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Acta Cryst. (2013). E69, i25    [ doi:10.1107/S1600536813008416 ]

Dilithium hexa­hydroxidostannate(IV) dihydrate, a second monoclinic modification with a layer structure

S. Kamaha and H. Reuter

Abstract top

The title compound, Li2[Sn(OH)6]·2H2O, is dimorphic. As for the previously described [alpha]-modification, the title [beta]-modification crystallizes in the monoclinic system and contains the same primary building units, viz [Sn(OH)6]2- octa­hedra and [Li([mu]2-OH)3(H2O)] tetra­hedra. In contrast to the Sn-O bond lengths that are very similar in both modifications, the Li-O bond lengths differ significantly, in particular those involving the water mol­ecule. In the new [beta]-modification, the primary building units are linked into layers parallel to (010). The [Sn(OH)6]2- octa­hedra (-1 symmetry) form hexa­gonal nets and the [Li([mu]2-OH)3(H2O)] tetra­hedra are situated in between, with their apices in an alternating fashion up and down. O-H...O hydrogen bonds between OH groups and water mol­ecules exist within the layers as well as between them.

Comment top

Compounds of the hexahydroxidostannate(IV) anion, [Sn(OH)6]2-, are well defined in chemistry as well as in mineralogy. In combination with bivalent cations, the anion is found in some rare tin minerals of natural and anthropogenic (Basciano et al., 1998) origin like schoenfliesite, Mg[Sn(OH)]6, the prototype and name giver for a large group of isostructural compounds of composition M[Sn(OH)6] with M = Mg, Fe, Mn, Zn and Ca (Strunz & Nickel, 2001). Corresponding compounds of univalent cations are of general formula M2[Sn(OH)]6 or exist as hydrates, M2[Sn(OH)6].nH2O. The anhydrous compounds of sodium and potassium are long known and commercially available products (preparing salt, M = Na) used in dye industry. Their structures have been determined recently (Jacobs & Stahl, 2000). Only from lithium, the structures of the anhydrous compound (Yang et al., 2001) as well as that of the dihydrate (Reuter & Bargon, 1997) are known. The last one crystallizes in the monoclinic space group P21/n with [Sn(OH)6]2- octahedra and [Li(µ2-OH)3(H2O)] tetrahedra linked in a three-dimensional way. By changing the crystallization conditions, we were able to isolate a new modification (in the following called β) of the dihydrate. This polymorph likewise crystallizes in the same space group and consists of the same building units as the known modification (in the following called α), but these primary units are linked two-dimensionally.

The asymmetric unit of the title compound (Fig. 1) consists of half a formula unit with the tin atom at a crystallographic centre of symmetry [Wyckoff letter 2b], and with all other atoms in general positions. Within the centrosymmetric hexahydroxidostannate(IV) anion, [Sn(OH)6]2-, the Sn—O bond lengths range from 2.0567 (11) to 2.0699 (11) Å [mean value: 2.064 (7) Å] and the O—Sn—O bond angles from 86.92 (4)° to 93.08 (4)° and are comparable with the corresponding values in the α-modification [d(Sn—O) = 2.053 (1) - 2.075 (1), mean value 2.060 (13) Å; O—Sn—O = 87.21 (4)° - 92.79 (4)°]. The lithium ion is tetrahedrally coordinated by three hydroxyl groups of three different hexahydroxidostannate(IV) anions and by one water molecule to form a [Li(µ2-OH)3(H2O)] unit. The Li—OHhydroxyl bond lengths are in the range from 1.948 (3) Å to 1.965 (3) Å, mean value 1.958 (9) Å, whereas the bond to the water molecule is somewhat longer [2.030 (3) Å]. Although similar in constitution with the coordination polyhedron of Li in the α-modification, the Li—O bond lengths in the β-modification differ significantly. In the α-modification the Li—OHhydroxyl bond lengths cover a larger range [1.932 (2) Å - 1.987 (2) Å] whereas the Li—H2O bond is considerably shorter [1.946 (3) Å].

In contrast to the previous modification, where [Sn(OH)6]-octahedra and [Li(OH)3(H2O)]-tetrahedra are linked three-dimensionally, they form in the new modification a two-dimensional layer structure (Fig. 2) parallel to (010). Within the almost planar layers, the [Sn(OH)6]-octahedra build up a hexagonal net with the tetrahedra in between, very similar to the situation of octahedral and tetrahedral voids in a close-packed layer. In summary, each octahedron is surrounded by six tetrahedra, with their apices in an alternating fashion up and down (Fig. 3).

In addition to the strong covalent and electrostatic interactions between cations, anions and water molecules, hydrogen bonds (Fig. 4) are important and fall into two categories: hydrogen bonds within the layers and those between the layers. The first ones are dominated by the water molecules that are coplanar with the layer plane and act as donors of two hydrogen bonds to two OH-groups of two different neighboring octahedra as well as acceptors of a hydrogen bond of an hydroxyl group of a third octahedron. The water molecules are also involved in the interlayer hydrogen bonds as acceptors resulting in an overall trigonal-bipyramidal coordination mode at the oxygen atom of the water molecule.

Related literature top

For background to the structures of M2[Sn(OH)6] with M = Na, K, see: Jacobs & Stahl (2000). For literature on Li2[Sn(OH)6].nH2O, see: Reuter & Bargon (1997) for n = 2; Yang et al. (2001) for n = 0. For M[Sn(OH)6] compounds (M = divalent metal), see: Strunz & Nickel (2001); Basciano et al. (1998).

Experimental top

In a typical experiment, equimolar amounts of freshly prepared K2[Sn(OH)6] and LiNO3 were dissolved as far as possible in 15 ml H2O2 (15%wt). Undissolved reagents were removed by centrifugation before the solvent was allowed to evaporate slowly. Compact, colorless single crystals of the title compound were formed during some weeks.

Refinement top

Hydrogen atoms were clearly identified in difference Fourier syntheses. Their positions were refined with respect to a common O—H distance of 0.96 Å and for the water molecule an H—O—H angle of 104.9° before they were fixed and allowed to ride on the corresponding oxygen atoms. One common isotropic displacement factor was refined for all H-atoms.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Combined polyhedra and ball-and-stick models of the coordination spheres around tin and lithium with the atomic numbering scheme used; with exception of the hydrogen atoms, which are shown as spheres with common isotropic radius, all other atoms are represented with their anisotropic displacement ellipsoids at the 50% probability level; additional bonds to neighboring metal atoms are indicated as shortened sticks.
[Figure 2] Fig. 2. Combined polyhedra (around Sn) and ball-and-stick (around Li) model of the layered structure of the title compound viewed down [001].
[Figure 3] Fig. 3. Arrangement of [Sn(OH)6] octahedra and [Li(OH)3(H2O)] tetrahedra within the almost planar layers of the title compound; top view looking down the b-axes at the head, side view looking down [110] at the bottom.
[Figure 4] Fig. 4. Details of the hydrogen bonding system in the crystal structure of the title compound the hydrogen and oxygen atoms of the [Li(OH)3(H2O)]-tetrahedron are involved in; with exception of the hydrogen atoms, which are shown as spheres with common isotropic radius, all other atoms are represented with their anisotropic displacement ellipsoids at the 50% probability level; hydrogen bonds indicated as red dashed, additional bonds as shortened sticks. [Symmetry codes: (1) 1 - x,1 - y, -z; (2) 1 + x, y, z; (3) 1 - x, -0.5 + y, 0.5 - z; (4) 1 - x, 1 - y, 1 - z.]
Dilithium hexahydroxidostannate(IV) dihydrate top
Crystal data top
Li2[Sn(OH)6]·2H2OF(000) = 260
Mr = 270.65Dx = 2.661 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 9252 reflections
a = 6.1028 (2) Åθ = 3.8–33.2°
b = 10.4708 (3) ŵ = 3.78 mm1
c = 6.0003 (2) ÅT = 100 K
β = 118.249 (1)°Block, colourless
V = 337.76 (2) Å30.15 × 0.14 × 0.11 mm
Z = 2
Data collection top
986 independent reflections
Radiation source: fine-focus sealed tube964 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.024
phi and ω scansθmax = 30.0°, θmin = 3.8°
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
h = 88
Tmin = 0.601, Tmax = 0.681k = 1414
11484 measured reflectionsl = 88
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.013H-atom parameters constrained
wR(F2) = 0.032 w = 1/[σ2(Fo2) + (0.0111P)2 + 0.5571P]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max < 0.001
986 reflectionsΔρmax = 0.36 e Å3
54 parametersΔρmin = 0.39 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0094 (10)
Crystal data top
Li2[Sn(OH)6]·2H2OV = 337.76 (2) Å3
Mr = 270.65Z = 2
Monoclinic, P21/cMo Kα radiation
a = 6.1028 (2) ŵ = 3.78 mm1
b = 10.4708 (3) ÅT = 100 K
c = 6.0003 (2) Å0.15 × 0.14 × 0.11 mm
β = 118.249 (1)°
Data collection top
986 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2009)
964 reflections with I > 2σ(I)
Tmin = 0.601, Tmax = 0.681Rint = 0.024
11484 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0130 restraints
wR(F2) = 0.032H-atom parameters constrained
S = 1.09Δρmax = 0.36 e Å3
986 reflectionsΔρmin = 0.39 e Å3
54 parameters
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. A suitable single-crystal was selected under a polarization microscope and mounted on a 50 µm MicroMesh MiTeGen MicromountTM using FROMBLIN Y perfluoropolyether (LVAC 16/6, Aldrich).

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
Sn10.50000.50000.50000.00669 (7)
O10.5924 (2)0.61350 (11)0.2773 (2)0.0092 (2)
H10.43440.62080.12780.045 (4)*
O20.2930 (2)0.38228 (11)0.1944 (2)0.0092 (2)
H20.34380.29470.20610.045 (4)*
O30.1780 (2)0.60408 (11)0.3926 (2)0.0088 (2)
H30.19650.69300.36590.045 (4)*
Li10.8284 (5)0.5657 (3)0.1561 (6)0.0123 (5)
O40.8497 (2)0.37229 (11)0.1795 (2)0.0101 (2)
H410.86430.37710.34580.045 (4)*
H421.01750.36510.20710.045 (4)*
Atomic displacement parameters (Å2) top
Sn10.00660 (8)0.00674 (9)0.00670 (9)0.00001 (4)0.00314 (6)0.00009 (5)
O10.0091 (5)0.0103 (5)0.0081 (5)0.0009 (4)0.0039 (4)0.0007 (4)
O20.0096 (5)0.0088 (5)0.0084 (5)0.0005 (4)0.0035 (4)0.0003 (4)
O30.0085 (5)0.0075 (5)0.0107 (5)0.0006 (4)0.0047 (4)0.0006 (4)
Li10.0136 (12)0.0121 (13)0.0117 (13)0.0001 (10)0.0063 (11)0.0006 (10)
O40.0094 (5)0.0116 (5)0.0096 (5)0.0002 (4)0.0048 (4)0.0004 (4)
Geometric parameters (Å, º) top
Sn1—O1i2.0567 (11)O2—H20.9600
Sn1—O12.0567 (11)O3—Li1iii1.965 (3)
Sn1—O3i2.0654 (11)O3—H30.9600
Sn1—O32.0654 (11)Li1—O2ii1.948 (3)
Sn1—O2i2.0699 (11)Li1—O3iv1.965 (3)
Sn1—O22.0699 (11)Li1—O42.030 (3)
O1—Li11.961 (3)O4—H410.9600
O2—Li1ii1.948 (3)
O1i—Sn1—O3i90.31 (4)Li1ii—O2—Sn1123.42 (11)
O1—Sn1—O3i89.69 (4)Li1ii—O2—H2106.9
O1i—Sn1—O389.69 (4)Sn1—O2—H2117.6
O1—Sn1—O390.31 (4)Li1iii—O3—Sn1131.67 (10)
O1i—Sn1—O2i90.49 (4)Sn1—O3—H3113.2
O1—Sn1—O2i89.51 (4)O2ii—Li1—O1110.99 (15)
O3i—Sn1—O2i86.92 (4)O2ii—Li1—O3iv116.79 (15)
O3—Sn1—O2i93.08 (4)O1—Li1—O3iv114.65 (15)
O1i—Sn1—O289.51 (4)O2ii—Li1—O4109.44 (15)
O1—Sn1—O290.49 (4)O1—Li1—O4105.27 (14)
O3i—Sn1—O293.08 (4)O3iv—Li1—O498.16 (13)
O3—Sn1—O286.92 (4)Li1—O4—H4189.5
Li1—O1—Sn1124.68 (10)H41—O4—H42105.0
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1, y+1, z; (iii) x1, y, z; (iv) x+1, y, z.
Hydrogen-bond geometry (Å, º) top
O1—H1···O4ii0.961.842.7955 (16)173
O2—H2···O1v0.961.932.8853 (16)173
O3—H3···O4vi0.961.902.8343 (16)164
O4—H41···O3i0.961.722.6634 (16)167
O4—H42···O2iv0.961.732.6662 (16)165
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1, y+1, z; (iv) x+1, y, z; (v) x+1, y1/2, z+1/2; (vi) x+1, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaLi2[Sn(OH)6]·2H2O
Crystal system, space groupMonoclinic, P21/c
Temperature (K)100
a, b, c (Å)6.1028 (2), 10.4708 (3), 6.0003 (2)
β (°) 118.249 (1)
V3)337.76 (2)
Radiation typeMo Kα
µ (mm1)3.78
Crystal size (mm)0.15 × 0.14 × 0.11
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan
(SADABS; Bruker, 2009)
Tmin, Tmax0.601, 0.681
No. of measured, independent and
observed [I > 2σ(I)] reflections
11484, 986, 964
(sin θ/λ)max1)0.703
R[F2 > 2σ(F2)], wR(F2), S 0.013, 0.032, 1.09
No. of reflections986
No. of parameters54
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.36, 0.39

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006) and Mercury (Macrae et al., 2008), SHELXTL (Sheldrick, 2008).

Selected bond lengths (Å) top
Sn1—O12.0567 (11)O2—Li1i1.948 (3)
Sn1—O32.0654 (11)O3—Li1ii1.965 (3)
Sn1—O22.0699 (11)Li1—O42.030 (3)
O1—Li11.961 (3)
Symmetry codes: (i) x+1, y+1, z; (ii) x1, y, z.
Hydrogen-bond geometry (Å, º) top
O1—H1···O4i0.961.842.7955 (16)173.2
O2—H2···O1iii0.961.932.8853 (16)173.4
O3—H3···O4iv0.961.902.8343 (16)164.0
O4—H41···O3v0.961.722.6634 (16)167.2
O4—H42···O2vi0.961.732.6662 (16)164.8
Symmetry codes: (i) x+1, y+1, z; (iii) x+1, y1/2, z+1/2; (iv) x+1, y+1/2, z+1/2; (v) x+1, y+1, z+1; (vi) x+1, y, z.