Determination of the crystal structure of magnesium perchlorate hydrates by X-ray powder diffraction and the charge-flipping method

X-ray powder diffraction (XRD) data were used to solve the crystal structures of phases in the magnesium perchlorate hydrate system, Mg(ClO₄)₂·nH₂O (n = 4, 2). A heating stage and humidity generator interfaced to an environmental cell enabled in-situ XRD analyses of dehydration reactions under controlled temperatures and partial pressures of H₂O (P). The crystal structures were determined using an ab initio charge-flipping method and were refined using fundamental-parameter Rietveld methods. Dehydration of magnesium perchlorate hexahydrate to tetrahydrate (348 K) results in a decrease in symmetry (space group = C2), where isolated Mg²⁺ cations are equatorially coordinated by four H₂O molecules with two [ClO₄]⁻ tetrahedra at the apices. Further dehydration to the dihydrate (423 K) leads to bridging of the isolated packets to form double corner-sharing chains of octahedra and polyhedra (space group = C2/m).

Computing details

(profile1)

Crystal data

Cl2H8MgO12	V = 504.56 (4) Å^3
Mr = 295.27	Z = 2
Monoclinic, C2	Cu Kα radiation, λ = 1.5418 Å
a = 11.4806 (4) Å	T = 348 K
b = 8.0025 (3) Å	white
c = 5.9370 (3) Å	flat sheet, 10 × 14 mm
β = 112.328 (3)°

Data collection

Bruker D8 diffractometer	Scan method: step
Specimen mounting: Ni-Cr plated copper front loaded sample mount	2θmin = 10°, 2θmax = 110°, 2θstep = 0.017°
Data collection mode: reflection

Refinement

Rp = 0.074	Profile function: PVII
Rwp = 0.104	52 parameters
Rexp = 0.006	H-atom parameters not refined
RBragg = 0.058	Background function: third-order Chebyshev polynomial
8383 data points	Preferred orientation correction: sixth-order spherical harmonics
Excluded region(s): 89.5 to 90.5 2θ

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

	x	y	z	Biso*/Beq
Cl	0.70333	1	0.10907	0.4
Mg	1	1	0.5	0.8
O1	0.333333	0.5	0.166667	1.2
O2	0.166667	0.66083	0.15301	1.2
O3	0.833333	0.37593	0.76325	1.2
O4	0.5	0.23849	0.5	1.2
O5	1	0.27036	0.5	1.2
O6	0.65143	0.97079	0.85351	1.2
O7	0.89363	1.01313	0.72724	1.2
H1	0.54733	0.8735	0.56476	1
H2	0.93783	0.65429	0.43875	1
H3	0.5796	0.50118	0.09709	1
H4	0.30059	0.50382	0.71989	1

(profile2)

Crystal data

Cl2H4MgO10	V = 387.89 (3) Å^3
Mr = 259.24	Z = 2
Monoclinic, C2/m	Cu Kα radiation, λ = 1.5418 Å
a = 14.3878 (6) Å	T = 423 K
b = 5.21861 (19) Å	white
c = 5.4380 (3) Å	flat sheet, 10 × 14 mm
β = 108.199 (2)°

Data collection

Bruker D8 diffractometer	Scan method: step
Specimen mounting: Ni-Cr plated copper front loaded sample mount	2θmin = 10°, 2θmax = 110°, 2θstep = 0.017°
Data collection mode: reflection

Refinement

Rp = 0.053	Profile function: PVII
Rwp = 0.078	25 parameters
Rexp = 0.012	H-atom parameters not refined
RBragg = 0.036	Background function: third-order Chebyshev polynomial
8383 data points	Preferred orientation correction: sixth-order spherical harmonics
Excluded region(s): 89.5 to 90.5 2θ

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

	x	y	z	Biso*/Beq
Mg	0	0	0.5	0.8
Cl	0.62578	1	0.83043	0.4
O1	0.38167	0.5	0.64837	1.2
O2	0.32043	1	0.89	1.2
O3	0.05762	0.25	0.79317	1.2
O4	0.31265	1	0.34525	1.2
H	0.67187	0.62617	0.43766	1