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A high-pressure phase of magnesium chloride hexa­hydrate (MgCl2·6H2O-II) and its deuterated counterpart (MgCl2·6D2O-II) have been identified for the first time by in-situ single-crystal X-ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single-crystal X-ray diffraction. This high-pressure phase has a similar framework to that in the known ambient-pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen-bond network around the Mg(H2O)6 octa­hedra. These structural features reflect the strain in the high-pressure phases of MgCl2 hydrates.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229619014670/lg3249sup1.cif
Contains datablocks MgCl2_6D2OII, MgCl2_6H2OII, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S2053229619014670/lg3249MgCl2_6D2OIIsup2.hkl
Contains datablock MgCl2_6D2OII

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S2053229619014670/lg3249MgCl2_6H2OIIsup3.hkl
Contains datablock MgCl2_6H2OII

CCDC references: 1962313; 1962314

Computing details top

Program(s) used to refine structure: GSAS for MgCl2_6D2OII; SHELXL2014 (Sheldrick, 2015) for MgCl2_6H2OII.

Magnesium chloride hexadeuterate (MgCl2_6D2OII) top
Crystal data top
[MgCl2(D2O)6]γ = 70.898 (3)°
Mr = 214.89V = 201.36 (1) Å3
Triclinic, P1Z = 1
Hall symbol: -P 1Dx = 1.778 Mg m3
a = 5.89632 (18) ÅNeutron radiation
b = 6.0225 (2) ÅT = 298 K
c = 6.0147 (2) Åcylinder, 6 × 6 mm
α = 86.454 (4)°Specimen preparation: Prepared at 298 K and 0.75 kPa
β = 87.276 (4)°
Data collection top
PLANET (BL11), Materials and Life Science Experimental Facility, J-PARC Tokai, Ibaraki, Japan
diffractometer
Data collection mode: transmission
Radiation source: neutronScan method: time of flight
Specimen mounting: Aluminum cube in six-axis multi anvil press (ATSUHIME)2θfixed = 90.00
Refinement top
Least-squares matrix: fullProfile function: TOF Profile function number 3 with 21 terms Profile coefficients for exponential pseudovoigt convolution Von Dreele, 1990 (unpublished) #1 (alp ) = 0.416418E+24 #2 (bet-0) = 0.017871 #3 (bet-1) = 0.935401 #4 (sig-0) = 0.0 #5 (sig-1 = 521.2 #6 (sig-2) = -1.8 #7 (gam-0) = 0.00 #8 (gam-1) = 21.81 #9 (gam-2) = 0.13 #10 (gsf) = 0.00 #11 (g1ec) = 0.00 #12 (g2ec ) = 0.00 #13 (rstr) = 0.000 #14 (rsta) = 0.000 #15 (rsca) = 0.000 #16 (L11) = 0.000 #17 (L22) = 0.000 #18 (L33) = 0.000 #19 (L12) = 0.000 #20 (L13) = 0.000 #21 (L23) = 0.000 Peak tails are ignored where the intensity is below 0.0020 times the peak Aniso. broadening axis 0.0 0.0 1.0
Rp = 0.02845 parameters
Rwp = 0.03312 restraints
Rexp = 0.012(Δ/σ)max = 0.04
R(F2) = 0.24071Background function: GSAS Background function number 1 with 16 terms. Shifted Chebyshev function of 1st kind 1: 4.716920E-02 2: -5.156720E-03 3: 1.853470E-03 4: 8.037290E-04 5: 1.794140E-03 6: -1.514780E-03 7: -5.851110E-04 8: 1.944230E-03 9: -6.441610E-0410: -5.427010E-0411: -1.207030E-0512: 4.135700E-04 13: -7.124380E-0414: -2.079830E-0415: 1.328750E-0416: -7.306510E-04
3847 data points
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Mg10.00.00.00.012 (3)*
Cl10.3176 (7)0.3184 (7)0.3959 (6)0.0093 (8)*
O10.2561 (17)0.1529 (17)0.8901 (15)0.046 (2)*
O20.1801 (17)0.7103 (19)0.8119 (16)0.046 (2)*
O30.1914 (13)0.8613 (17)0.2790 (16)0.046 (2)*
D1A0.2609 (14)0.2082 (14)0.7463 (16)0.060 (3)*0.960 (8)
D2A0.3400 (16)0.6865 (13)0.7404 (15)0.060 (3)*0.960 (8)
D3A0.2567 (14)0.6918 (17)0.3022 (15)0.060 (3)*0.960 (8)
D3B0.3019 (16)0.9006 (16)0.3519 (16)0.060 (3)*0.960 (8)
D1B0.3004 (15)0.2458 (19)0.9846 (14)0.060 (3)*0.960 (8)
D2B0.0777 (15)0.6741 (15)0.7224 (15)0.060 (3)*0.960 (8)
H1A0.2609 (14)0.2082 (14)0.7463 (16)0.060 (3)*0.040 (8)
H1B0.3004 (15)0.2458 (19)0.9846 (14)0.060 (3)*0.040 (8)
H2A0.3400 (16)0.6865 (13)0.7404 (15)0.060 (3)*0.040 (8)
H2B0.0777 (15)0.6741 (15)0.7225 (15)0.060 (3)*0.040 (8)
H3A0.2567 (14)0.6918 (17)0.3021 (15)0.060 (3)*0.040 (8)
H3B0.3019 (16)0.9006 (16)0.3519 (16)0.060 (3)*0.040 (8)
Geometric parameters (Å, º) top
Mg1—O1i2.075 (9)D1A—O10.910 (9)
Mg1—O1ii2.075 (9)D1A—D1B1.505 (11)
Mg1—O2iii2.090 (10)D1A—H1B1.505 (11)
Mg1—O2iv2.090 (10)D2A—Mg1ix2.759 (8)
Mg1—O3v2.044 (10)D2A—Cl1vii2.134 (10)
Mg1—O3vi2.044 (10)D2A—O20.987 (9)
Mg1—D1Ai2.659 (8)D2A—D2B1.582 (11)
Mg1—D1Aii2.659 (8)D2A—H2B1.582 (11)
Mg1—D2Aiii2.759 (8)D3A—Mg1x2.654 (9)
Mg1—D2Aiv2.759 (8)D3A—Cl12.200 (10)
Mg1—D3Av2.654 (9)D3A—O30.969 (9)
Mg1—D3Avi2.654 (9)D3A—D3B1.420 (12)
Mg1—D3Bv2.741 (9)D3A—H3B1.420 (12)
Mg1—D3Bvi2.741 (9)D3B—Mg1x2.741 (9)
Mg1—D1Bi2.649 (9)D3B—Cl1x2.578 (11)
Mg1—D1Bii2.649 (9)D3B—O30.902 (10)
Mg1—D2Biii2.568 (9)D3B—D3A1.420 (12)
Mg1—D2Biv2.568 (9)D3B—H3A1.420 (12)
Mg1—H1Ai2.659 (8)D1B—Mg1viii2.649 (9)
Mg1—H1Aii2.659 (8)D1B—Cl1viii2.552 (8)
Mg1—H1Bi2.649 (9)D1B—O10.923 (9)
Mg1—H1Bii2.649 (9)D1B—D1A1.505 (11)
Mg1—H2Aiii2.759 (8)D1B—H1A1.505 (11)
Mg1—H2Aiv2.759 (8)D2B—Mg1ix2.568 (9)
Mg1—H2Biii2.568 (9)D2B—Cl1iv2.455 (10)
Mg1—H2Biv2.568 (9)D2B—O20.913 (10)
Mg1—H3Av2.654 (9)D2B—D2A1.582 (11)
Mg1—H3Avi2.654 (9)D2B—H2A1.582 (11)
Mg1—H3Bv2.741 (9)H1A—Mg1viii2.659 (8)
Mg1—H3Bvi2.741 (9)H1A—Cl12.214 (11)
Cl1—D1A2.214 (11)H1A—O10.910 (9)
Cl1—D2Avii2.134 (10)H1A—D1B1.505 (11)
Cl1—D3A2.200 (10)H1A—H1B1.505 (11)
Cl1—D3Bv2.578 (11)H1B—Mg1viii2.649 (9)
Cl1—D1Bi2.552 (8)H1B—Cl1viii2.552 (8)
Cl1—D2Biv2.455 (10)H1B—O10.923 (9)
Cl1—H1A2.214 (11)H1B—D1A1.505 (11)
Cl1—H1Bi2.552 (8)H1B—H1A1.505 (11)
Cl1—H2Avii2.134 (10)H2A—Mg1ix2.759 (8)
Cl1—H2Biv2.455 (10)H2A—Cl1vii2.134 (10)
Cl1—H3A2.200 (10)H2A—O20.987 (9)
Cl1—H3Bv2.578 (11)H2A—D2B1.582 (11)
O1—Mg1viii2.075 (9)H2A—H2B1.582 (11)
O1—D1A0.910 (9)H2B—Mg1ix2.568 (9)
O1—D1B0.923 (9)H2B—Cl1iv2.455 (10)
O1—H1A0.910 (9)H2B—O20.913 (10)
O1—H1B0.923 (9)H2B—D2A1.582 (11)
O2—Mg1ix2.090 (10)H2B—H2A1.582 (11)
O2—D2A0.987 (9)H3A—Mg1x2.654 (9)
O2—D2B0.913 (10)H3A—Cl12.200 (10)
O2—H2A0.987 (9)H3A—O30.969 (9)
O2—H2B0.913 (10)H3A—D3B1.420 (12)
O3—Mg1x2.044 (10)H3A—H3B1.420 (12)
O3—D3A0.969 (9)H3B—Mg1x2.741 (9)
O3—D3B0.902 (10)H3B—Cl1x2.578 (11)
O3—H3A0.969 (9)H3B—O30.902 (10)
O3—H3B0.902 (10)H3B—D3A1.420 (12)
D1A—Mg1viii2.659 (8)H3B—H3A1.420 (12)
D1A—Cl12.214 (11)
O1i—Mg1—O1ii180.0H2A—O2—H2B112.6 (13)
O1i—Mg1—O2iii88.7 (3)Mg1x—O3—D3A119.1 (10)
O1i—Mg1—O2iv91.3 (3)Mg1x—O3—D3B133.1 (12)
O1i—Mg1—O3v90.4 (4)Mg1x—O3—H3A119.1 (10)
O1i—Mg1—O3vi89.6 (4)Mg1x—O3—H3B133.1 (12)
O1ii—Mg1—O2iii91.3 (3)D3A—O3—D3B98.6 (11)
O1ii—Mg1—O2iv88.7 (3)D3A—O3—H3A0.0
O1ii—Mg1—O3v89.6 (4)D3A—O3—H3B98.6 (11)
O1ii—Mg1—O3vi90.4 (4)D3B—O3—H3A98.6 (11)
O2iii—Mg1—O2iv180.0D3B—O3—H3B0.0
O2iii—Mg1—O3v93.7 (4)H3A—O3—H3B98.6 (11)
O2iii—Mg1—O3vi86.3 (4)Cl1—D1A—O1173.3 (11)
O2iv—Mg1—O3v86.3 (4)Cl1—D1A—D1B143.8 (7)
O2iv—Mg1—O3vi93.7 (4)Cl1—D1A—H1B143.8 (7)
O3v—Mg1—O3vi180.0O1—D1A—D1B35.1 (7)
D1A—Cl1—D2Avii123.0 (4)O1—D1A—H1B35.1 (7)
D1A—Cl1—D3A120.1 (4)D1B—D1A—H1B0.0
D1A—Cl1—H1A0.0Cl1vii—D2A—O2171.9 (9)
D1A—Cl1—H2Avii123.0 (4)Cl1—D3A—O3165.7 (10)
D1A—Cl1—H3A120.1 (4)Cl1—D3A—D3B146.3 (7)
D2Avii—Cl1—D3A77.6 (3)Cl1—D3A—H3B146.3 (7)
D2Avii—Cl1—H1A123.0 (4)O3—D3A—D3B38.9 (6)
D2Avii—Cl1—H2Avii0.0O3—D3A—H3B38.9 (6)
D2Avii—Cl1—H3A77.6 (3)D3B—D3A—H3B0.0
D3A—Cl1—H1A120.1 (4)O3—D3B—D3A42.5 (7)
D3A—Cl1—H2Avii77.6 (3)O3—D3B—H3A42.5 (7)
D3A—Cl1—H3A0.0D3A—D3B—H3A0.0
H1A—Cl1—H2Avii123.0 (4)O1—D1B—D1A34.5 (7)
H1A—Cl1—H3A120.1 (4)O1—D1B—H1A34.5 (7)
H2Avii—Cl1—H3A77.6 (3)D1A—D1B—H1A0.0
Mg1viii—O1—D1A120.9 (10)Cl1—H1A—O1173.3 (11)
Mg1viii—O1—D1B119.1 (10)Cl1—H1A—D1B143.8 (7)
Mg1viii—O1—H1A120.9 (10)Cl1—H1A—H1B143.8 (7)
Mg1viii—O1—H1B119.1 (10)O1—H1A—D1B35.1 (7)
D1A—O1—D1B110.4 (13)O1—H1A—H1B35.1 (7)
D1A—O1—H1A0.0D1B—H1A—H1B0.0
D1A—O1—H1B110.4 (13)O1—H1B—D1A34.5 (7)
D1B—O1—H1A110.4 (13)O1—H1B—H1A34.5 (7)
D1B—O1—H1B0.0D1A—H1B—H1A0.0
H1A—O1—H1B110.4 (13)Cl1vii—H2A—O2171.9 (9)
Mg1ix—O2—D2A123.3 (9)Cl1—H3A—O3165.7 (10)
Mg1ix—O2—D2B111.4 (10)Cl1—H3A—D3B146.3 (7)
Mg1ix—O2—H2A123.3 (9)Cl1—H3A—H3B146.3 (7)
Mg1ix—O2—H2B111.4 (10)O3—H3A—D3B38.9 (6)
D2A—O2—D2B112.6 (13)O3—H3A—H3B38.9 (6)
D2A—O2—H2A0.0D3B—H3A—H3B0.0
D2A—O2—H2B112.6 (13)O3—H3B—D3A42.5 (7)
D2B—O2—H2A112.6 (13)O3—H3B—H3A42.5 (7)
D2B—O2—H2B0.0D3A—H3B—H3A0.0
Symmetry codes: (i) x, y, z1; (ii) x, y, z+1; (iii) x, y1, z1; (iv) x, y+1, z+1; (v) x, y1, z; (vi) x, y+1, z; (vii) x+1, y+1, z+1; (viii) x, y, z+1; (ix) x, y+1, z+1; (x) x, y+1, z.
(MgCl2_6H2OII) top
Crystal data top
[MgCl2(H2O)6]Z = 1
Mr = 203.31F(000) = 106
Triclinic, P1Dx = 1.757 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.710700 Å
a = 5.7639 (14) ÅCell parameters from 496 reflections
b = 5.9218 (2) Åθ = 3.4–31.6°
c = 5.9806 (12) ŵ = 0.90 mm1
α = 84.68 (4)°T = 298 K
β = 86.72 (6)°Platelet, colorless
γ = 70.99 (4)°0.13 × 0.13 × 0.06 mm
V = 192.09 (8) Å3
Data collection top
R-AXIS conversion
diffractometer
240 reflections with I > 2σ(I)
Radiation source: Sealed TubeRint = 0.016
Cmf monochromatorθmax = 26.3°, θmin = 3.4°
Detector resolution: 10.0000 pixels mm-1h = 53
dtintegrate.ref scansk = 77
307 measured reflectionsl = 77
240 independent reflections
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullH-atom parameters not defined
R[F2 > 2σ(F2)] = 0.062 w = 1/[σ2(Fo2) + (0.2P)2 + 0.050P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.203(Δ/σ)max = 0.001
S = 1.01Δρmax = 0.29 e Å3
240 reflectionsΔρmin = 0.36 e Å3
18 parameters
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
xyzUiso*/Ueq
Mg10000.0176 (10)*
Cl10.3175 (4)0.3168 (2)0.39389 (18)0.0254 (9)*
O10.2688 (13)0.1537 (7)0.8971 (6)0.0297 (11)*
O20.1914 (13)0.6892 (8)0.8441 (7)0.0313 (12)*
O30.1784 (13)0.8628 (8)0.2884 (7)0.0333 (12)*
Geometric parameters (Å, º) top
Mg—O32.023 (6)Mg—O22.086 (5)
Mg—O3i2.023 (6)O1—Mgiv2.077 (5)
Mg—O1ii2.077 (5)O2—Mgv2.086 (5)
Mg—O12.077 (5)O3—Mgvi2.023 (6)
Mg—O2iii2.086 (5)
O3—Mg—O3i180.0 (3)O1ii—Mg—O2iii91.2 (2)
O3—Mg—O1ii89.9 (2)O1—Mg—O2iii88.8 (2)
O3i—Mg—O1ii90.1 (2)O3—Mg—O290.8 (2)
O3—Mg—O190.1 (2)O3i—Mg—O289.2 (2)
O3i—Mg—O189.9 (2)O1ii—Mg—O288.8 (2)
O1ii—Mg—O1180.00 (18)O1—Mg—O291.2 (2)
O3—Mg—O2iii89.2 (2)O2iii—Mg—O2180.0 (4)
O3i—Mg—O2iii90.8 (2)
Symmetry codes: (i) x, y1, z; (ii) x, y, z1; (iii) x, y1, z1; (iv) x, y, z+1; (v) x, y+1, z+1; (vi) x, y+1, z.
Hydrogen-bond geometry (Å, °) for d-MC6-II at 0.75 GPa top
O—D···AO—DD···AO···AO—D···AH···A*
O1—D1A···Cl0.910 (13)2.213 (10)3.119 (10)173.3 (10)2.242 (3)
O1—D1B···Cli0.924 (14)2.551 (9)3.331 (10)142.4 (10)2.483 (5)
O2—D2A···Clii0.987 (14)2.134 (11)3.115 (11)171.9 (9)2.206 (2)
O2—D2B···Cliii0.913 (14)2.455 (10)3.303 (11)154.7 (10)2.500 (2)
O2—D2B···Cl0.913 (16)2.953 (10)3.431 (12)114.3 (8)2.904 (3)
O3—D3A···Cl0.970 (14)2.200 (10)3.148 (10)165.8 (9)2.206 (2)
O3—D3B···Cliv0.902 (13)2.578 (10)3.203 (10)126.9 (10)2.500 (2)
O3—D3B···Clii0.902 (13)2.686 (10)3.406 (10)137.5 (10)2.904 (3)
Symmetry codes: (i) x, y, z+1; (ii) -x+1, -y+1, -z+1; (iii) -x, -y+1, -z+1; (iv) x, y+1, z.

Note: (*) corresponding interatomic distance in MC6-I (Agron & Busing, 1985).
The geometry of MgO6 octahedron in MC6-I (Agron &amp; Busing, 1985) and MC6-II (this study) top
MC6-IMC6-IId-MC6-II
Pressure (GPa)Ambient1.440.75
Polyhedral volume (Å3)11.6511.6811.79
Average bond length (Å)2.06042.0622.070
Mg—O1 (Å)2.0573 (11)2.077 (8)2.075 (12)
Mg—O2 (Å)2.0620 (14)2.086 (5)2.090 (10)
Mg—O3 (Å)2.023 (5)2.044 (9)
Quadratic elongation1.00041.00061.0017
Distortion index0.001010.012670.00832
Bond-angle variance1.56780.72335.6313
Sample conditionSingle crystalSingle crystalPowder
Radiation sourceNeutronX-rayNeutron
Volumes (Swanson & Peterson 1980), Buer's distortion indices (Baur, 1974), quadratic elongations and bond-angle variances (Robinson et al., 1971) were calculated using the VESTA program (Momma & Izumi, 2011).
 

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