Tin(IV) sulfate dihydrate comprises of (100) layers of [SnO4(H2O)2] octahedra corner-connected by sulfate tetrahedra, and with O—H⋯O hydrogen-bonding between the layers.
Keywords: tin(IV) sulfate dihydrate, crystal structures, Sn(IV), powder diffraction
Abstract
Tin(IV) sulfate dihydrate, Sn(SO4)2·2H2O, was prepared in a reflux of sulfuric acid under oxidizing conditions. Its crystal structure was determined from powder synchrotron X-ray diffraction data and is constructed of (100) layers of [SnO4(H2O)2] octahedra (point group symmetry 1) corner-connected by sulfate tetrahedra. Hydrogen bonds of moderate strength between the water molecules and sulfate O atoms hold the layers together.
Structure description
Tin sulfates and derivated compounds display an interesting structural chemistry. A number of tin sulfates, including an oxide sulfate, were reported by Ahmed et al. (1998 ▸) based on synthesis in 50–95%wt H2SO4 at and above room temperature. In addition to the earlier reported and reasonably characterized compounds of SnIISO4 (Rentzeperis, 1962 ▸), SnII2OSO4 (Lundren et al., 1982 ▸), SnII3O(OH)2SO4 (Grimvall, 1975 ▸; Davies et al., 1975 ▸), SnII6O4(SO4)(OH)2 (Locock et al., 2006 ▸) and Sn7(OH)12(SO4)2 (SnII6SnIV(OH)12(SO4)2; Grimvall, 1982 ▸), the high-temperature reactions in concentrated sulfuric acid revealed the existence of two polymorphs of Sn(SO4)2·2H2O (A and B), the tetrahydrate Sn(SO4)2·4H2O, the mixed-valent SnII/SnIV oxide sulfate Sn6O(SO4)9 and two polymorphs of anhydrous Sn(SO4)2, of which one is obtained on heating to around 773 K (Ahmed et al., 1998 ▸). Since all the SnIV-containing compounds are highly hygroscopic, handling and characterization require inert conditions. Loss of crystallinity was rapidly observed for samples subjected to air at ambient conditions. More recently, SnIV(SO4)2 and mixed-valent SnIISnIV(SO4)3 were reported (Hämmer et al., 2021 ▸). The former adopts a crystal structure with [SnO6] octahedra corner-connected through sulfate tetrahedra in all directions, while the latter adopts a layered structure.
We report here on the crystal structure of one of the above mentioned compounds, Sn(SO4)2·2H2O (B), for which Ahmed et al. (1998 ▸) suggested a monoclinic structure with a = 9.705 (1) Å, b = 5.652 (1) Å, c = 7.033 (1) Å, β = 106.86 (1)o based on powder X-ray diffraction data. On heating, Sn(SO4)2·2H2O (B) transforms into anhydrous Sn(SO4)2 at about 623 K.
The crystal structure of Sn(SO4)2·2H2O is shown in Figs. 1 ▸ and 2 ▸, and selected bond lengths and angles are given in Table 1 ▸. The structure can be described as being constructed of layers of slightly distorted [SnO4(H2O)2] octahedra corner-connected by sulfate tetrahedra. There is no bonding directly between the [SnO4(H2O)2] units. The layers extend parallel to (100) and are stacked along [100], Fig. 1 ▸. The SnIV atom is situated at an inversion centre (multiplicity 2, Wyckoff letter b) and is surrounded by four sulfate groups that connect the [SnO4(H2O)2] units, and by two water molecules. Considering the Sn—O bond lengths, we find them to be in excellent agreement for SnIV with bond lengths from 1.968 (6) to 2.046 (6) Å (Table 1 ▸). In comparison, bond lengths of 2.016 (3) – 2.049 (3) Å are observed for SnIV(SO4)2 by Hämmer et al. (2021 ▸). The two water molecules (O5) are directed towards the inter-layer space and exhibit the longest of the Sn—O bonds. The sulfate group shows a slight scatter in the S—O bond lengths, between 1.465 (6) and 1.526 (6) Å, around the ideal bond length of ∼1.49 Å (Louisnathan et al., 1977 ▸). Some deviations in the lengths are expected due to the different local environments of the sulfate group as two of its oxygen atoms are directed toward Sn, while the other two are directed toward hydrogen atoms.
Figure 1.
Crystal structure of Sn(SO4)2·2H2O in a view along [010]. Purple coordination polyhedra represent [SnO4(H2O)2] octahedra, and the yellow polyhedra the sulfate tetrahedra. Dashed lines indicate hydrogen bonds.
Figure 2.
Crystal structure of Sn(SO4)2·2H2O in a view along [100]. Colour code is as in Fig. 1 ▸.
Table 1. Selected geometric parameters (Å, °).
| Sn1—O1 | 1.968 (6) | S1—O2 | 1.465 (6) |
| Sn1—O4i | 2.042 (5) | S1—O3 | 1.467 (6) |
| Sn1—O5 | 2.046 (6) | S1—O4 | 1.495 (5) |
| S1—O1 | 1.526 (6) | ||
| H1—O5—H2 | 103.2 (6) |
Symmetry code: (i) 
.
Intra-and interlayer O—H⋯O hydrogen bonding between water molecules and sulfate O atoms is observed. The intralayer hydrogen bond is rather strong [O5⋯O2ii = 2.541 (8) Å], whereas the interlayer hydrogen bond, which is responsible for the cohesion of the layers along [100], is of moderate strength [O5⋯O3ii = 2.735 (7) Å]. Other numerical values for these interactions are compiled in Table 2 ▸.
Table 2. Hydrogen-bond geometry (Å, °).
| D—H⋯A | D—H | H⋯A | D⋯A | D—H⋯A |
|---|---|---|---|---|
| O5—H1⋯O2ii | 0.969 (6) | 1.574 (5) | 2.541 (8) | 175.6 (4) |
| O5—H2⋯O3iii | 0.963 (6) | 1.780 (4) | 2.735 (7) | 171.0 (4) |
Symmetry codes: (ii) 
; (iii) 
.
Synthesis and crystallization
The current sample of Sn(SO4)2·2H2O (B) was obtained according to Ahmed et al. (1998 ▸), by reacting Sn powder (Fluka; 99.9%) in 85%wt H2SO4 at 368 K in reflux while oxygen gas was passed through the reaction mixture. The obtained product was isolated after ten days by decanting, followed by washing and drying before storage in a vacuum desiccator.
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. Synchrotron X-ray data of an Sn(SO4)2·2H2O powder sample was collected in a 0.5 mm capillary at BM01B at the Swiss–Norwegian beamlines (SNBL), the European Synchrotron Radiation Facility (ESRF), Grenoble, France, with a wavelength of 1.00098 Å using a high-resolution detector. The data revealed the Sn(SO4)2·2H2O sample to be of high purity, with two minor impurity reflections visible at about 1 and 2.05 Å−1 (Fig. 3 ▸). The indexed cell given by Ahmed et al. (1998 ▸) was used as a starting point for the structure solution. For the final refinement, the a and c axes were interchanged relative to the setting used by Ahmed et al. (1998 ▸). Le Bail refinements with the reported lattice parameters yielded a good fit, and space group P21/c as the space group. Charge flipping using SUPERFLIP (Palatinus & Chapuis, 2007 ▸) implemented in JANA2006 (Petříček et al., 2014) quickly gave a good model for the atomic positions for the heavier elements. Without the constraint for the S—O bond length, unrealistically large variations were obtained. The ideal bond length for the S—O bond in a sulfate group is ∼1.49 Å (Louisnathan et al., 1977 ▸). The crystal structure was refined with distance restraints on the S—O bond length by selecting the target distance to 1.49 Å, a value of 0.002 Å for allowed deviations, and a moderate penalty factor.
Table 3. Experimental details.
| Crystal data | |
| Chemical formula | Sn(SO4)2·2H2O |
| M r | 346.86 |
| Crystal system, space group | Monoclinic, P21/c |
| Temperature (K) | 293 |
| a, b, c (Å) | 7.03475 (5), 5.65165 (5), 9.70464 (7) |
| β (°) | 106.8524 (4) |
| V (Å3) | 369.27 (1) |
| Z | 2 |
| Radiation type | Synchrotron, λ = 1.00098 Å |
| μ (mm−1) | 10.46 |
| Specimen shape, size (mm) | Cylinder, 40 × 0.5 |
| Data collection | |
| Diffractometer | High-resolution sychrotron |
| Specimen mounting | Capillary |
| Data collection mode | Transmission |
| Scan method | Step |
| 2θ values (°) | 2θmin = 8.207 2θmax = 53, 2θstep = 0.007 |
| Refinement | |
| R factors and goodness of fit | Rp = 0.024, Rwp = 0.033, Rexp = 0.017, R(F) = 0.045, χ2 = 3.792 |
| No. of parameters | 46 |
| No. of restraints | 4 |
| H-atom treatment | H-atom parameters constrained |
Figure 3.
Observed (black), calculated (red), and difference (blue) intensity profile from Rietveld refinement of synchrotron X-ray data for Sn(SO4)2·2H2O. Bragg reflections are marked with green bars.
Based on a previous report regarding composition and charge neutrality (Ahmed et al., 1998 ▸), we added hydrogen atoms to the structure. They were placed to have an O—H bond length of ∼0.95 Å and with an angle of ∼105° between the H atoms. The H atoms were further directed towards O2 and O3 as the lengths to these oxygen atoms indicate hydrogen bonding (Table 2 ▸). Displacement parameters were not refined for hydrogen atoms. Rietveld refinement of the final structural model is shown in Fig. 3 ▸. The refinement included lattice parameters, pseudo-Voigt peak shape, background, zero error, axial divergence correction, axial strain broadening tensors, atomic parameters, and thermal displacement parameters of non-H atoms.
Supplementary Material
Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2414314624011799/wm4223sup1.cif
CCDC reference: 2407647
Additional supporting information: crystallographic information; 3D view; checkCIF report
Acknowledgments
We gratefully acknowledge M. A. K. Ahmed for synthesis of the sample. We also acknowledge the expertise of the staff at the Swiss–Norwegian Beam Lines at ESRF, Grenoble.
full crystallographic data
Tin(IV) sulfate dihydrate. Crystal data
| Sn(SO4)2·2H2O | Z = 2 |
| Mr = 346.86 | F(000) = 332 |
| Monoclinic, P21/c | Dx = 3.120 Mg m−3 |
| Hall symbol: -P 2ycb | Synchrotron radiation, λ = 1.00098 Å |
| a = 7.03475 (5) Å | µ = 10.46 mm−1 |
| b = 5.65165 (5) Å | T = 293 K |
| c = 9.70464 (7) Å | White |
| β = 106.8524 (4)° | cylinder, 40 × 0.5 mm |
| V = 369.27 (1) Å3 | Specimen preparation: Prepared at 368 K |
Tin(IV) sulfate dihydrate. Data collection
| High-resolution sychrotron diffractometer | Absorption correction: for a cylinder mounted on the φ axis |
| Specimen mounting: Capillary | |
| Data collection mode: transmission | 2θmin = 8.207°, 2θmax = 53°, 2θstep = 0.007° |
| Scan method: step |
Tin(IV) sulfate dihydrate. Refinement
| Rp = 0.024 | 4 restraints |
| Rwp = 0.033 | 8 constraints |
| Rexp = 0.017 | H-atom parameters constrained |
| R(F) = 0.045 | Weighting scheme based on measured s.u.'s |
| 6400 data points | (Δ/σ)max = 0.044 |
| Profile function: Pseudo-Voigt | Background function: Manual background combined with 5 Legendre polynoms |
| 46 parameters | Preferred orientation correction: none |
Tin(IV) sulfate dihydrate. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
| x | y | z | Uiso*/Ueq | ||
| Sn1 | 0.5 | 0 | 0 | 0.0331 (3)* | |
| S1 | 0.2572 (4) | 0.2445 (5) | 0.2045 (3) | 0.0339 (8)* | |
| O1 | 0.4385 (6) | 0.1591 (8) | 0.1624 (5) | 0.0244 (18)* | |
| O2 | 0.1956 (6) | 0.4801 (8) | 0.1454 (4) | 0.0324 (16)* | |
| O3 | 0.1010 (6) | 0.0638 (8) | 0.1670 (5) | 0.043 (2)* | |
| O4 | 0.3254 (7) | 0.2572 (8) | 0.3653 (4) | 0.0187 (17)* | |
| O5 | 0.7294 (8) | 0.2365 (9) | 0.0353 (6) | 0.0414 (19)* | |
| H1 | 0.76 | 0.35 | −0.03 | 0.01* | |
| H2 | 0.855 | 0.16 | 0.078 | 0.01* |
Tin(IV) sulfate dihydrate. Geometric parameters (Å, º)
| Sn1—O1 | 1.968 (6) | S1—O2 | 1.465 (6) |
| Sn1—O4i | 2.042 (5) | S1—O3 | 1.467 (6) |
| Sn1—O5 | 2.046 (6) | S1—O4 | 1.495 (5) |
| S1—O1 | 1.526 (6) | ||
| H1—O5—H2 | 103.2 (6) | O1—S1—O3 | 109.7 (3) |
| O1ii—Sn1—O4i | 88.53 (18) | O1—S1—O4 | 104.7 (3) |
| O1ii—Sn1—O4iii | 91.47 (18) | O2—S1—O3 | 114.9 (3) |
| O1ii—Sn1—O5 | 95.0 (2) | O2—S1—O4 | 109.5 (3) |
| O1ii—Sn1—O5ii | 85.0 (2) | O3—S1—O4 | 106.5 (3) |
| O1—S1—O2 | 110.9 (3) |
Symmetry codes: (i) −x+1, y−1/2, −z+1/2; (ii) −x+1, −y, −z; (iii) x, −y+1/2, z−1/2.
Tin(IV) sulfate dihydrate. Hydrogen-bond geometry (Å, º)
| D—H···A | D—H | H···A | D···A | D—H···A |
| O5—H1···O2iv | 0.969 (6) | 1.574 (5) | 2.541 (8) | 175.6 (4) |
| O5—H2···O3v | 0.963 (6) | 1.780 (4) | 2.735 (7) | 171.0 (4) |
Symmetry codes: (iv) −x+1, −y+1, −z; (v) x+1, y, z.
Funding Statement
Funding for this research was provided by: Norges Forskningsråd (grant No. 325345).
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2414314624011799/wm4223sup1.cif
CCDC reference: 2407647
Additional supporting information: crystallographic information; 3D view; checkCIF report