The title compound, lithium magnesium chloride heptahydrate, LiCl·MgCl
2·7H
2O, 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(H
2O)
6 octahedra and Li(H
2O)Cl
3 tetrahedra connected by H
Cl hydrogen bonds. The [Li(H
2O)]
+ unit is coordinated by distorted edge-connected Cl
− octahedra.
Supporting information
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.
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.
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).
Lithium magnesium chloride heptahydrate
top
Crystal data top
LiCl·MgCl2·7H2O | Dx = 1.476 Mg m−3 |
Mr = 263.71 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, R3 | Cell parameters from 432 reflections |
Hall symbol: R 3 | θ = 3.1–30.0° |
a = 9.2322 (3) Å | µ = 0.82 mm−1 |
c = 12.0541 (5) Å | T = 293 K |
V = 889.77 (6) Å3 | Rhombohedral, colourless |
Z = 3 | 0.30 × 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 tube | Rint = 0.033 |
Graphite monochromator | θmax = 30.0°, θmin = 3.1° |
ϕ scans, and ω scans | h = −12→12 |
4767 measured reflections | k = −12→12 |
1150 independent reflections | l = −16→16 |
Refinement top
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | All 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 = 1.05 | Δρmax = 0.23 e Å−3 |
1150 reflections | Δρmin = −0.20 e Å−3 |
58 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1 restraint | Extinction coefficient: 0.0105 (10) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983), 572 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: 0.01 (4) |
Crystal data top
LiCl·MgCl2·7H2O | Z = 3 |
Mr = 263.71 | Mo Kα radiation |
Trigonal, R3 | µ = 0.82 mm−1 |
a = 9.2322 (3) Å | T = 293 K |
c = 12.0541 (5) Å | 0.30 × 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 reflections | Rint = 0.033 |
1150 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.016 | All H-atom parameters refined |
wR(F2) = 0.038 | Δρmax = 0.23 e Å−3 |
S = 1.05 | Δρmin = −0.20 e Å−3 |
1150 reflections | Absolute structure: Flack (1983), 572 Friedel pairs |
58 parameters | Absolute 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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
Cl1 | 0.28090 (3) | 0.14521 (3) | 0.50017 (2) | 0.02998 (7) | |
Li1 | 0.0000 | 0.0000 | 0.4348 (2) | 0.0320 (6) | |
Mg1 | 0.3333 | 0.6667 | 0.51437 (4) | 0.02086 (11) | |
O1 | 0.33936 (12) | 0.48624 (11) | 0.61057 (6) | 0.03604 (17) | |
O2 | 0.51991 (10) | 0.67841 (12) | 0.41485 (6) | 0.03345 (16) | |
O3 | 0.0000 | 0.0000 | 0.27800 (13) | 0.0559 (4) | |
H1 | 0.387 (3) | 0.493 (3) | 0.664 (2) | 0.061 (6)* | |
H2 | 0.309 (3) | 0.395 (3) | 0.5826 (16) | 0.049 (4)* | |
H3 | 0.597 (2) | 0.679 (2) | 0.4376 (16) | 0.046 (4)* | |
H4 | 0.543 (2) | 0.712 (2) | 0.3523 (16) | 0.046 (4)* | |
H5 | 0.052 (7) | 0.086 (5) | 0.234 (3) | 0.103 (15)* | 0.67 |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cl1 | 0.03165 (11) | 0.02948 (11) | 0.02796 (10) | 0.01464 (10) | 0.00257 (8) | 0.00054 (7) |
Li1 | 0.0339 (9) | 0.0339 (9) | 0.0281 (12) | 0.0170 (4) | 0.000 | 0.000 |
Mg1 | 0.02171 (16) | 0.02171 (16) | 0.01916 (19) | 0.01085 (8) | 0.000 | 0.000 |
O1 | 0.0527 (5) | 0.0289 (4) | 0.0296 (4) | 0.0227 (3) | −0.0118 (3) | −0.0005 (3) |
O2 | 0.0304 (3) | 0.0503 (5) | 0.0259 (3) | 0.0248 (3) | 0.0044 (3) | 0.0025 (3) |
O3 | 0.0684 (7) | 0.0684 (7) | 0.0307 (7) | 0.0342 (4) | 0.000 | 0.000 |
Geometric parameters (Å, º) top
Cl1—Li1 | 2.3806 (10) | Mg1—O2iii | 2.0569 (7) |
Li1—O3 | 1.890 (3) | Mg1—O2 | 2.0569 (7) |
Li1—Cl1i | 2.3806 (10) | O1—H1 | 0.77 (2) |
Li1—Cl1ii | 2.3806 (10) | O1—H2 | 0.81 (2) |
Mg1—O1iii | 2.0531 (8) | O2—H3 | 0.76 (2) |
Mg1—O1iv | 2.0531 (8) | O2—H4 | 0.803 (19) |
Mg1—O1 | 2.0531 (8) | O3—H5 | 0.87 (4) |
Mg1—O2iv | 2.0569 (7) | | |
| | | |
O3—Li1—Cl1 | 109.34 (7) | O1—Mg1—O2iii | 88.75 (3) |
O3—Li1—Cl1i | 109.34 (7) | O2iv—Mg1—O2iii | 89.42 (3) |
Cl1—Li1—Cl1i | 109.60 (7) | O1iii—Mg1—O2 | 178.17 (4) |
O3—Li1—Cl1ii | 109.34 (7) | O1iv—Mg1—O2 | 88.75 (3) |
Cl1—Li1—Cl1ii | 109.60 (7) | O1—Mg1—O2 | 90.60 (4) |
Cl1i—Li1—Cl1ii | 109.60 (7) | O2iv—Mg1—O2 | 89.42 (3) |
O1iii—Mg1—O1iv | 91.23 (4) | O2iii—Mg1—O2 | 89.42 (3) |
O1iii—Mg1—O1 | 91.23 (4) | Mg1—O1—H1 | 131.0 (17) |
O1iv—Mg1—O1 | 91.23 (4) | Mg1—O1—H2 | 118.1 (13) |
O1iii—Mg1—O2iv | 88.75 (3) | H1—O1—H2 | 109 (2) |
O1iv—Mg1—O2iv | 90.60 (4) | Mg1—O2—H3 | 123.0 (14) |
O1—Mg1—O2iv | 178.17 (4) | Mg1—O2—H4 | 128.1 (12) |
O1iii—Mg1—O2iii | 90.60 (4) | H3—O2—H4 | 106.1 (19) |
O1iv—Mg1—O2iii | 178.17 (4) | Li1—O3—H5 | 127 (2) |
Symmetry codes: (i) −y, x−y, z; (ii) −x+y, −x, z; (iii) −x+y, −x+1, z; (iv) −y+1, x−y+1, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···Cl1v | 0.77 (3) | 2.46 (3) | 3.2156 (10) | 171 (2) |
O1—H2···Cl1 | 0.82 (2) | 2.40 (2) | 3.2056 (9) | 168 (3) |
O2—H3···Cl1vi | 0.76 (2) | 2.43 (2) | 3.1803 (11) | 172.2 (17) |
O2—H4···Cl1vii | 0.803 (19) | 2.382 (19) | 3.1845 (8) | 179 (2) |
O3—H5···Cl1viii | 0.87 (4) | 2.53 (4) | 3.3631 (7) | 160 (4) |
Symmetry codes: (v) −y+2/3, x−y+1/3, z+1/3; (vi) −x+y+1, −x+1, z; (vii) x+1/3, y+2/3, z−1/3; (viii) −x+y+1/3, −x+2/3, z−1/3. |
Experimental details
Crystal data |
Chemical formula | LiCl·MgCl2·7H2O |
Mr | 263.71 |
Crystal system, space group | Trigonal, R3 |
Temperature (K) | 293 |
a, c (Å) | 9.2322 (3), 12.0541 (5) |
V (Å3) | 889.77 (6) |
Z | 3 |
Radiation type | Mo Kα |
µ (mm−1) | 0.82 |
Crystal size (mm) | 0.30 × 0.30 × 0.30 |
|
Data collection |
Diffractometer | Bruker X8 kappa diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4767, 1150, 1134 |
Rint | 0.033 |
(sin θ/λ)max (Å−1) | 0.703 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.016, 0.038, 1.05 |
No. of reflections | 1150 |
No. of parameters | 58 |
No. of restraints | 1 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.23, −0.20 |
Absolute structure | Flack (1983), 572 Friedel pairs |
Absolute structure parameter | 0.01 (4) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···Cl1i | 0.77 (3) | 2.46 (3) | 3.2156 (10) | 171 (2) |
O1—H2···Cl1 | 0.82 (2) | 2.40 (2) | 3.2056 (9) | 168 (3) |
O2—H3···Cl1ii | 0.76 (2) | 2.43 (2) | 3.1803 (11) | 172.2 (17) |
O2—H4···Cl1iii | 0.803 (19) | 2.382 (19) | 3.1845 (8) | 179 (2) |
O3—H5···Cl1iv | 0.87 (4) | 2.53 (4) | 3.3631 (7) | 160 (4) |
Symmetry codes: (i) −y+2/3, x−y+1/3, z+1/3; (ii) −x+y+1, −x+1, z; (iii) x+1/3, y+2/3, z−1/3; (iv) −x+y+1/3, −x+2/3, z−1/3. |
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.