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
CCDC references: 1962313; 1962314
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 = 214.89 | V = 201.36 (1) Å3 |
Triclinic, P1 | Z = 1 |
Hall symbol: -P 1 | Dx = 1.778 Mg m−3 |
a = 5.89632 (18) Å | Neutron radiation |
b = 6.0225 (2) Å | T = 298 K |
c = 6.0147 (2) Å | cylinder, 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: neutron | Scan method: time of flight |
Specimen mounting: Aluminum cube in six-axis multi anvil press (ATSUHIME) | 2θfixed = 90.00 |
Refinement top
Least-squares matrix: full | Profile 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convolution Von Dreele, 1990 (unpublished)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 = 0.028 | 45 parameters |
Rwp = 0.033 | 12 restraints |
Rexp = 0.012 | (Δ/σ)max = 0.04 |
R(F2) = 0.24071 | Background 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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
Mg1 | 0.0 | 0.0 | 0.0 | 0.012 (3)* | |
Cl1 | 0.3176 (7) | 0.3184 (7) | 0.3959 (6) | 0.0093 (8)* | |
O1 | 0.2561 (17) | 0.1529 (17) | 0.8901 (15) | 0.046 (2)* | |
O2 | 0.1801 (17) | 0.7103 (19) | 0.8119 (16) | 0.046 (2)* | |
O3 | 0.1914 (13) | 0.8613 (17) | 0.2790 (16) | 0.046 (2)* | |
D1A | 0.2609 (14) | 0.2082 (14) | 0.7463 (16) | 0.060 (3)* | 0.960 (8) |
D2A | 0.3400 (16) | 0.6865 (13) | 0.7404 (15) | 0.060 (3)* | 0.960 (8) |
D3A | 0.2567 (14) | 0.6918 (17) | 0.3022 (15) | 0.060 (3)* | 0.960 (8) |
D3B | 0.3019 (16) | 0.9006 (16) | 0.3519 (16) | 0.060 (3)* | 0.960 (8) |
D1B | 0.3004 (15) | 0.2458 (19) | 0.9846 (14) | 0.060 (3)* | 0.960 (8) |
D2B | 0.0777 (15) | 0.6741 (15) | 0.7224 (15) | 0.060 (3)* | 0.960 (8) |
H1A | 0.2609 (14) | 0.2082 (14) | 0.7463 (16) | 0.060 (3)* | 0.040 (8) |
H1B | 0.3004 (15) | 0.2458 (19) | 0.9846 (14) | 0.060 (3)* | 0.040 (8) |
H2A | 0.3400 (16) | 0.6865 (13) | 0.7404 (15) | 0.060 (3)* | 0.040 (8) |
H2B | 0.0777 (15) | 0.6741 (15) | 0.7225 (15) | 0.060 (3)* | 0.040 (8) |
H3A | 0.2567 (14) | 0.6918 (17) | 0.3021 (15) | 0.060 (3)* | 0.040 (8) |
H3B | 0.3019 (16) | 0.9006 (16) | 0.3519 (16) | 0.060 (3)* | 0.040 (8) |
Geometric parameters (Å, º) top
Mg1—O1i | 2.075 (9) | D1A—O1 | 0.910 (9) |
Mg1—O1ii | 2.075 (9) | D1A—D1B | 1.505 (11) |
Mg1—O2iii | 2.090 (10) | D1A—H1B | 1.505 (11) |
Mg1—O2iv | 2.090 (10) | D2A—Mg1ix | 2.759 (8) |
Mg1—O3v | 2.044 (10) | D2A—Cl1vii | 2.134 (10) |
Mg1—O3vi | 2.044 (10) | D2A—O2 | 0.987 (9) |
Mg1—D1Ai | 2.659 (8) | D2A—D2B | 1.582 (11) |
Mg1—D1Aii | 2.659 (8) | D2A—H2B | 1.582 (11) |
Mg1—D2Aiii | 2.759 (8) | D3A—Mg1x | 2.654 (9) |
Mg1—D2Aiv | 2.759 (8) | D3A—Cl1 | 2.200 (10) |
Mg1—D3Av | 2.654 (9) | D3A—O3 | 0.969 (9) |
Mg1—D3Avi | 2.654 (9) | D3A—D3B | 1.420 (12) |
Mg1—D3Bv | 2.741 (9) | D3A—H3B | 1.420 (12) |
Mg1—D3Bvi | 2.741 (9) | D3B—Mg1x | 2.741 (9) |
Mg1—D1Bi | 2.649 (9) | D3B—Cl1x | 2.578 (11) |
Mg1—D1Bii | 2.649 (9) | D3B—O3 | 0.902 (10) |
Mg1—D2Biii | 2.568 (9) | D3B—D3A | 1.420 (12) |
Mg1—D2Biv | 2.568 (9) | D3B—H3A | 1.420 (12) |
Mg1—H1Ai | 2.659 (8) | D1B—Mg1viii | 2.649 (9) |
Mg1—H1Aii | 2.659 (8) | D1B—Cl1viii | 2.552 (8) |
Mg1—H1Bi | 2.649 (9) | D1B—O1 | 0.923 (9) |
Mg1—H1Bii | 2.649 (9) | D1B—D1A | 1.505 (11) |
Mg1—H2Aiii | 2.759 (8) | D1B—H1A | 1.505 (11) |
Mg1—H2Aiv | 2.759 (8) | D2B—Mg1ix | 2.568 (9) |
Mg1—H2Biii | 2.568 (9) | D2B—Cl1iv | 2.455 (10) |
Mg1—H2Biv | 2.568 (9) | D2B—O2 | 0.913 (10) |
Mg1—H3Av | 2.654 (9) | D2B—D2A | 1.582 (11) |
Mg1—H3Avi | 2.654 (9) | D2B—H2A | 1.582 (11) |
Mg1—H3Bv | 2.741 (9) | H1A—Mg1viii | 2.659 (8) |
Mg1—H3Bvi | 2.741 (9) | H1A—Cl1 | 2.214 (11) |
Cl1—D1A | 2.214 (11) | H1A—O1 | 0.910 (9) |
Cl1—D2Avii | 2.134 (10) | H1A—D1B | 1.505 (11) |
Cl1—D3A | 2.200 (10) | H1A—H1B | 1.505 (11) |
Cl1—D3Bv | 2.578 (11) | H1B—Mg1viii | 2.649 (9) |
Cl1—D1Bi | 2.552 (8) | H1B—Cl1viii | 2.552 (8) |
Cl1—D2Biv | 2.455 (10) | H1B—O1 | 0.923 (9) |
Cl1—H1A | 2.214 (11) | H1B—D1A | 1.505 (11) |
Cl1—H1Bi | 2.552 (8) | H1B—H1A | 1.505 (11) |
Cl1—H2Avii | 2.134 (10) | H2A—Mg1ix | 2.759 (8) |
Cl1—H2Biv | 2.455 (10) | H2A—Cl1vii | 2.134 (10) |
Cl1—H3A | 2.200 (10) | H2A—O2 | 0.987 (9) |
Cl1—H3Bv | 2.578 (11) | H2A—D2B | 1.582 (11) |
O1—Mg1viii | 2.075 (9) | H2A—H2B | 1.582 (11) |
O1—D1A | 0.910 (9) | H2B—Mg1ix | 2.568 (9) |
O1—D1B | 0.923 (9) | H2B—Cl1iv | 2.455 (10) |
O1—H1A | 0.910 (9) | H2B—O2 | 0.913 (10) |
O1—H1B | 0.923 (9) | H2B—D2A | 1.582 (11) |
O2—Mg1ix | 2.090 (10) | H2B—H2A | 1.582 (11) |
O2—D2A | 0.987 (9) | H3A—Mg1x | 2.654 (9) |
O2—D2B | 0.913 (10) | H3A—Cl1 | 2.200 (10) |
O2—H2A | 0.987 (9) | H3A—O3 | 0.969 (9) |
O2—H2B | 0.913 (10) | H3A—D3B | 1.420 (12) |
O3—Mg1x | 2.044 (10) | H3A—H3B | 1.420 (12) |
O3—D3A | 0.969 (9) | H3B—Mg1x | 2.741 (9) |
O3—D3B | 0.902 (10) | H3B—Cl1x | 2.578 (11) |
O3—H3A | 0.969 (9) | H3B—O3 | 0.902 (10) |
O3—H3B | 0.902 (10) | H3B—D3A | 1.420 (12) |
D1A—Mg1viii | 2.659 (8) | H3B—H3A | 1.420 (12) |
D1A—Cl1 | 2.214 (11) | | |
| | | |
O1i—Mg1—O1ii | 180.0 | H2A—O2—H2B | 112.6 (13) |
O1i—Mg1—O2iii | 88.7 (3) | Mg1x—O3—D3A | 119.1 (10) |
O1i—Mg1—O2iv | 91.3 (3) | Mg1x—O3—D3B | 133.1 (12) |
O1i—Mg1—O3v | 90.4 (4) | Mg1x—O3—H3A | 119.1 (10) |
O1i—Mg1—O3vi | 89.6 (4) | Mg1x—O3—H3B | 133.1 (12) |
O1ii—Mg1—O2iii | 91.3 (3) | D3A—O3—D3B | 98.6 (11) |
O1ii—Mg1—O2iv | 88.7 (3) | D3A—O3—H3A | 0.0 |
O1ii—Mg1—O3v | 89.6 (4) | D3A—O3—H3B | 98.6 (11) |
O1ii—Mg1—O3vi | 90.4 (4) | D3B—O3—H3A | 98.6 (11) |
O2iii—Mg1—O2iv | 180.0 | D3B—O3—H3B | 0.0 |
O2iii—Mg1—O3v | 93.7 (4) | H3A—O3—H3B | 98.6 (11) |
O2iii—Mg1—O3vi | 86.3 (4) | Cl1—D1A—O1 | 173.3 (11) |
O2iv—Mg1—O3v | 86.3 (4) | Cl1—D1A—D1B | 143.8 (7) |
O2iv—Mg1—O3vi | 93.7 (4) | Cl1—D1A—H1B | 143.8 (7) |
O3v—Mg1—O3vi | 180.0 | O1—D1A—D1B | 35.1 (7) |
D1A—Cl1—D2Avii | 123.0 (4) | O1—D1A—H1B | 35.1 (7) |
D1A—Cl1—D3A | 120.1 (4) | D1B—D1A—H1B | 0.0 |
D1A—Cl1—H1A | 0.0 | Cl1vii—D2A—O2 | 171.9 (9) |
D1A—Cl1—H2Avii | 123.0 (4) | Cl1—D3A—O3 | 165.7 (10) |
D1A—Cl1—H3A | 120.1 (4) | Cl1—D3A—D3B | 146.3 (7) |
D2Avii—Cl1—D3A | 77.6 (3) | Cl1—D3A—H3B | 146.3 (7) |
D2Avii—Cl1—H1A | 123.0 (4) | O3—D3A—D3B | 38.9 (6) |
D2Avii—Cl1—H2Avii | 0.0 | O3—D3A—H3B | 38.9 (6) |
D2Avii—Cl1—H3A | 77.6 (3) | D3B—D3A—H3B | 0.0 |
D3A—Cl1—H1A | 120.1 (4) | O3—D3B—D3A | 42.5 (7) |
D3A—Cl1—H2Avii | 77.6 (3) | O3—D3B—H3A | 42.5 (7) |
D3A—Cl1—H3A | 0.0 | D3A—D3B—H3A | 0.0 |
H1A—Cl1—H2Avii | 123.0 (4) | O1—D1B—D1A | 34.5 (7) |
H1A—Cl1—H3A | 120.1 (4) | O1—D1B—H1A | 34.5 (7) |
H2Avii—Cl1—H3A | 77.6 (3) | D1A—D1B—H1A | 0.0 |
Mg1viii—O1—D1A | 120.9 (10) | Cl1—H1A—O1 | 173.3 (11) |
Mg1viii—O1—D1B | 119.1 (10) | Cl1—H1A—D1B | 143.8 (7) |
Mg1viii—O1—H1A | 120.9 (10) | Cl1—H1A—H1B | 143.8 (7) |
Mg1viii—O1—H1B | 119.1 (10) | O1—H1A—D1B | 35.1 (7) |
D1A—O1—D1B | 110.4 (13) | O1—H1A—H1B | 35.1 (7) |
D1A—O1—H1A | 0.0 | D1B—H1A—H1B | 0.0 |
D1A—O1—H1B | 110.4 (13) | O1—H1B—D1A | 34.5 (7) |
D1B—O1—H1A | 110.4 (13) | O1—H1B—H1A | 34.5 (7) |
D1B—O1—H1B | 0.0 | D1A—H1B—H1A | 0.0 |
H1A—O1—H1B | 110.4 (13) | Cl1vii—H2A—O2 | 171.9 (9) |
Mg1ix—O2—D2A | 123.3 (9) | Cl1—H3A—O3 | 165.7 (10) |
Mg1ix—O2—D2B | 111.4 (10) | Cl1—H3A—D3B | 146.3 (7) |
Mg1ix—O2—H2A | 123.3 (9) | Cl1—H3A—H3B | 146.3 (7) |
Mg1ix—O2—H2B | 111.4 (10) | O3—H3A—D3B | 38.9 (6) |
D2A—O2—D2B | 112.6 (13) | O3—H3A—H3B | 38.9 (6) |
D2A—O2—H2A | 0.0 | D3B—H3A—H3B | 0.0 |
D2A—O2—H2B | 112.6 (13) | O3—H3B—D3A | 42.5 (7) |
D2B—O2—H2A | 112.6 (13) | O3—H3B—H3A | 42.5 (7) |
D2B—O2—H2B | 0.0 | D3A—H3B—H3A | 0.0 |
Symmetry codes: (i) x, y, z−1; (ii) −x, −y, −z+1; (iii) x, y−1, z−1; (iv) −x, −y+1, −z+1; (v) x, y−1, 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. |
Crystal data top
[MgCl2(H2O)6] | Z = 1 |
Mr = 203.31 | F(000) = 106 |
Triclinic, P1 | Dx = 1.757 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.710700 Å |
a = 5.7639 (14) Å | Cell parameters from 496 reflections |
b = 5.9218 (2) Å | θ = 3.4–31.6° |
c = 5.9806 (12) Å | µ = 0.90 mm−1 |
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 Tube | Rint = 0.016 |
Cmf monochromator | θmax = 26.3°, θmin = 3.4° |
Detector resolution: 10.0000 pixels mm-1 | h = −5→3 |
dtintegrate.ref scans | k = −7→7 |
307 measured reflections | l = −7→7 |
240 independent reflections | |
Refinement top
Refinement on F2 | 0 restraints |
Least-squares matrix: full | H-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 = 1.01 | Δρmax = 0.29 e Å−3 |
240 reflections | Δρmin = −0.36 e Å−3 |
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 | x | y | z | Uiso*/Ueq | |
Mg1 | 0 | 0 | 0 | 0.0176 (10)* | |
Cl1 | 0.3175 (4) | 0.3168 (2) | 0.39389 (18) | 0.0254 (9)* | |
O1 | 0.2688 (13) | 0.1537 (7) | 0.8971 (6) | 0.0297 (11)* | |
O2 | 0.1914 (13) | 0.6892 (8) | 0.8441 (7) | 0.0313 (12)* | |
O3 | 0.1784 (13) | 0.8628 (8) | 0.2884 (7) | 0.0333 (12)* | |
Geometric parameters (Å, º) top
Mg—O3 | 2.023 (6) | Mg—O2 | 2.086 (5) |
Mg—O3i | 2.023 (6) | O1—Mgiv | 2.077 (5) |
Mg—O1ii | 2.077 (5) | O2—Mgv | 2.086 (5) |
Mg—O1 | 2.077 (5) | O3—Mgvi | 2.023 (6) |
Mg—O2iii | 2.086 (5) | | |
| | | |
O3—Mg—O3i | 180.0 (3) | O1ii—Mg—O2iii | 91.2 (2) |
O3—Mg—O1ii | 89.9 (2) | O1—Mg—O2iii | 88.8 (2) |
O3i—Mg—O1ii | 90.1 (2) | O3—Mg—O2 | 90.8 (2) |
O3—Mg—O1 | 90.1 (2) | O3i—Mg—O2 | 89.2 (2) |
O3i—Mg—O1 | 89.9 (2) | O1ii—Mg—O2 | 88.8 (2) |
O1ii—Mg—O1 | 180.00 (18) | O1—Mg—O2 | 91.2 (2) |
O3—Mg—O2iii | 89.2 (2) | O2iii—Mg—O2 | 180.0 (4) |
O3i—Mg—O2iii | 90.8 (2) | | |
Symmetry codes: (i) x, y−1, z; (ii) x, y, z−1; (iii) x, y−1, z−1; (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 topO—D···A | O—D | D···A | O···A | O—D···A | H···A* |
O1—D1A···Cl | 0.910 (13) | 2.213 (10) | 3.119 (10) | 173.3 (10) | 2.242 (3) |
O1—D1B···Cli | 0.924 (14) | 2.551 (9) | 3.331 (10) | 142.4 (10) | 2.483 (5) |
O2—D2A···Clii | 0.987 (14) | 2.134 (11) | 3.115 (11) | 171.9 (9) | 2.206 (2) |
O2—D2B···Cliii | 0.913 (14) | 2.455 (10) | 3.303 (11) | 154.7 (10) | 2.500 (2) |
O2—D2B···Cl | 0.913 (16) | 2.953 (10) | 3.431 (12) | 114.3 (8) | 2.904 (3) |
O3—D3A···Cl | 0.970 (14) | 2.200 (10) | 3.148 (10) | 165.8 (9) | 2.206 (2) |
O3—D3B···Cliv | 0.902 (13) | 2.578 (10) | 3.203 (10) | 126.9 (10) | 2.500 (2) |
O3—D3B···Clii | 0.902 (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 & Busing, 1985) and
MC6-II (this study) top | MC6-I | MC6-II | d-MC6-II |
Pressure (GPa) | Ambient | 1.44 | 0.75 |
Polyhedral volume (Å3) | 11.65 | 11.68 | 11.79 |
Average bond length (Å) | 2.0604 | 2.062 | 2.070 |
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 elongation | 1.0004 | 1.0006 | 1.0017 |
Distortion index | 0.00101 | 0.01267 | 0.00832 |
Bond-angle variance | 1.5678 | 0.7233 | 5.6313 |
Sample condition | Single crystal | Single crystal | Powder |
Radiation source | Neutron | X-ray | Neutron |
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). |