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The title compound, lithium magnesium chloride hepta­hydrate, LiCl·MgCl2·7H2O, was analyzed in 1988 by powder X-ray diffraction [Emons, Brand, Pohl & Köhnke (1988). Z. Anorg. Allg. Chem. 563, 180–184] and a monoclinic crystal lattice was determined. In the present work, the structure was solved from single-crystal diffraction data. A trigonal structure was found, exhibiting a network structure of Mg(H2O)6 octa­hedra and Li(H2O)Cl3 tetra­hedra connected by H...Cl hydrogen bonds. The [Li(H2O)]+ unit is coordinated by distorted edge-connected Cl octa­hedra.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109029448/fn3030sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270109029448/fn3030Isup2.hkl
Contains datablock I

Comment top

LiCl.MgCl2.7H2O belongs to the group of double salts MX.MgX2.6H2O with M equal to Li(H2O)+, K+, Rb+, Cs+, NH4+ and H3O+, and X equal to Cl-, Br- and I-. The most important member of this group is the mineral carnallite, KCl.MgCl2.6H2O. Carnallite is formed during evaporation of potassium and magnesium rich waters. It belongs to the natural salts and represents a source for potash fertilizer production and the recovery of magnesium chloride.

The structure analysis of LiCl.MgCl2.7H2O is motivated by a growing interest in natural lithium resources for battery materials. Lithium carnallite is formed during evaporation of brines from salt lakes in South America.

In order to study the crystal chemistry of MX.MgX2.6H2O compounds, Emons et al. (1988) performed powder diffraction experiments on all of the above-mentioned carnallites, except (H3O)X.MgX2.6H2O. Crystal structures were determined for KCl.MgCl2.6H2O (Fischer, 1973; Schlemper et al., 1985), NH4Cl.MgCl2.6H2O (Nakayasu, 1983; Solans et al., 1983; Marsh, 1992b), RbCl.MgCl2.6H2O (Waizumi, Masuda, Ohtaki, Burkov & Scripkin, 1991; Marsh, 1992a), CsCl.MgCl2.6H2O (Waizumi, Masuda & Ohtaki, 1991), and RbBr.MgBr2.6H2O and CsBr.MgBr2.6H2O (Dinnebier et al., 2008).

The structure of LiCl.MgCl2.7H2O consists, as shown in Fig. 1, basically of Mg(H2O)6 octahedra and Li(H2O)Cl3 pseudo-tetrahedra. The dumpbell-shaped Li(H2O)+ unit is oriented with the bonding axis parallel to the threefold symmetry axis. Consequently, the Li(H2O)Cl3 tetrahedron consists of three symmetry equivalent Cl- and H+ positions, where the two H atoms of the water molecule occupy statistically three energetically equivalent positions. Typical for MX.MgX2.6H2O structures, but not necessarily expected for LiCl.MgCl2.7H2O, is the octahedral coordination of M by Cl-. Considering the Li(H2O)+ unit as coordination center, a distorted Li(H2O)Cl6 octahedra results, as presented in Fig. 2. A combination of three Li···Cl bonds of 2.3806 (10) Å and three H···Cl hydrogen bonds of 2.52 (5) Å length leads to an edge-connected three-dimensional network of Li(H2O)Cl6 octahedra, which is stabilized by hydrogen-bonded Mg(H2O)6 octahedra. A main reason for the trigonal lattice, as shown for the unit cell in Fig. 3, can be seen in the trigonal symmetry of the Li(H2O) dumbbell (Fig. 2). Despite its trigonal structure, LiCl.MgCl2.7H2O is structurally related to a cubic lattice. In the rhombohedral setting of the unit cell, the lattice parameters are a = 6.675 Å and α = 87.51°. This nearly cubic atomic arrangement is obvious from Fig. 4.

Related literature top

For related literature, see: Dinnebier et al. (2008); Emons et al. (1988); Fischer (1973); Marsh (1992, 1992); Nakayasu (1983); Schlemper et al. (1985); Solans et al. (1983); Waizumi, Masuda & Ohtaki (1991); Waizumi, Masuda, Ohtaki, Burkov & Scripkin (1991).

Experimental top

LiCl.MgCl2.7H2O was prepared by cooling a solution of MgCl2.6H2O (23.4 g) and LiCl (14.9 g) in deionized water (17.6 g) from 345 to 303 K within a period of 3 d. This was carried out in closed test tubes with constant rotation of the bubbler in a climatic chamber (Vötsch VC4043). To prevent contact of the air humidity with the crystals they were covered by n-hexane. A crystal of 0.3 × 0.3 × 0.3 mm was selected and embedded in a two-compound adhesive-based epoxy resin (UHU plus sofortfest) before being mounted on the single-crystal diffractometer.

Refinement top

A structure solution using direct methods and a refinement of the atomic positions with respect to the isotropic displacement parameters led to the positions of the Mg, O and Cl atoms. The positions of the H and Li atoms could be located from residual electron-density maxima after further refinement. The site occupancy of the H atom belonging to O3 (Fig. 1) refined to a value of 2/3, indicating that two H atoms share three equivalent positions.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: APEX2 (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures top
[Figure 1] Fig. 1. The asymmetric unit and symmetry-related atoms of LiCl.MgCl2.7H2O. Displacement ellipsoids are drawn at the 50% probability level. H atoms are not labeled. [Symmetry codes: (i) -y, x - y, z; (ii) -x + y, -x, z; (iii) -y + 1, x - y + 1, z; (iv) -x + y, -x + 1, z.]
[Figure 2] Fig. 2. The octahedral coordination of the Li(H2O)+ unit by Cl-.
[Figure 3] Fig. 3. A projection along the [001] direction of a trigonal unit cell of LiCl.MgCl2.7H2O.
[Figure 4] Fig. 4. A projection showing the rhombohedral and nearly cubic framework of the lithium carnallite structure.
Lithium magnesium chloride heptahydrate top
Crystal data top
LiCl·MgCl2·7H2ODx = 1.476 Mg m3
Mr = 263.71Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3Cell parameters from 432 reflections
Hall symbol: R 3θ = 3.1–30.0°
a = 9.2322 (3) ŵ = 0.82 mm1
c = 12.0541 (5) ÅT = 293 K
V = 889.77 (6) Å3Rhombohedral, colourless
Z = 30.30 × 0.30 × 0.30 mm
F(000) = 408
Data collection top
Bruker X8 kappa
diffractometer
1134 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.033
Graphite monochromatorθmax = 30.0°, θmin = 3.1°
ϕ scans, and ω scansh = 1212
4767 measured reflectionsk = 1212
1150 independent reflectionsl = 1616
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.016 w = 1/[σ2(Fo2) + (0.0256P)2 + 0.0237P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.038(Δ/σ)max < 0.001
S = 1.05Δρmax = 0.23 e Å3
1150 reflectionsΔρmin = 0.20 e Å3
58 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
1 restraintExtinction coefficient: 0.0105 (10)
Primary atom site location: structure-invariant direct methodsAbsolute structure: Flack (1983), 572 Friedel pairs
Secondary atom site location: difference Fourier mapAbsolute structure parameter: 0.01 (4)
Crystal data top
LiCl·MgCl2·7H2OZ = 3
Mr = 263.71Mo Kα radiation
Trigonal, R3µ = 0.82 mm1
a = 9.2322 (3) ÅT = 293 K
c = 12.0541 (5) Å0.30 × 0.30 × 0.30 mm
V = 889.77 (6) Å3
Data collection top
Bruker X8 kappa
diffractometer
1134 reflections with I > 2σ(I)
4767 measured reflectionsRint = 0.033
1150 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.016All H-atom parameters refined
wR(F2) = 0.038Δρmax = 0.23 e Å3
S = 1.05Δρmin = 0.20 e Å3
1150 reflectionsAbsolute structure: Flack (1983), 572 Friedel pairs
58 parametersAbsolute structure parameter: 0.01 (4)
1 restraint
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Cl10.28090 (3)0.14521 (3)0.50017 (2)0.02998 (7)
Li10.00000.00000.4348 (2)0.0320 (6)
Mg10.33330.66670.51437 (4)0.02086 (11)
O10.33936 (12)0.48624 (11)0.61057 (6)0.03604 (17)
O20.51991 (10)0.67841 (12)0.41485 (6)0.03345 (16)
O30.00000.00000.27800 (13)0.0559 (4)
H10.387 (3)0.493 (3)0.664 (2)0.061 (6)*
H20.309 (3)0.395 (3)0.5826 (16)0.049 (4)*
H30.597 (2)0.679 (2)0.4376 (16)0.046 (4)*
H40.543 (2)0.712 (2)0.3523 (16)0.046 (4)*
H50.052 (7)0.086 (5)0.234 (3)0.103 (15)*0.67
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.03165 (11)0.02948 (11)0.02796 (10)0.01464 (10)0.00257 (8)0.00054 (7)
Li10.0339 (9)0.0339 (9)0.0281 (12)0.0170 (4)0.0000.000
Mg10.02171 (16)0.02171 (16)0.01916 (19)0.01085 (8)0.0000.000
O10.0527 (5)0.0289 (4)0.0296 (4)0.0227 (3)0.0118 (3)0.0005 (3)
O20.0304 (3)0.0503 (5)0.0259 (3)0.0248 (3)0.0044 (3)0.0025 (3)
O30.0684 (7)0.0684 (7)0.0307 (7)0.0342 (4)0.0000.000
Geometric parameters (Å, º) top
Cl1—Li12.3806 (10)Mg1—O2iii2.0569 (7)
Li1—O31.890 (3)Mg1—O22.0569 (7)
Li1—Cl1i2.3806 (10)O1—H10.77 (2)
Li1—Cl1ii2.3806 (10)O1—H20.81 (2)
Mg1—O1iii2.0531 (8)O2—H30.76 (2)
Mg1—O1iv2.0531 (8)O2—H40.803 (19)
Mg1—O12.0531 (8)O3—H50.87 (4)
Mg1—O2iv2.0569 (7)
O3—Li1—Cl1109.34 (7)O1—Mg1—O2iii88.75 (3)
O3—Li1—Cl1i109.34 (7)O2iv—Mg1—O2iii89.42 (3)
Cl1—Li1—Cl1i109.60 (7)O1iii—Mg1—O2178.17 (4)
O3—Li1—Cl1ii109.34 (7)O1iv—Mg1—O288.75 (3)
Cl1—Li1—Cl1ii109.60 (7)O1—Mg1—O290.60 (4)
Cl1i—Li1—Cl1ii109.60 (7)O2iv—Mg1—O289.42 (3)
O1iii—Mg1—O1iv91.23 (4)O2iii—Mg1—O289.42 (3)
O1iii—Mg1—O191.23 (4)Mg1—O1—H1131.0 (17)
O1iv—Mg1—O191.23 (4)Mg1—O1—H2118.1 (13)
O1iii—Mg1—O2iv88.75 (3)H1—O1—H2109 (2)
O1iv—Mg1—O2iv90.60 (4)Mg1—O2—H3123.0 (14)
O1—Mg1—O2iv178.17 (4)Mg1—O2—H4128.1 (12)
O1iii—Mg1—O2iii90.60 (4)H3—O2—H4106.1 (19)
O1iv—Mg1—O2iii178.17 (4)Li1—O3—H5127 (2)
Symmetry codes: (i) y, xy, z; (ii) x+y, x, z; (iii) x+y, x+1, z; (iv) y+1, xy+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···Cl1v0.77 (3)2.46 (3)3.2156 (10)171 (2)
O1—H2···Cl10.82 (2)2.40 (2)3.2056 (9)168 (3)
O2—H3···Cl1vi0.76 (2)2.43 (2)3.1803 (11)172.2 (17)
O2—H4···Cl1vii0.803 (19)2.382 (19)3.1845 (8)179 (2)
O3—H5···Cl1viii0.87 (4)2.53 (4)3.3631 (7)160 (4)
Symmetry codes: (v) y+2/3, xy+1/3, z+1/3; (vi) x+y+1, x+1, z; (vii) x+1/3, y+2/3, z1/3; (viii) x+y+1/3, x+2/3, z1/3.

Experimental details

Crystal data
Chemical formulaLiCl·MgCl2·7H2O
Mr263.71
Crystal system, space groupTrigonal, R3
Temperature (K)293
a, c (Å)9.2322 (3), 12.0541 (5)
V3)889.77 (6)
Z3
Radiation typeMo Kα
µ (mm1)0.82
Crystal size (mm)0.30 × 0.30 × 0.30
Data collection
DiffractometerBruker X8 kappa
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
4767, 1150, 1134
Rint0.033
(sin θ/λ)max1)0.703
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.016, 0.038, 1.05
No. of reflections1150
No. of parameters58
No. of restraints1
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.23, 0.20
Absolute structureFlack (1983), 572 Friedel pairs
Absolute structure parameter0.01 (4)

Computer programs: APEX2 (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···Cl1i0.77 (3)2.46 (3)3.2156 (10)171 (2)
O1—H2···Cl10.82 (2)2.40 (2)3.2056 (9)168 (3)
O2—H3···Cl1ii0.76 (2)2.43 (2)3.1803 (11)172.2 (17)
O2—H4···Cl1iii0.803 (19)2.382 (19)3.1845 (8)179 (2)
O3—H5···Cl1iv0.87 (4)2.53 (4)3.3631 (7)160 (4)
Symmetry codes: (i) y+2/3, xy+1/3, z+1/3; (ii) x+y+1, x+1, z; (iii) x+1/3, y+2/3, z1/3; (iv) x+y+1/3, x+2/3, z1/3.
 

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