Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl2·nH2O; n = 1, 2, 4)

Sugimoto, K.; Dinnebier, R.E.; Hanson, J.C.

doi:10.1107/S0108768107002558

Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl₂·nH₂O; n = 1, 2, 4)

K. Sugimoto, R. E. Dinnebier and J. C. Hanson

High-quality in situ synchrotron powder diffraction data have been used to investigate the decomposition products of bischofite in the temperature range 298 ≤ T ≤ 873 K. At least eight phases could be identified: MgCl₂·nH₂O (n = 1, 2, 4 and 6), MgOHCl·nH₂O (0 ≤ n ≤ 1.0), MgCl₂ and MgO. The crystal structures of three magnesium chloride hydrates MgCl₂·nH₂O (n = 1, 2, 4) were determined ab initio, replacing published Rietveld refinements from low-quality powder diffraction data based on similarity criteria. MgCl₂·4H₂O was found to be disordered and has been correctly determined for the first time. The crystal structures of bischofite and MgCl₂·4H₂O consist of discrete Mg(H₂O)₆ and MgCl₂(H₂O)₄ octahedra, respectively. The crystal structure of MgCl₂·2H₂O is formed by single chains of edge-sharing MgCl₂(H₂O)₄ octahedra, while in the case of MgCl₂·H₂O double chains of edge-sharing MgCl(H₂O)₅ octahedra are found. The phases in the system MgCl₂–H₂O are intermediates in the technologically important process of MgO and subsequently Mg production. The same phases were recently found to be of key importance in the understanding of cracks in certain magnesia concrete floors.

Keywords: synchrotron powder diffraction; decomposition products; bischofite; chloromagnesite.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768107002558/kd5011sup1.cif Contains datablocks MgCl2-4H2O, MgCl2-2H2O, MgCl2-H2O
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768107002558/kd5011sup2.rtv Contains datablocks MgCl2-4H2O, MgCl2-2H2O, MgCl2-H2O
	Structure factor file (CIF format) https://doi.org/10.1107/S0108768107002558/kd5011sup3.hkl Contains datablocks MgCl2-4H2O, MgCl2-2H2O, MgCl2-H2O

Computing details top

Figures top

(MgCl2-4H2O) Magnesium chloride tetrahydrate top

Crystal data top

Cl₂H₈MgO₄	Z = 2
M_r = 167.27	D_x = 1.638 Mg m⁻³
Orthorhombic, Cmcm	Synchrotron radiation, λ = 0.92187 Å
a = 4.21616 (13) Å	T = 358 K
b = 11.0230 (4) Å	white
c = 7.2951 (3) Å	?, ? × ? × ? mm
V = 339.04 (2) Å³

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.011	? data points
R_wp = 0.019	12 parameters
R_exp = 0.036	H-atom parameters not defined
R(F²) = 0.07832
χ² = NOT FOUND

Crystal data top

Cl₂H₈MgO₄	V = 339.04 (2) Å³
M_r = 167.27	Z = 2
Orthorhombic, Cmcm	Synchrotron radiation, λ = 0.92187 Å
a = 4.21616 (13) Å	T = 358 K
b = 11.0230 (4) Å	?, ? × ? × ? mm
c = 7.2951 (3) Å

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.011	χ² = NOT FOUND
R_wp = 0.019	? data points
R_exp = 0.036	12 parameters
R(F²) = 0.07832	H-atom parameters not defined

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
MG1	0.0	0.5	0.0	0.0535 (13)*	0.5
CL1	0.0	0.3492 (2)	−0.2201 (6)	0.0351 (10)*	0.5
O1	0.5	0.5	0.0	0.0246 (12)*
O2	0.0	0.6432 (5)	−0.1919 (7)	0.0152 (19)*	0.5

Geometric parameters (Å, º) top

MG1—O1ⁱ	2.1081 (1)	MG1—O2^iv	2.746 (5)
MG1—O1	2.1081 (1)	O1—MG1	2.1081 (1)
MG1—CL1	2.311 (4)	O1—MG1^v	2.1081 (1)
MG1—CL1ⁱⁱ	2.633 (4)	CL1—MG1	2.311 (4)
MG1—CL1ⁱⁱⁱ	2.311 (4)	CL1—MG1^vi	2.633 (4)
MG1—CL1^iv	2.633 (4)	CL1—CL1^iv	0.437 (9)
MG1—O2	2.110 (6)	O2—MG1	2.110 (6)
MG1—O2ⁱⁱ	2.746 (5)	O2—MG1^vi	2.746 (5)
MG1—O2ⁱⁱⁱ	2.110 (6)	O2—O2^iv	0.848 (11)

O1ⁱ—MG1—O1	180.0	CL1—MG1—O2ⁱⁱⁱ	85.58 (12)
O1ⁱ—MG1—CL1	90.0	CL1ⁱⁱ—MG1—CL1ⁱⁱⁱ	6.85 (14)
O1ⁱ—MG1—CL1ⁱⁱ	90.0	CL1ⁱⁱ—MG1—CL1^vii	179.9657
O1ⁱ—MG1—CL1ⁱⁱⁱ	90.0	CL1ⁱⁱ—MG1—O2	92.43 (15)
O1ⁱ—MG1—CL1^vii	90.0	CL1ⁱⁱ—MG1—O2ⁱⁱⁱ	87.57 (15)
O1ⁱ—MG1—O2	90.0	CL1ⁱⁱⁱ—MG1—CL1^vii	173.15 (14)
O1ⁱ—MG1—O2ⁱⁱⁱ	90.0	CL1ⁱⁱⁱ—MG1—O2	85.58 (12)
O1—MG1—CL1	90.0	CL1ⁱⁱⁱ—MG1—O2ⁱⁱⁱ	94.42 (12)
O1—MG1—CL1ⁱⁱ	90.0	CL1^vii—MG1—O2	87.57 (15)
O1—MG1—CL1ⁱⁱⁱ	90.0	CL1^vii—MG1—O2ⁱⁱⁱ	92.43 (15)
O1—MG1—CL1^vii	90.0	O2—MG1—O2ⁱⁱⁱ	179.9657
O1—MG1—O2	90.0	MG1—O1—MG1^v	180.0
O1—MG1—O2ⁱⁱⁱ	90.0	MG1—CL1—MG1^vi	94.87 (8)
CL1—MG1—CL1ⁱⁱ	173.15 (14)	MG1—CL1—CL1^vii	134.01 (9)
CL1—MG1—CL1ⁱⁱⁱ	180.0	MG1^vi—CL1—CL1^vii	39.14 (8)
CL1—MG1—CL1^vii	6.85 (14)	MG1—O2—O2^vii	131.57 (13)
CL1—MG1—O2	94.42 (12)

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

(MgCl2-2H2O) Magnesium chloride dihydrate top

Crystal data top

Cl₂H₄MgO₂	V = 229.89 (2) Å³
M_r = 131.24	Z = 2
Monoclinic, C2/m	D_x = 1.896 Mg m⁻³
a = 7.4279 (4) Å	Synchrotron radiation, λ = 0.92187 Å
b = 8.5736 (4) Å	T = 396 K
c = 3.65065 (16) Å	white
β = 98.580 (2)°	?, ? × ? × ? mm

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.010	? data points
R_wp = 0.017	10 parameters
R_exp = 0.036	All H-atom parameters refined
R(F²) = 0.07164
χ² = NOT FOUND

Crystal data top

Cl₂H₄MgO₂	β = 98.580 (2)°
M_r = 131.24	V = 229.89 (2) Å³
Monoclinic, C2/m	Z = 2
a = 7.4279 (4) Å	Synchrotron radiation, λ = 0.92187 Å
b = 8.5736 (4) Å	T = 396 K
c = 3.65065 (16) Å	?, ? × ? × ? mm

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.010	χ² = NOT FOUND
R_wp = 0.017	? data points
R_exp = 0.036	10 parameters
R(F²) = 0.07164	All H-atom parameters refined

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
MG1	0.0	0.0	0.0	0.0329 (13)*
CL1	0.23723 (18)	0.0	0.5588 (4)	0.0393 (9)*
O1	0.0	0.2342 (4)	0.0	0.0310 (11)*
H1	0.10575 (5)	0.3038 (4)	0.023 (6)	0.0312 (14)*

Geometric parameters (Å, º) top

MG1—CL1ⁱ	2.5586 (16)	CL1—MG1^vi	2.5586 (16)
MG1—CL1	2.4887 (14)	CL1—H1^vii	2.448 (12)
MG1—CL1ⁱⁱ	2.4887 (14)	CL1—H1^viii	2.448 (12)
MG1—CL1ⁱⁱⁱ	2.5586 (16)	O1—MG1	2.008 (3)
MG1—O1	2.008 (3)	O1—H1	0.980 (4)
MG1—O1^iv	2.008 (3)	O1—H1ⁱⁱ	0.980 (4)
MG1—H1	2.718 (3)	H1—MG1	2.718 (3)
MG1—H1ⁱⁱ	2.718 (3)	H1—CL1^ix	2.448 (12)
MG1—H1^iv	2.718 (3)	H1—O1	0.980 (4)
MG1—H1^v	2.718 (3)	H1—H1ⁱⁱ	1.555 (3)
CL1—MG1	2.4887 (14)

CL1ⁱ—MG1—CL1	92.64 (4)	CL1ⁱⁱ—MG1—O1	90.0
CL1ⁱ—MG1—CL1ⁱⁱ	87.36 (4)	CL1ⁱⁱ—MG1—O1^iv	90.0
CL1ⁱ—MG1—CL1ⁱⁱⁱ	180.0	CL1ⁱⁱⁱ—MG1—O1	90.0
CL1ⁱ—MG1—O1	90.0	CL1ⁱⁱⁱ—MG1—O1^iv	90.0
CL1ⁱ—MG1—O1^iv	90.0	O1—MG1—O1^iv	180.0
CL1—MG1—CL1ⁱⁱ	179.9802	MG1—CL1—MG1^vi	92.64 (4)
CL1—MG1—CL1ⁱⁱⁱ	87.36 (4)	MG1—O1—H1	127.50 (12)
CL1—MG1—O1	90.0	MG1—O1—H1ⁱⁱ	127.50 (12)
CL1—MG1—O1^iv	90.0	H1—O1—H1ⁱⁱ	105.0 (2)
CL1ⁱⁱ—MG1—CL1ⁱⁱⁱ	92.64 (4)	O1—H1—H1ⁱⁱ	37.50 (12)

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

(MgCl2-H2O) Magnesium chloride monohydrate top

Crystal data top

Cl₂H₂MgO	Z = 4
M_r = 113.23	D_x = 2.022 Mg m⁻³
Orthorhombic, Pnma	Synchrotron radiation, λ = 0.92187 Å
a = 8.9171 (6) Å	T = 434 K
b = 3.63421 (18) Å	white
c = 11.4775 (7) Å	?, ? × ? × ? mm
V = 371.95 (4) Å³

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.009	? data points
R_wp = 0.012	17 parameters
R_exp = 0.037	All H-atom parameters refined
R(F²) = 0.07533
χ² = NOT FOUND

Crystal data top

Cl₂H₂MgO	V = 371.95 (4) Å³
M_r = 113.23	Z = 4
Orthorhombic, Pnma	Synchrotron radiation, λ = 0.92187 Å
a = 8.9171 (6) Å	T = 434 K
b = 3.63421 (18) Å	?, ? × ? × ? mm
c = 11.4775 (7) Å

Data collection top

NSLS X7B
diffractometer system

Refinement top

R_p = 0.009	χ² = NOT FOUND
R_wp = 0.012	? data points
R_exp = 0.037	17 parameters
R(F²) = 0.07533	All H-atom parameters refined

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
MG1	0.1833 (3)	0.25	0.0192 (4)	0.0466 (10)*
CL1	0.3130 (2)	−0.25	−0.0854 (2)	0.0375 (9)*
CL2	0.0341 (3)	0.75	0.12531 (18)	0.0432 (11)*
O1	0.3251 (5)	0.25	0.1449 (4)	0.049 (2)*
H1	0.3038 (8)	0.25	0.2287 (4)	0.054 (3)*
H2	0.4348 (5)	0.25	0.1396 (7)	0.054 (3)*

Geometric parameters (Å, º) top

CL1—MG1ⁱ	2.466 (3)	CL2—MG1^iv	2.561 (3)
CL1—MG1	2.466 (3)	CL2—MG1^v	2.551 (3)
CL1—H1ⁱⁱ	2.374 (4)	O1—MG1	1.918 (5)
CL1—H2ⁱⁱⁱ	2.333 (4)	O1—H1	0.980 (7)
MG1—CL1	2.466 (3)	O1—H2	0.980 (6)
MG1—CL1^iv	2.466 (3)	H1—CL1^vi	2.374 (4)
MG1—CL2ⁱ	2.561 (3)	H1—MG1	2.634 (6)
MG1—CL2	2.561 (3)	H1—O1	0.980 (7)
MG1—CL2^v	2.551 (3)	H1—H2	1.552 (3)
MG1—O1	1.918 (5)	H2—CL1ⁱⁱⁱ	2.333 (4)
MG1—H1	2.634 (6)	H2—MG1	2.634 (6)
MG1—H2	2.634 (6)	H2—O1	0.980 (6)
CL2—MG1	2.561 (3)	H2—H1	1.552 (3)

MG1ⁱ—CL1—MG1	94.93 (14)	CL2ⁱ—MG1—O1	89.13 (15)
CL1—MG1—CL1^iv	94.93 (14)	CL2—MG1—CL2^v	85.08 (12)
CL1—MG1—CL2ⁱ	87.27 (5)	CL2—MG1—O1	89.13 (15)
CL1—MG1—CL2	176.63 (16)	CL2^v—MG1—O1	171.8 (2)
CL1—MG1—CL2^v	92.28 (11)	MG1—CL2—MG1^iv	90.41 (13)
CL1—MG1—O1	93.29 (13)	MG1—CL2—MG1^v	94.92 (12)
CL1^iv—MG1—CL2ⁱ	176.63 (16)	MG1^iv—CL2—MG1^v	94.92 (12)
CL1^iv—MG1—CL2	87.27 (5)	MG1—O1—H1	127.6 (3)
CL1^iv—MG1—CL2^v	92.28 (11)	MG1—O1—H2	127.6 (3)
CL1^iv—MG1—O1	93.29 (13)	H1—O1—H2	104.8 (3)
CL2ⁱ—MG1—CL2	90.41 (13)	O1—H1—H2	37.62 (13)
CL2ⁱ—MG1—CL2^v	85.08 (12)	O1—H2—H1	37.62 (13)

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

Experimental details

	(MgCl2-4H2O)	(MgCl2-2H2O)	(MgCl2-H2O)
Crystal data
Chemical formula	Cl₂H₈MgO₄	Cl₂H₄MgO₂	Cl₂H₂MgO
M_r	167.27	131.24	113.23
Crystal system, space group	Orthorhombic, Cmcm	Monoclinic, C2/m	Orthorhombic, Pnma
Temperature (K)	358	396	434
a, b, c (Å)	4.21616 (13), 11.0230 (4), 7.2951 (3)	7.4279 (4), 8.5736 (4), 3.65065 (16)	8.9171 (6), 3.63421 (18), 11.4775 (7)
α, β, γ (°)	90, 90, 90	90, 98.580 (2), 90	90, 90, 90
V (Å³)	339.04 (2)	229.89 (2)	371.95 (4)
Z	2	2	4
Radiation type	Synchrotron, λ = 0.92187 Å	Synchrotron, λ = 0.92187 Å	Synchrotron, λ = 0.92187 Å
Specimen shape, size (mm)	?, ? × ? × ?	?, ? × ? × ?	?, ? × ? × ?

Data collection
Diffractometer	NSLS X7B diffractometer system	NSLS X7B diffractometer system	NSLS X7B diffractometer system
Specimen mounting	?	?	?
Data collection mode	?	?	?
Scan method	?	?	?
2θ values (°)	2θ_min = ? 2θ_max = ? 2θ_step = ?	2θ_min = ? 2θ_max = ? 2θ_step = ?	2θ_min = ? 2θ_max = ? 2θ_step = ?

Refinement
R factors and goodness of fit	R_p = 0.011, R_wp = 0.019, R_exp = 0.036, R(F²) = 0.07832, χ² = NOT FOUND	R_p = 0.010, R_wp = 0.017, R_exp = 0.036, R(F²) = 0.07164, χ² = NOT FOUND	R_p = 0.009, R_wp = 0.012, R_exp = 0.037, R(F²) = 0.07533, χ² = NOT FOUND
No. of data points	?	?	?
No. of parameters	12	10	17
No. of restraints	?	?	?
H-atom treatment	H-atom parameters not defined	All H-atom parameters refined	All H-atom parameters refined

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Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl₂·nH₂O; n = 1, 2, 4)

Supporting information

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