Revision of the Mg(ClO₄)₂·4H₂O crystal structure

A revision is presented of the restrained Rietveld analysis of the crystal structure of magnesium perchlorate tetrahydrate, Mg(ClO₄)₂·4H₂O, recently published by Robertson & Bish [(2010), Acta Cryst. B66, 579-584]. The actual symmetry of the material is shown to be C2/m. The corrected structure model is refined by the derivative difference method [Solovyov (2004). J. Appl. Cryst. 37, 743-749], anisotropically for all non-H atoms and isotropically for two independent H atoms without restraints.

Computing details

Program(s) used to refine structure: DDM.

(I)

Crystal data

Cl2H8MgO12	V = 504.46 (3) Å^3
Mr = 295.26	Z = 2
Monoclinic, C2/m	Dx = 1.945 Mg m^−3
Hall symbol: -C 2Y	Cu Kα radiation, λ = 1.5406, 1.5444 Å
a = 11.4802 (2) Å	T = 348 K
b = 8.0016 (4) Å	white
c = 5.9363 (2) Å	flat_sheet, 10 × 14 mm
β = 112.3169 (8)°

Data collection

Specimen mounting: Ni-Cr plated copper front-loaded sample mount	Scan method: step
Data collection mode: reflection	2θmin = 10.000°, 2θmax = 85.000°, 2θstep = 0.017°

Refinement

Least-squares matrix: full	4417 data points
Rwp = 0.055	76 parameters
Rexp = 0.016	0 restraints
RBragg = 0.011	(Δ/σ)max = 0.005
R(F) = 0.020

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl	0.2974 (2)	0.00000	0.3935 (5)	0.0373
Mg	0.00000	0.00000	0.00000	0.0255
O1	0.1627 (3)	0.00000	0.3207 (6)	0.0461
O2	0.3321 (2)	0.1458 (3)	0.3056 (6)	0.1046
O3	0.3507 (3)	0.00000	0.6526 (8)	0.0696
O4	0.00000	0.2513 (5)	0.00000	0.0566
O5	−0.1013 (4)	0.00000	0.2218 (9)	0.0567
H1	0.036 (5)	0.312 (4)	0.121 (6)	0.095 (15)*
H2	−0.124 (2)	−0.099 (4)	0.222 (6)	0.079 (17)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl	0.023 (2)	0.042 (2)	0.046 (3)	0.0000	0.0127 (19)	0.0000
Mg	0.025 (2)	0.037 (3)	0.018 (3)	0.0000	0.0116 (19)	0.0000
O1	0.014 (4)	0.099 (4)	0.021 (4)	0.0000	0.001 (3)	0.0000
O2	0.102 (4)	0.091 (2)	0.138 (4)	−0.033 (2)	0.064 (3)	0.040 (2)
O3	0.049 (5)	0.092 (4)	0.036 (4)	0.0000	−0.021 (3)	0.0000
O4	0.078 (6)	0.033 (5)	0.047 (4)	0.0000	0.010 (5)	0.0000
O5	0.054 (4)	0.090 (6)	0.045 (3)	0.0000	0.041 (2)	0.0000

Geometric parameters (Å, º)

Cl—O1	1.440 (4)	Mg—O4	2.011 (4)
Cl—O2	1.397 (4)	Mg—O5	2.061 (6)
Cl—O3	1.423 (5)	O4—H1	0.83 (3)
Mg—O1	2.100 (3)	O5—H2	0.83 (3)
O1—Cl—O2	108.34 (15)	O1—Mg—O5^ii	93.22 (14)
O1—Cl—O3	107.2 (3)	Mg—O4—H1	126 (2)
O2—Cl—O2^i	113.3 (4)	H1—O4—H1^ii	109 (4)
O2—Cl—O3	109.72 (17)	Mg—O5—H2	104 (3)
O1—Mg—O5	86.78 (14)	H2—O5—H2^i	144 (4)

Symmetry codes: (i) x, −y, z; (ii) −x, y, −z.