12)	As1—O3—Mg2^ix	121.83 (9)
O2^ix—Mg2—O3^x	98.49 (13)	As1—O3—Mg2^xvi	121.83 (9)
O5—Mg2—O3^x	102.09 (14)	Mg2^ix—O3—Mg2^xvi	115.94 (18)
O2—Mg2—O4	86.36 (11)	Mg2—O4—Mg2^xvii	84.17 (14)
O2^ix—Mg2—O4	162.38 (12)	Mg2—O4—Mg2^xiv	147.49 (17)
O5—Mg2—O4	81.96 (12)	Mg2^xvii—O4—Mg2^xiv	88.83 (7)
O3^x—Mg2—O4	99.12 (14)	Mg2—O4—Mg2^xv	88.83 (7)
O2—Mg2—O4^iv	89.76 (11)	Mg2^xvii—O4—Mg2^xv	147.49 (17)
O2^ix—Mg2—O4^iv	83.86 (11)	Mg2^xiv—O4—Mg2^xv	80.23 (13)
O5—Mg2—O4^iv	77.91 (13)	As2—O5—Mg2^xvii	134.44 (9)
O3^x—Mg2—O4^iv	177.63 (15)	As2—O5—Mg2	134.44 (9)
O4—Mg2—O4^iv	78.53 (7)	Mg2^xvii—O5—Mg2	89.51 (15)

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

Experimental details

Crystal data
Chemical formula	Mg_6.75(OH)₃(H_0.166AsO₄)₃(HAsO₄)
M_r	772.31
Crystal system, space group	Hexagonal, P6₃mc
Temperature (K)	296
a, c (Å)	12.7651 (3), 5.0844 (1)
V (Å³)	717.49 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	9.65
Crystal size (mm)	0.30 × 0.02 × 0.02

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2008)
T_min, T_max	0.160, 0.830
No. of measured, independent and observed [I > 2σ(I)] reflections	21473, 1144, 1066
R_int	0.051
(sin θ/λ)_max (Å⁻¹)	0.831

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.058, 1.21
No. of reflections	1144
No. of parameters	60
No. of restraints	1
H-atom treatment	H-atom parameters not refined
Δρ_max, Δρ_min (e Å⁻³)	1.31, −2.16
Absolute structure	Flack (1983), 446 Friedel pairs
Absolute structure parameter	0.022 (16)

Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS for Windows (Dowty, 2006), publCIF (Westrip, 2010).

Selected bond lengths (Å) top

Mg1—O1ⁱ	2.100 (5)	Mg2—O4	2.139 (3)
Mg1—O1ⁱⁱ	2.102 (5)	Mg2—O4ⁱⁱ	2.225 (3)
Mg1—Mg1ⁱⁱⁱ	2.5422 (1)	As1—O2	1.678 (2)
Mg2—O2	2.018 (3)	As1—O1	1.687 (4)
Mg2—O2^iv	2.029 (3)	As1—O3	1.696 (3)
Mg2—O5	2.036 (3)	As2—O5	1.644 (3)
Mg2—O3^v	2.053 (2)	As2—O6ⁱⁱ	1.710 (8)

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

Acknowledgements

The X-ray centre of the Vienna University of Technology is acknowledged for financial support and for providing access to the single-crystal diffractometer.

References

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