Strontium hexa­fluorido­stannate(IV) dihydrate

Reuter, H.

doi:10.1107/S2414314626007868

inorganic compounds

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Volume 11| Part 8| August 2026| x260786

https://doi.org/10.1107/S2414314626007868

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Strontium hexafluoridostannate(IV) dihydrate

Hans Reuter ^a ^*

^aChemistry, Osnabrück University, Barabarstr. 7, 49069 Osnabrück, Germany
^*Correspondence e-mail: [email protected]

Edited by M. Weil, Vienna University of Technology, Austria (Received 29 July 2026; accepted 30 July 2026; online 4 August 2026)

Colourless, needle-like single crystals of the title compound, Sr[SnF₆]·2H₂O, were grown from stoichiometric amounts of SrF₂ and SnF₄ in boiling water. The compound is isostructural with the corresponding hexafluoridoiridate(IV) and features a nearly undistorted octahedral [SnF₆]^2– anion with C₁ point-group symmetry, as well as an Sr²⁺ ion in a distorted, square-antiprismatic coordination environment. The resulting [SrF₅(H₂O)₃] coordination polyhedra share an edge via two water molecules to form centrosymmetric dimers. As the strength of the O—H⋯F and O—H⋯O hydrogen bonds is less pronounced, the crystal packing is dominated by μ₂-F atoms between anions and cations.

Keywords: crystal structure; hexafluoridostannate(IV); coordination polyhedra; hydrogen bonds; isotypism.

CCDC reference: 2577756

Structure description

Hexafluoridostannates(IV), [SnF₆]^2–, with monovalent and divalent metal cations have long been known (Marignac, 1859 ). They occur in both hydrated and anhydrous forms. Although they have frequently been studied crystallographically in the past (e.g. Hoppe et al., 1972 ; Lari Lavassani et al., 1974 ), complete, high-resolution single-crystal data sets based on diffractometer data are rare. Fe[SnF₆]·6H₂O belongs to this group (Denes et al., 1994 ), but as its atomic coordinates have not been published or deposited, it cannot be found in any of the crystallographic databases. The situation is somewhat better in the case of simple ammonium and phosphonium cations like (Me₃NH)⁺ (dihydrate; Taha et al., 1992 ) or (Ph₄P)⁺ (anhydrous; Cortijo et al., 2018 ). Today, the [SnF₆]^2– anion is becoming increasingly important as a building block in coordination polymers (Li et al., 2024 ; Wang et al., 2024 ; Xiong et al., 2024 ).

The title compound, strontium hexafluoridostannate(IV) dihydrate, is isostructural with the corresponding hexafluoridoiridate(IV) of strontium (Smolentsev et al., 2007 ). In the [SnF₆]^2– anion, point-group symmetry C₁, Fig. 1, the tin–fluorine distances vary between 1.9356 (14) and 1.9573 (13) Å, mean value = 1.947 (10) Å, whilst the bond angles between the trans oriented fluorine atoms are 176.38 (6), 176.81 (6), and 177.37 (6)°. In other cases, these bond angles are exactly 180°, as the anion exhibits higher symmetry, and the Sn—F bond lengths are somewhat shorter as reported in older, room-temperature single-crystal studies with somewhat lower precision: Li₂[SnF₆]·2H₂O, d(Sn—F) = 1.962–1.983 Å, mean value = 1.969 (11) Å, point-group symmetry C_2h (Marseglia & Brown, 1973 ); Na₂[SnF₆], d(Sn—F) = 6 × 1.959 Å, point-group symmetry D_2h (Benner & Hoppe, 1990 ); (Me₃NH)₂[SnF₆]·2H₂O, d(Sn—F) = 1.932 (9)–1.965 (3) Å, mean value = 1.965 (19) Å, point group symmetry C_2h (Taha et al., 1992). In the tetraphenylphosphonium salt (Ph₄P)₂[SnF₆], the anion also exhibits point-group symmetry C₁, with Sn—F bond lengths between 1.953 (1) and 1.985 (1) Å, mean value 1.963 (14) Å, and trans bond angles of 179.01 (3)–178.59 (3)° (Cortijo et al., 2018).

Figure 1
Coordination polyhedra around the metal atoms in Sr[SnF₆]·2H₂O with atom numbering. The almost octahedral [SnF₆]^2– anion (green, left) and the distorted square-antiprismatic [SrF₅(H₂O)₃] polyhedron (blue, right) are on the same scale with all non-H atoms drawn as displacement ellipsoids at the 50% probability level. Covalent bonds are drawn in bronze, coordinative bonds are drawn in grey; the black dot labelled i indicates the position of the centre of symmetry generating the dimers of the strontium coordination polyhedra. [Symmetry codes: (1) 1 − x,1 − y,1 − z; (2) $[{1\over 2}]$ + x, $[{3\over 2}]$ − y, − $[{1\over 2}]$ + z; (3) $[{3\over 2}]$ − x, $[{1\over 2}]$ + y, $[{3\over 2}]$ − z; (4) 1 − x, 2 − y, 1 − z; (5) − $[{1\over 2}]$ + x, $[{3\over 2}]$ − y, − $[{1\over 2}]$ + z.]

Of the six fluorine atoms, all but one (F3) also coordinate to the strontium atom. This metal atom is surrounded by five fluorine atoms and three water molecules, arranged in a distorted square-antiprismatic configuration (Fig. 1). The Sr—F bond lengths range from 2.4252 (14)–2.4951 (14) Å, with a mean value of 2.453 (26) Å; the strontium–oxygen bond lengths are all slightly longer, ranging from 2.6183 (17)–2.7240 (16) Å. These values can be directly compared with those of the isostructural iridium compound [ambient temperature, d(Sr—F) = 2.421 (3)–2.515 (3) Å, mean value = 2.461 (34) Å, d(Sr—O) = 2.610 (4)–2.704 (4) Å]. Three water molecules coordinate to the strontium atom, yet only two water molecules appear in the molecular formula, which is due to the fact that one water molecule (O1) bridges two strontium atoms, resulting in dimers formed by edge-sharing square antiprisms [Sr(μ₂-F)₅(μ₁-H₂O)(μ₂-H₂O)]. Together with the octahedral [SnF(μ₂-F)₅] building blocks, the compact packing shown in Fig. 2 results.

Figure 2
Polyhedral representation of the crystal packing looking down the a axis. [SnF₆]²⁻ octahedra are drawn in green and the distorted [SrF₅(H₂O)₃] square antiprisms in blue; water molecules are visualized as stick models.

Both water molecules are engaged in hydrogen-bonding interactions (Table 1). Based on the relatively long donor⋯acceptor distances (in particular for the O⋯O and one of the O⋯F contacts) and the acute bond angles at the hydrogen atoms, the hydrogen-bonding interactions are considered as medium-strong to weak.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H11⋯F3ⁱ	0.96	1.92	2.796 (2)	150
O1—H12⋯O2ⁱⁱ	0.96	2.06	2.986 (2)	161
O2—H21⋯F6ⁱⁱⁱ	0.96	2.50	3.263 (2)	137
O2—H22⋯F3^iv	0.96	1.81	2.764 (2)	173
Symmetry codes: (i) $[x-{\script{1\over 2}}, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (ii) ; (iii) ; (iv) .

Synthesis and crystallization

In a beaker, 0.30 g (1.56 mmol) of SnF₄ and 0.20 g (1.56 mmol) of SrF₂ were suspended in 100 ml of water, and the mixture was heated to boiling for 10 min. under stirring. The unreacted reactants were filtered off whilst hot; colorless needles of the title compound crystallized as the solution cooled and the solvent evaporated.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The four H atoms of the water molecules were clearly identified in difference-Fourier syntheses. Their positions were modeled with a common O—H distance of 0.96 Å and a H—O—H bond angle of 105.0° before they were fixed and allowed to ride on the corresponding oxygen atom with one common isotropic temperature factor.

Table 2
Experimental details

Crystal data
Chemical formula	Sr[SnF₆]·2H₂O
M_r	356.34
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	100
a, b, c (Å)	6.0782 (4), 9.8884 (6), 11.2968 (8)
β (°)	99.154 (3)
V (Å³)	670.33 (8)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	11.75
Crystal size (mm)	0.29 × 0.07 × 0.07

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.458, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	73429, 1947, 1842
R_int	0.056
(sin θ/λ)_max (Å⁻¹)	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.014, 0.033, 1.09
No. of reflections	1947
No. of parameters	92
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.45, −0.49
Computer programs: APEX2 and SAINT (Bruker, 2009 ), SHELXS7 (Sheldrick, 2008 ), SHELXL7 (Sheldrick, 2015 ), DIAMOND (Brandenburg, 2006 ), Mercury (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2577756

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314626007868/wm4256sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314626007868/wm4256Isup2.hkl

checkCIF report

Computing details top

Strontium hexafluoridostannate(IV) dihydrate top

Crystal data top

Sr[SnF₆]·2H₂O	F(000) = 648
M_r = 356.34	D_x = 3.531 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.0782 (4) Å	Cell parameters from 9976 reflections
b = 9.8884 (6) Å	θ = 2.8–30.0°
c = 11.2968 (8) Å	µ = 11.75 mm⁻¹
β = 99.154 (3)°	T = 100 K
V = 670.33 (8) Å³	Prism, colourless
Z = 4	0.29 × 0.07 × 0.07 mm

Data collection top

Bruker APEXII CCD diffractometer	1842 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.056
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 30.0°, θ_min = 2.8°
T_min = 0.458, T_max = 0.746	h = −8→8
73429 measured reflections	k = −13→13
1947 independent reflections	l = −15→15

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.014	H-atom parameters constrained
wR(F²) = 0.033	w = 1/[σ²(F_o²) + (0.0112P)² + 1.2564P] where P = (F_o² + 2F_c²)/3
S = 1.09	(Δ/σ)_max = 0.001
1947 reflections	Δρ_max = 0.45 e Å⁻³
92 parameters	Δρ_min = −0.49 e Å⁻³
0 restraints

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	U_iso*/U_eq
Sn1	0.59421 (2)	0.53509 (2)	0.73192 (2)	0.00724 (4)
Sr1	0.66772 (3)	0.81470 (2)	0.45187 (2)	0.00759 (5)
F1	0.5712 (2)	0.64125 (15)	0.58646 (13)	0.0163 (3)
F2	0.8141 (2)	0.66012 (14)	0.81610 (13)	0.0157 (3)
F3	0.8428 (2)	0.43410 (15)	0.68662 (13)	0.0166 (3)
F4	0.6090 (2)	0.43590 (14)	0.88292 (12)	0.0151 (3)
F5	0.3769 (2)	0.40503 (14)	0.65792 (12)	0.0146 (3)
F6	0.3519 (2)	0.64425 (14)	0.77656 (12)	0.0140 (3)
O1	0.6187 (3)	1.08124 (16)	0.40924 (14)	0.0104 (3)
H11	0.5568	1.1011	0.3275	0.041 (5)*
H12	0.7467	1.1390	0.4269	0.041 (5)*
O2	1.0554 (3)	0.69766 (18)	0.51358 (16)	0.0169 (3)
H21	1.0914	0.6397	0.5821	0.041 (5)*
H22	1.1007	0.6482	0.4484	0.041 (5)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Sn1	0.00757 (7)	0.00717 (7)	0.00704 (7)	0.00000 (5)	0.00136 (5)	0.00017 (5)
Sr1	0.00768 (9)	0.00759 (9)	0.00753 (9)	0.00034 (7)	0.00130 (7)	−0.00075 (7)
F1	0.0195 (7)	0.0151 (7)	0.0160 (7)	0.0028 (6)	0.0076 (5)	0.0062 (5)
F2	0.0121 (6)	0.0125 (7)	0.0208 (7)	−0.0016 (5)	−0.0023 (5)	−0.0026 (5)
F3	0.0134 (6)	0.0191 (7)	0.0173 (7)	0.0045 (5)	0.0030 (5)	−0.0043 (6)
F4	0.0151 (7)	0.0173 (7)	0.0121 (6)	−0.0004 (5)	−0.0005 (5)	0.0065 (5)
F5	0.0149 (7)	0.0125 (6)	0.0155 (7)	−0.0005 (5)	0.0000 (5)	−0.0034 (5)
F6	0.0150 (7)	0.0143 (7)	0.0139 (7)	0.0018 (5)	0.0063 (5)	−0.0012 (5)
O1	0.0086 (7)	0.0104 (7)	0.0120 (7)	−0.0006 (6)	0.0010 (6)	−0.0007 (6)
O2	0.0131 (8)	0.0187 (9)	0.0181 (9)	0.0054 (7)	0.0003 (6)	−0.0027 (7)

Geometric parameters (Å, º) top

Sn1—F5	1.9356 (14)	Sr1—O1	2.6874 (16)
Sn1—F1	1.9361 (14)	Sr1—O1^v	2.7240 (16)
Sn1—F3	1.9464 (14)	Sr1—Sr1^v	4.4130 (4)
Sn1—F2	1.9530 (14)	F2—Sr1^vi	2.4467 (14)
Sn1—F6	1.9558 (14)	F4—Sr1^vii	2.4405 (13)
Sn1—F4	1.9573 (13)	F5—Sr1^iv	2.4951 (14)
Sr1—F1	2.4252 (14)	F6—Sr1^viii	2.4587 (13)
Sr1—F4ⁱ	2.4405 (14)	O1—Sr1^v	2.7240 (16)
Sr1—F2ⁱⁱ	2.4467 (14)	O1—H11	0.9600
Sr1—F6ⁱⁱⁱ	2.4587 (13)	O1—H12	0.9600
Sr1—F5^iv	2.4951 (14)	O2—H21	0.9600
Sr1—O2	2.6183 (17)	O2—H22	0.9600

F5—Sn1—F1	92.38 (6)	F6ⁱⁱⁱ—Sr1—O1	75.26 (5)
F5—Sn1—F3	92.90 (6)	F5^iv—Sr1—O1	139.89 (5)
F1—Sn1—F3	90.54 (6)	O2—Sr1—O1	123.41 (5)
F5—Sn1—F2	176.38 (6)	F1—Sr1—O1^v	70.46 (5)
F1—Sn1—F2	91.23 (6)	F4ⁱ—Sr1—O1^v	72.70 (5)
F3—Sn1—F2	87.32 (6)	F2ⁱⁱ—Sr1—O1^v	75.19 (5)
F5—Sn1—F6	89.30 (6)	F6ⁱⁱⁱ—Sr1—O1^v	144.70 (5)
F1—Sn1—F6	87.93 (6)	F5^iv—Sr1—O1^v	125.90 (5)
F3—Sn1—F6	177.37 (6)	O2—Sr1—O1^v	130.10 (5)
F2—Sn1—F6	90.58 (6)	O1—Sr1—O1^v	70.73 (6)
F5—Sn1—F4	88.68 (6)	F1—Sr1—Sr1^v	105.39 (3)
F1—Sn1—F4	176.81 (6)	F4ⁱ—Sr1—Sr1^v	68.05 (3)
F3—Sn1—F4	92.41 (6)	F2ⁱⁱ—Sr1—Sr1^v	71.08 (3)
F2—Sn1—F4	87.70 (6)	F6ⁱⁱⁱ—Sr1—Sr1^v	110.41 (3)
F6—Sn1—F4	89.08 (6)	F5^iv—Sr1—Sr1^v	145.86 (3)
F1—Sr1—F4ⁱ	91.63 (5)	O2—Sr1—Sr1^v	137.13 (4)
F1—Sr1—F2ⁱⁱ	100.89 (5)	O1—Sr1—Sr1^v	35.64 (3)
F4ⁱ—Sr1—F2ⁱⁱ	139.09 (5)	O1^v—Sr1—Sr1^v	35.09 (3)
F1—Sr1—F6ⁱⁱⁱ	143.93 (5)	Sn1—F1—Sr1	157.45 (8)
F4ⁱ—Sr1—F6ⁱⁱⁱ	105.42 (5)	Sn1—F2—Sr1^vi	146.56 (7)
F2ⁱⁱ—Sr1—F6ⁱⁱⁱ	86.87 (5)	Sn1—F4—Sr1^vii	148.80 (7)
F1—Sr1—F5^iv	71.21 (5)	Sn1—F5—Sr1^iv	143.71 (7)
F4ⁱ—Sr1—F5^iv	144.19 (5)	Sn1—F6—Sr1^viii	139.19 (7)
F2ⁱⁱ—Sr1—F5^iv	76.22 (5)	Sr1—O1—Sr1^v	109.28 (6)
F6ⁱⁱⁱ—Sr1—F5^iv	76.75 (5)	Sr1—O1—H11	112.9
F1—Sr1—O2	79.50 (5)	Sr1^v—O1—H11	106.7
F4ⁱ—Sr1—O2	69.27 (5)	Sr1—O1—H12	118.9
F2ⁱⁱ—Sr1—O2	151.12 (5)	Sr1^v—O1—H12	103.1
F6ⁱⁱⁱ—Sr1—O2	77.39 (5)	H11—O1—H12	105.0
F5^iv—Sr1—O2	76.67 (5)	Sr1—O2—H21	124.0
F1—Sr1—O1	140.80 (5)	Sr1—O2—H22	112.1
F4ⁱ—Sr1—O1	71.80 (5)	H21—O2—H22	105.0
F2ⁱⁱ—Sr1—O1	74.13 (5)

Symmetry codes: (i) −x+3/2, y+1/2, −z+3/2; (ii) x−1/2, −y+3/2, z−1/2; (iii) x+1/2, −y+3/2, z−1/2; (iv) −x+1, −y+1, −z+1; (v) −x+1, −y+2, −z+1; (vi) x+1/2, −y+3/2, z+1/2; (vii) −x+3/2, y−1/2, −z+3/2; (viii) x−1/2, −y+3/2, z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H11···F3ⁱⁱ	0.96	1.92	2.796 (2)	150
O1—H12···O2^ix	0.96	2.06	2.986 (2)	161
O2—H21···F6^x	0.96	2.50	3.263 (2)	137
O2—H22···F3^xi	0.96	1.81	2.764 (2)	173

Symmetry codes: (ii) x−1/2, −y+3/2, z−1/2; (ix) −x+2, −y+2, −z+1; (x) x+1, y, z; (xi) −x+2, −y+1, −z+1.

Acknowledgements

The author thanks the Deutsche Forschungsgemeinschaft and the Government of Lower-Saxony for funding the diffractometer and acknowledges support by Deutsche Forschungsgemeinschaft (DFG) and Open Access Publishing Fund of Osnabrück University.

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