A new hydrate of magnesium carbonate, MgCO3·6H2O

Rincke, C.; Schmidt, H.; Voigt, W.

doi:10.1107/S2053229620001540

research papers

STRUCTURAL
CHEMISTRY

ISSN: 2053-2296

Volume 76| Part 3| March 2020| Pages 244-249

https://doi.org/10.1107/S2053229620001540

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A new hydrate of magnesium carbonate, MgCO₃·6H₂O

Christine Rincke,^a ^* Horst Schmidt ^a and Wolfgang Voigt ^a

^aInstitute of Inorganic Chemistry, TU Bergakademie Freiberg, Leipziger Strasse 29, D-09599 Freiberg, Germany
^*Correspondence e-mail: christine.rincke@chemie.tu-freiberg.de

Edited by V. Langer, Chalmers University of Technology, Sweden (Received 30 October 2019; accepted 4 February 2020; online 13 February 2020)

During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexahydrate (MgCO₃·6H₂O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge-linked isolated pairs of Mg(CO₃)(H₂O)₄ octahedra and noncoordinating water molecules, and exhibits similarities to NiCO₃·5.5H₂O (hellyerite). The recorded X-ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO₃·3H₂O) at room temperature.

Keywords: magnesium; carbonate; low-temperature hydrate; Raman spectroscopy; crystal structure.

CCDC reference: 1981730

1. Introduction

In the MgO–H₂O–CO₂ system, besides the thermodynamically stable MgCO₃ (magnesite), a variety of hydrated magnesium carbonates are known, which can be divided in basic magnesium carbonates, containing OH⁻ ions [Mg₅(CO₃)₄(OH)₂·nH₂O and Mg(CO₃)(OH)₂·nH₂O], and neutral magnesium carbonates with the composition MgCO₃·nH₂O (Hopkinson et al., 2012 ; Jauffret et al., 2015 ). All these phases are of significant relevance in various technological processes, in geological explorations, mineral conversion in the sequestration of CO₂ and in biomineralization (Chaka & Felmy, 2014 ). Nevertheless, there are many open questions with respect to the conditions of formation, the characterization, the crystal structure and the stability of higher hydrated neutral magnesium carbonates (Hänchen et al., 2008 ; Hopkinson et al., 2012; Rincke, 2018 ).

The most frequently investigated neutral magnesium carbonate hydrate, MgCO₃·3H₂O (mineral name: nesquehonite), can be synthesized in the temperature range between 283.15 and 325.15 K (Giester et al., 2000 ; Frost & Palmer, 2011 ; Jauffret et al., 2015; Hänchen et al., 2008; Gloss, 1937 ; Takahashi & Hokoku, 1927 ; Hopkinson et al., 2012).

At lower temperatures, the pentahydrate, i.e. MgCO₃·5H₂O (mineral name: lansfordite), is known. Its crystal structure (monoclinic space group P2₁/m) was determined by Liu et al. (1990 ) from a synthetic sample and by Nestola et al. (2017 ) from a mineral. Several possibilities are described to synthesize lansfordite (Ming & Franklin, 1985 ; Liu et al., 1990). In order to obtain large prismatic crystals, CO₂ can be bubbled through an aqueous suspension of MgO and, subsequently, the crystallization can be carried out in the filtered solution at low temperature (Liu et al., 1990). However, the authors (Liu et al., 1990) did not provide information about the exact CO₂ pressure, the regime of temperature, the concentration of magnesium ions in the solution and the time needed for crystallization. According to Ming & Franklin (1985), these factors are important to avoid the formation of nesquehonite. Furthermore, the solubility of lansfordite is highly dependent on temperature and on CO₂ pressure (Königsberger et al., 1999 ; Takahashi & Hokoku, 1927; Rincke, 2018). Besides that, there are contradictory statements about the temperature and the rate of conversion of the pentahydrate to the trihydrate. Some research groups have recorded a transition temperature between 283.15 and 288.15 K (Takahashi & Hokoku, 1927; Gloss, 1937; Yanaťeva & Rassonskaya, 1961 ; Hill et al., 1982 ; Langmuir, 1965 ; Ming & Franklin, 1985), while others observed the stability of synthesized and natural samples of lansfordite at room temperature over a period of a few months (Liu et al., 1990; Nestola et al., 2017). Neutral magnesium carbonates with a water content greater than five units per formula are not known up to now. Such highly hydrated neutral carbonates of other bivalent metal ions have been found only for calcium, i.e. CaCO₃·6H₂O (ikaite; Hesse et al., 1983 ), and nickel, i.e. NiCO₃·5.5H₂O (hellyerite; Bette et al., 2016 ). Our own investigations should elucidate the conditions of formation of the magnesium carbonate hydrates.

2. Experimental

2.1. Synthesis and crystallization

To obtain crystals of MgCO₃·6H₂O suitable for single-crystal diffraction analysis (see V11 in Table S1 of the supporting information), carbon dioxide was bubbled through a suspension of magnesium oxide in deionized water (3.1 g, Magnesia M2329, p.a.) for 22 h at 273.15 K. After that, the solution was filtered and stored without stirring at 273.15 K for 16 d until the product crystallized. The product was filtered off for characterization by powder X-ray diffraction and Raman spectroscopy. For intensity data collection, a prismatic crystal of MgCO₃·6H₂O was recovered from a droplet of its mother liquor and mounted rapidly in the cold (200 K) stream of nitrogen gas of the diffractometer.

2.2. Powder X-ray diffraction

The powder X-ray diffraction (PXRD) patterns were taken for phase identification with a Bruker D8 Discover laboratory powder diffractometer in the Bragg–Brentano set-up (Cu Kα₁ radiation, Vantec 1 detector). The samples were prepared as flat plates and measured at low temperatures (about 273.15 K) with a home-made cooling box (Rincke, 2018).

2.3. Raman spectroscopy

The Raman spectra were recorded shortly after synthesis with a Bruker RFS100/S FT spectrometer at room temperature (Nd/YAG laser, wavelength of the laser = 1064 nm).

2.4. Refinement

Crystal data, data collection and structure refinement details are given in Table 1. The positions of the H atoms could be located from residual electron-density maxima after further refinement and were refined isotropically.

Table 1
Experimental details

Crystal data
Chemical formula	MgCO₃·6H₂O
M_r	192.42
Crystal system, space group	Orthorhombic, Pbam
Temperature (K)	200
a, b, c (Å)	12.3564 (18), 6.5165 (7), 9.9337 (11)
V (Å³)	799.87 (17)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.24
Crystal size (mm)	0.7 × 0.55 × 0.15

Data collection
Diffractometer	Stoe IPDS 2T
Absorption correction	Integration (Coppens, 1970 )
T_min, T_max	0.694, 0.887
No. of measured, independent and observed [I > 2σ(I)] reflections	8319, 1143, 965
R_int	0.036
(sin θ/λ)_max (Å⁻¹)	0.687

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.085, 1.18
No. of reflections	1143
No. of parameters	83
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.23, −0.26
Computer programs: X-AREA (Stoe & Cie, 2015 ), X-RED (Stoe & Cie, 2015), SHELXS97 (Sheldrick, 2008 ), SHELXL2016 (Sheldrick, 2015 ), DIAMOND (Brandenburg, 2017 ) and publCIF (Westrip, 2010 ).

3. Results and discussion

3.1. Conditions of formation and characterization of magnesium carbonate hexahydrate

On the basis of the information of Liu et al. (1990) for the formation of lansfordite, CO₂ was bubbled through aqueous MgO suspensions with various concentrations. After filtration of the solution, the product crystallized at low temperature (273.15–278.15 K), while the CO₂ pressure was decreased by slow degassing of the CO₂ and the solubility product of the carbonate was exceeded. The detailed experimental conditions are given in the supporting information (see Table S1). Characterization of the product with PXRD revealed that nesquehonite is formed at low MgO concentrations, while an unknown phase crystallizes from the solutions at higher Mg²⁺ concentrations, near the solubility of lansfordite at p(CO₂) = 1 bar [m(Mg²⁺) = 0.386 mol kg⁻¹(H₂O) at 273.15 K] (Königsberger et al., 1999; Rincke, 2018). Fig. 1 shows the PXRD pattern of the new product phase in comparison with the reference data for MgCO₃·3H₂O and MgCO₃·5H₂O. The composition of this unknown phase was determined by single-crystal diffraction as MgCO₃·6H₂O. The pentahydrate was not found in our investigations.

Figure 1
Powder XRD pattern of MgCO₃·6H₂O at low temperature (∼273.15 K, Cu Kα radiation) and reference data for MgCO₃·3H₂O (PDF 20-0669) and MgCO₃·5H₂O (PDF 80-1641).

Large prismatic crystals of MgCO₃·6H₂O were obtained while using a longer time of crystallization of 16 d (see V11 in Table S1 of the supporting information). These crystals, which are partly intergrown, convert in a few minutes at room temperature into the typical needles of MgCO₃·3H₂O (Fig. 2). The process of phase transformation could also be seen by means of Raman spectroscopy (Fig. 3). The assignments of the band positions in comparison with the spectra of nesquehonite and lansfordite are given in the supporting information (Table S2).

Figure 2
Microscopic image of prismatic MgCO₃·6H₂O crystals (framed in black) which are partly intergrown. The red-framed crystals are the typical needles of the transformation product MgCO₃·3H₂O.

Figure 3
Raman spectrum of MgCO₃·6H₂O (black) in comparison with the transformation product MgCO₃·3H₂O (red) after storage at room temperature.

3.2. Crystal structure of magnesium carbonate hexahydrate

Magnesium carbonate hexahydrate crystallizes in the orthorhombic space group Pbam (No. 55). The Mg1 atom is located on a twofold axis of symmetry. Atoms C1, O1 and O5, and the water molecule H6A—O6—H6B are positioned on a mirror plane.

Isolated pairs of edge-linked Mg(CO₃)₂(H₂O)₄ octahedra are the main building blocks in the crystal structure (Fig. 4). The crystal structure differs significantly from those of MgCO₃·3H₂O and MgCO₃·5H₂O; MgCO₃·3H₂O exhibits a monoclinic crystal structure consisting of infinite chains along [010], formed by corner-sharing MgO₆ octahedra and CO₃ groups, which link three MgO₆ octahedra by two common corners and one edge (Giester et al., 2000). In the monoclinic crystal structure of MgCO₃·5H₂O, the characteristic building units are isolated octahedra of [Mg(CO₃)₂(H₂O)₄]²⁻ and [Mg(H₂O)₆]²⁺ (Liu et al., 1990).

Figure 4
Illustration of the main building block in the crystal structure of MgCO₃·6H₂O, showing isolated pairs of edge-linked Mg(CO₃)₂(H₂O)₄ octahedra [symmetry codes: (ii) −x + 1, −y, z; (iii) −x + 1, −y, −z + 1; (iv) x, y, −z + 1].

The MgO octahedra in MgCO₃·6H₂O are slightly distorted (Table 2).

Table 2
Selected geometric parameters (Å, °)

Mg1—O1	2.1043 (8)	C1—O4	1.2840 (11)
Mg1—O2	2.0859 (8)	C1—O1	1.2978 (17)
Mg1—O3	2.0672 (8)

O3—Mg1—O2	86.12 (3)	O1—Mg1—O1ⁱⁱ	81.25 (5)
O2—Mg1—O2ⁱ	95.28 (5)	O4—C1—O4ⁱⁱⁱ	120.41 (13)
O3—Mg1—O1	91.46 (4)	O4—C1—O1	119.79 (6)
O2—Mg1—O1	91.74 (3)	Mg1—O1—Mg1ⁱⁱ	98.75 (5)
Symmetry codes: (i) -x+1, -y, z; (ii) -x+1, -y, -z+1; (iii) x, y, -z+1.

The carbonate units are linked in a monodentate manner to two magnesium ions across the O1 atom. They are planar and exhibit C_2v symmetry, because the C1—O1 bond is a little longer than the C1—O4 bond. Furthermore, the O1—C1—O4 angle is a little narrower than the O4—C1—O4^iv angle (see Table 2 for numerical data and symmetry code).

The main building blocks are arranged in a sheet-like pattern, perpendicular to the c axis (Figs. 5a and 5b). Within a sheet, every second main building unit is shifted along the [ $[1 \over 2]$ , $[1 \over 2]$ , 0] direction and rotated by 90°. Consequently, a zigzag-like stacking order results (Fig. 5c). The main building units in a sheet are linked by hydrogen bridging bonds (Fig. 6 and Table 3). The sheets are separated by layers of noncoordinating water molecules in the (001) plane.

Table 3
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H5⋯O2ⁱⁱⁱ	0.812 (18)	2.068 (19)	2.8545 (12)	162.9 (18)
O6—H6B⋯O5ⁱⁱ	0.87 (3)	1.93 (3)	2.7662 (19)	161 (2)
O6—H6A⋯O5^iv	0.76 (3)	1.99 (3)	2.7137 (19)	160 (3)
O3—H3B⋯O4^v	0.788 (19)	2.025 (19)	2.8055 (12)	170.7 (18)
O3—H3A⋯O4^vi	0.93 (2)	1.77 (2)	2.7001 (12)	174.1 (18)
O2—H2B⋯O4ⁱⁱⁱ	0.92 (2)	1.70 (2)	2.5868 (12)	162 (2)
O2—H2A⋯O6	0.84 (2)	1.91 (2)	2.7417 (13)	168.7 (18)
Symmetry codes: (ii) -x+1, -y, -z+1; (iii) x, y, -z+1; (iv) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (v) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (vi) -x+1, -y+1, -z+1.

Figure 5
Projection of the crystal structure of MgCO₃·6H₂O (a) in the a direction, (b) in the b direction and (c) in the c direction.

Figure 6
Part of the crystal structure of MgCO₃·6H₂O, showing the intralayer hydrogen bonds (dashed lines).

All the atoms of the noncoordinating H6A—O6—H6B molecule are located in the (001) plane, whereas in the H5—O5—H5ⁱ molecule, only the O5 atom is situated in this plane (Fig. 7). The (001) plane is also the mirror plane of this molecule. The noncoordinating water molecules are linked by hydrogen bridging bonds both in the (001) plane among themselves and with the MgO octahedra. Thus, the crystal structure is three-dimensional crosslinked (Fig. 7).

Figure 7
Part of the crystal structure of MgCO₃·6H₂O, showing the interlayer hydrogen bonds (dashed lines). The (001) plane is shown in blue.

3.3. Comparison with crystal structures of other carbonate hydrates of bivalent metal ions

Other neutral carbonate hydrates of bivalent metal ions with a water content greater than five units per formula are only known for calcium (CaCO₃·6H₂O) and nickel (NiCO₃·5.5H₂O). Like the title compound, these phases can be synthesized only at low temperatures of about 273.15 K and are transformed at room temperature to CaCO₃ (Coleyshaw et al., 2003 ) and amorphous nickel carbonate (Bette et al., 2016; Rincke, 2018), respectively.

The crystal structure of CaCO₃·6H₂O is significantly different from that of MgCO₃·6H₂O for the very reason that the coordination number of the cation in CaCO₃·6H₂O is eight and not six as in MgCO₃·6H₂O (Dickens & Brown, 1970 ; Hesse et al., 1983).

However, the radii of nickel and magnesium ions are very similar and actually the crystal structures of NiCO₃·5.5H₂O and MgCO₃·6H₂O exhibit similarities. Both crystal structures consist of isolated edge-linked pairs of M(CO₃)(H₂O)₄ (M = Mg or Ni), which are the main building units and are arranged in sheets, together with noncoordinating water molecules, perpendicular to the c axis. The symmetry of NiCO₃·5.5H₂O is lower; it crystallizes in the monoclinic group P2/n. As a consequence, there are two crystallographically different Ni atoms. In contrast to MgCO₃·6H₂O, in NiCO₃·5.5H₂O, the NiO octahedra of Ni2 are not rotated by 90° (Bette et al., 2016).

4. Conclusion

A new neutral magnesium carbonate with the previously unknown high water content of six units per formula, i.e. MgCO₃·6H₂O, was produced by passing gaseous CO₂ through an aqueous suspension of MgO and storing the filtered solution at 273.15 K. The X-ray diffraction pattern and Raman spectra confirmed the formation of the new phase and its transformation to MgCO₃·3H₂O. MgCO₃·5H₂O was not found in our study. Obviously, the formation conditions of magnesium carbonate hydrates depend on the concentration of the MgO suspension, the CO₂ pressure, the temperature regime and the time of storage. Therefore, it would be useful to carry out further systematic investigations on the chemical kinetics of the formation of the magnesium carbonate hydrates.

The crystal structure of MgCO₃·6H₂O differs significantly from the other known magnesium carbonate hydrates, because the main building units are isolated pairs of edge-linked Mg(CO₃)(H₂O)₄ octahedra and free water molecules in the (001) plane, but it exhibits similarities to the nickel salt, NiCO₃·5.5H₂O (hellyerite).

Supporting information

CCDC reference: 1981730

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2053229620001540/lg3251sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2053229620001540/lg3251Isup2.hkl

Experimental conditions and caracterization. DOI: https://doi.org/10.1107/S2053229620001540/lg3251sup3.pdf

Computing details top

Data collection: X-AREA (Stoe & Cie, 2015); cell refinement: X-AREA (Stoe & Cie, 2015); data reduction: X-RED (Stoe & Cie, 2015); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2017); software used to prepare material for publication: publCIF (Westrip, 2010).

Magnesium carbonate hexahysrate top

Crystal data top

MgCO₃·6H₂O	D_x = 1.598 Mg m⁻³
M_r = 192.42	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbam	Cell parameters from 9707 reflections
a = 12.3564 (18) Å	θ = 2.7–27.0°
b = 6.5165 (7) Å	µ = 0.24 mm⁻¹
c = 9.9337 (11) Å	T = 200 K
V = 799.87 (17) Å³	Prism, colorless
Z = 4	0.7 × 0.55 × 0.15 mm
F(000) = 408

Data collection top

Stoe IPDS 2T diffractometer	1143 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	965 reflections with I > 2σ(I)
Plane graphite monochromator	R_int = 0.036
Detector resolution: 6.67 pixels mm^-1	θ_max = 29.2°, θ_min = 3.3°
rotation method scans	h = −16→16
Absorption correction: integration (Coppens, 1970)	k = −7→8
T_min = 0.694, T_max = 0.887	l = −13→11
8319 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.029	All H-atom parameters refined
wR(F²) = 0.085	w = 1/[σ²(F_o²) + (0.0483P)² + 0.1805P] where P = (F_o² + 2F_c²)/3
S = 1.18	(Δ/σ)_max < 0.001
1143 reflections	Δρ_max = 0.23 e Å⁻³
83 parameters	Δρ_min = −0.26 e Å⁻³
0 restraints

Special details top

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 (Å²) top

	x	y	z	U_iso*/U_eq
Mg1	0.500000	0.000000	0.33923 (5)	0.01691 (15)
C1	0.61245 (11)	0.3494 (2)	0.500000	0.0176 (3)
O1	0.55574 (8)	0.18176 (16)	0.500000	0.0189 (2)
O2	0.55982 (7)	0.20756 (12)	0.19775 (8)	0.02241 (19)
O3	0.35722 (6)	0.16456 (13)	0.32879 (9)	0.0230 (2)
O4	0.64098 (6)	0.43100 (12)	0.61217 (8)	0.0228 (2)
O5	0.40386 (10)	0.3240 (2)	1.000000	0.0294 (3)
O6	0.69316 (10)	0.0585 (2)	0.000000	0.0277 (3)
H2A	0.6079 (17)	0.167 (3)	0.1436 (18)	0.039 (5)*
H2B	0.5913 (18)	0.305 (3)	0.252 (3)	0.057 (6)*
H3A	0.3553 (17)	0.302 (3)	0.3545 (18)	0.043 (5)*
H3B	0.2986 (16)	0.124 (3)	0.3454 (16)	0.033 (4)*
H6A	0.755 (2)	0.062 (4)	0.000000	0.039 (7)*
H6B	0.678 (2)	−0.071 (5)	0.000000	0.040 (7)*
H5	0.4421 (17)	0.310 (3)	0.9341 (18)	0.048 (5)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Mg1	0.0166 (2)	0.0156 (3)	0.0185 (2)	−0.00105 (17)	0.000	0.000
C1	0.0141 (6)	0.0140 (6)	0.0246 (6)	0.0010 (5)	0.000	0.000
O1	0.0199 (5)	0.0155 (5)	0.0213 (5)	−0.0044 (4)	0.000	0.000
O2	0.0227 (4)	0.0227 (4)	0.0219 (4)	−0.0016 (3)	0.0023 (3)	0.0024 (3)
O3	0.0174 (4)	0.0188 (4)	0.0328 (4)	0.0004 (3)	0.0011 (3)	−0.0025 (3)
O4	0.0230 (4)	0.0174 (4)	0.0281 (4)	−0.0031 (3)	−0.0031 (3)	−0.0031 (3)
O5	0.0228 (6)	0.0363 (7)	0.0290 (6)	0.0013 (5)	0.000	0.000
O6	0.0220 (6)	0.0280 (6)	0.0331 (6)	−0.0022 (5)	0.000	0.000

Geometric parameters (Å, º) top

Mg1—O1	2.1043 (8)	O3—H3A	0.93 (2)
Mg1—O2	2.0859 (8)	O3—H3B	0.788 (19)
Mg1—O3	2.0672 (8)	O5—H5	0.812 (18)
C1—O4	1.2840 (11)	O5—H5ⁱ	0.812 (18)
C1—O1	1.2978 (17)	O6—H6A	0.76 (3)
O2—H2A	0.84 (2)	O6—H6B	0.87 (3)
O2—H2B	0.92 (2)

O3—Mg1—O2	86.12 (3)	O3ⁱⁱ—Mg1—Mg1ⁱⁱⁱ	92.87 (3)
O2—Mg1—O2ⁱⁱ	95.28 (5)	O3—Mg1—Mg1ⁱⁱⁱ	92.87 (3)
O3—Mg1—O1	91.46 (4)	O2ⁱⁱ—Mg1—Mg1ⁱⁱⁱ	132.36 (3)
O2—Mg1—O1	91.74 (3)	O2—Mg1—Mg1ⁱⁱⁱ	132.36 (3)
O1—Mg1—O1ⁱⁱⁱ	81.25 (5)	O1ⁱⁱⁱ—Mg1—Mg1ⁱⁱⁱ	40.63 (2)
O4—C1—O4^iv	120.41 (13)	O1—Mg1—Mg1ⁱⁱⁱ	40.63 (2)
O4—C1—O1	119.79 (6)	O4^iv—C1—O1	119.79 (6)
Mg1—O1—Mg1ⁱⁱⁱ	98.75 (5)	C1—O1—Mg1ⁱⁱⁱ	130.58 (2)
O3ⁱⁱ—Mg1—O3	174.25 (5)	C1—O1—Mg1	130.58 (2)
O3ⁱⁱ—Mg1—O2ⁱⁱ	86.12 (3)	Mg1—O2—H2A	118.3 (12)
O3—Mg1—O2ⁱⁱ	90.01 (3)	Mg1—O2—H2B	101.9 (14)
O3ⁱⁱ—Mg1—O2	90.01 (3)	H2A—O2—H2B	106.9 (19)
O3ⁱⁱ—Mg1—O1ⁱⁱⁱ	91.46 (4)	Mg1—O3—H3A	120.5 (13)
O3—Mg1—O1ⁱⁱⁱ	92.91 (4)	Mg1—O3—H3B	126.9 (13)
O2ⁱⁱ—Mg1—O1ⁱⁱⁱ	91.74 (3)	H3A—O3—H3B	103.9 (18)
O2—Mg1—O1ⁱⁱⁱ	172.90 (4)	H5—O5—H5ⁱ	107 (3)
O3ⁱⁱ—Mg1—O1	92.91 (4)	H6A—O6—H6B	105 (3)
O2ⁱⁱ—Mg1—O1	172.91 (4)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5···O2^iv	0.812 (18)	2.068 (19)	2.8545 (12)	162.9 (18)
O6—H6B···O5ⁱⁱⁱ	0.87 (3)	1.93 (3)	2.7662 (19)	161 (2)
O6—H6A···O5^v	0.76 (3)	1.99 (3)	2.7137 (19)	160 (3)
O3—H3B···O4^vi	0.788 (19)	2.025 (19)	2.8055 (12)	170.7 (18)
O3—H3A···O4^vii	0.93 (2)	1.77 (2)	2.7001 (12)	174.1 (18)
O2—H2B···O4^iv	0.92 (2)	1.70 (2)	2.5868 (12)	162 (2)
O2—H2A···O6	0.84 (2)	1.91 (2)	2.7417 (13)	168.7 (18)

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

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