Ba3[Sn(OH)6][SeO4]2·3H2O, a hydrated 1:2 double salt of barium hexa­hydroxidostannate(IV) and barium selenate(VI)

Reuter, H.; Kamaha, S.

doi:10.1107/S2056989022007198

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Volume 78| Part 8| August 2022| Pages 809-813

https://doi.org/10.1107/S2056989022007198

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Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O, a hydrated 1:2 double salt of barium hexahydroxidostannate(IV) and barium selenate(VI)

Hans Reuter ^a ^* and Shouassi Kamaha ^a

^aChemistry, Osnabrück University, Barabarstr. 7, 49069 Osnabrück, Germany
^*Correspondence e-mail: hreuter@uos.de

Edited by S. Parkin, University of Kentucky, USA (Received 28 June 2022; accepted 12 July 2022; online 19 July 2022)

Single crystals of tribarium hexahydroxidostannate(IV) bis[selenate(VI)] trihydrate, Ba₃H₁₂O₁₇Se₂Sn or Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O, prepared from solid BaSnO₃ and aqueous Na₂[SeO₄] solutions have hexagonal (P6₃) symmetry. The structure consists of four different primary building units: a hexahydroxidostannate(IV) ion, two different selenate(VI) ions, all three of point group symmetry C₃, and a mono-capped {BaO₉}-square antiprism of point group symmetry C₁. The secondary building units result from three of the barium coordination polyhedra linked together via common edges. While one of the two tetrahedral voids formed from these trimeric units is filled by one bidentate, chelating μ₂-selenate ion, the other one remains unoccupied as the corresponding second selenate ion only acts as a monodentate, μ₁-ligand. SBUs are completed by hexahydroxidostannate(IV) ions sharing adjacent edges on the uncapped faces of the three, mono-capped square antiprisms. These SBUs are arranged into layers via common edges on the uncapped, square faces of the {BaO₉} coordination polyhedra in a way that the hexahydroxidostannate(IV) ions act as linkage between two neighboring layers.

Keywords: crystal structure; double salt; hexahydroxidostannate(IV); selenate(VI); primary building units; secondary building units.

CCDC reference: 2189782

1. Chemical context

The hexahydroxidostannate(IV) ion, [Sn(OH)₆]²⁻, is a well established tin(IV) anion in chemistry (Scholder, 1981 ), mineralogy (Strunz & Nickel, 1998 ) and even archaeology (Basciano et al. 1998 ), although the number of well defined and structurally described compounds is rather low, especially in case of two-valent cations as these compounds are only slightly soluble. In a former paper (Kamaha & Reuter, 2009 ), we demonstrated strategies for how to circumvent these difficulties by combining slow anion formation with slow crystallization, mimicking to some extent geochemical crystal formation processes.

Here we present our results on experiments where we offered selenate(VI) anions parallel to the slow formation of hexahydroxidostannate(IV) ions, as possible co-anions during crystallization. In a typical experiment we exposed BaSnO₃ pellets to a Na₂SeO₄-solution, resulting after a long period in the formation of colorless, hexagonal prisms of Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O, a hydrated 1:2 double salt of barium hexahydroxidostannate(IV), Ba[Sn(OH)₆], and barium selenate(VI), Ba[SeO₄]. From both compounds, only the structure of the selenate has been described in the literature (Andara et al., 2005 ).

2. Structural commentary

The title compound crystallizes in the non-centrosymmetric, hexagonal space group P6₃ and was refined as an inversion twin, giving a Flack parameter of 0.037 (11). With two formula units in the unit cell, the asymmetric unit consists of 1/3 formula unit: a Ba²⁺ ion and a water molecule, both in general positions, and two crystallographically independent [SeO₄]²⁻ ions and one [Sn(OH)₆]²⁻ ion, all three having the point group C₃. In addition to the {BaO₉}-coordination polyhedron, these complex anions represent the primary building units, PBUs.

The two crystallographically different Sn–O distances within the hexahydroxidostannate(IV) anion (Fig. 1, Table 1) are identical within standard deviations [d(Sn1—O1) = 2.052 (2) Å and d(Sn1—O2) = 2.054 (2) Å]. The mean value of 2.053 (2) Å is somewhat shorter than the mean value of 2.060 (10) Å observed in other hexahydroxidostannates (Kamaha & Reuter, 2009), but lies in the observed range of 2.039–2.075 Å. Deviations from the geometry of a regular octahedron are better expressed in terms of the bond angles, best described by the non-linearity of the octahedron axes, which show bond angles of 178.7 (1)°. All oxygen atoms of the [Sn(OH)₆]²⁻ ion coordinate to two different Ba atoms in a μ₂-coordination mode, while the hydrogen atoms are involved in hydrogen bonds (Table 2) with the oxygen atoms O3 and O7 of the two different [SeO₄]²⁻ ions.

Table 1
Selected geometric parameters (Å, °)

Se1—O3	1.634 (2)	Se2—O7	1.633 (2)
Se1—O4	1.654 (4)	Se2—O6	1.648 (4)

O3ⁱ—Se1—O3	110.09 (8)	O7ⁱ—Se2—O7	111.76 (9)
O3—Se1—O4	108.84 (8)	O7—Se2—O6	107.07 (10)
Symmetry code: (i) .

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O3	0.96	1.86	2.772 (3)	158
O2—H2⋯O7ⁱⁱ	0.96	1.85	2.773 (3)	160
O8—H8A⋯O4	0.96	1.82	2.775 (3)	173
O8—H8B⋯O7ⁱⁱⁱ	0.96	1.98	2.923 (3)	169
Symmetry codes: (ii) $[-x+2, -y+1, z-{\script{1\over 2}}]$ ; (iii) .

Figure 1
Ball-and-stick model of the [Sn(OH)₆]²⁻ ion with atom numbering of the asymmetric unit and orientation of the threefold rotation axis (blue). With exception of the hydrogen atoms, which are shown as spheres of arbitrary radius, all other atoms are drawn as displacement ellipsoids at the 40% level. Bonds between oxygen and barium are indicated as shortened, two-colored sticks while hydrogen bonds are visualized as dashed lines (red).

As a result of their C₃ symmetry, the structural parameters (Table 3) of both selenate(VI) ions are restricted to those between the two crystallographically different oxygen atoms as one (denoted apical in the following) of them is situated on the threefold rotation axis (O4 in the first selenate, O6 in the second selenate) while the others (hereafter basal) (O3/O7) are in general positions. While the mean value of 1.638 (8) Å over all eight Se—O bond lengths is in excellent agreement with the mean Se—O bond lengths in other selenates [neutron data: d(Se—O) = 1.641 Å, Mg[SeO₄]·7H₂O, T = 10 K (Fortes & Gutmann, 2014 ); d(Se—O) = 1.637 Å, Mg[SeO₄] · 9H₂O, T = 100 K (Fortes et al. 2015 ); X-ray data: d(Se—O) = 1.639 Å, Na₂[SeO₄]·1.5H₂O and Na₂[SeO₄]·10H₂O, T = 100 K (Weil & Bonneau, 2014 ), d(Se—O) = 1.639 Å, Mg[SeO₄]·6H₂O, T = 293 K (Kolitsch, 2002 )] the individual Se—O distances differ significantly, reflecting the different functionality of both kind of oxygen atoms. Bonds to the apical oxygen atoms are considerably longer [1.654 (4), 1.648 (4) Å] than those to the basal ones [1.634 (2), 1.633 (2) Å]. In the first selenate ion, the apical oxygen atom acts as acceptor of three hydrogen bonds, while the corresponding oxygen atom of the second selenate ion coordinates to three barium ions. On the other hand, the three basal oxygen atoms act as acceptor of one hydrogen bond and also perform coordinative bonds, each to a different barium ion, in the first selenate ion while those of the second selenate ion accept two hydrogen bonds. Besides bond-length differences, deviations from the geometry of a regular tetrahedron result in both selenate ions having bond angles widening between the basal oxygen atoms, giving them the shape of slightly flattened trigonal pyramids rather than strict tetrahedra (Fig. 2).

Table 3
Bond lengths (Å) within the mono-capped {BaO₉} square antiprism

Ba1—O3	2.715 (2)	Ba1—O6	2.829 (1)
Ba1—O2	2.737 (2)	Ba1—O8^iv	2.880 (2)
Ba1—O1ⁱ	2.777 (2)	Ba1—O8ⁱ	2.931 (2)
Ba1—O1ⁱⁱ	2.779 (2)	Ba1—O8^v	3.106 (3)
Ba1—O2ⁱⁱⁱ	2.782 (2)
Symmetry codes: (i) y, −x + y + 1, z + $[{1\over 2}]$ ; (ii) x − y + 1, x, z + $[{1\over 2}]$ ; (iii) −x + y + 1, −x + 2, z; (iv) −x + 2, −y + 1, z + $[{1\over 2}]$ ; (v) −y + 1, x − y, z.

Figure 2
Ball-and-stick models of the two crystallographically independent [SeO₄]²⁻ ions with atom numbering of the asymmetric unit and orientation of the threefold rotation axis (blue). With exception of the hydrogen atoms, which are shown as spheres of arbitrary radius, all other atoms are drawn as displacement ellipsoids at the 40% level. Coordination bonds between oxygen and barium are drawn as shortened, two-colored sticks, hydrogen bonds between oxygen and hydrogen atoms of water molecules and hydroxyl groups are drawn as dashed lines (red).

The coordination sphere of the barium ion consists of nine oxygen atoms: two from water molecules, four from two [Sn(OH)₆]²⁻ ions, one from the first selenate ion and two, respectively, from the second selenate ion (Fig. 3). In summary, this {Ba(μ₂-OH)₄(H₂O)₂(μ₂-O_Se2)₂(μ₁-O_Se1)} coordination sphere has the shape of a mono-capped square antiprism. The uncapped face of this coordination polyhedron only is built up from the oxygen atoms of two hexahydroxidostannate ions. Its shape is almost square [maximal angle deviations from rectangular: ±0.6 (1)°, maximal deviation from planarity: ±0.0132 Å, side lengths: 2.7705 (2)–3.1720 (2) Å]. In contrast, the capped face of the square antiprism consists of oxygen atoms from two water molecules and from basal oxygen atoms of the two different selenate ions. Its shape [maximal deviation from planarity: ±0.0022 (2) Å] is much better described as an acute trapezoid with a longer/shorter base of 4.4606 (2)/3.7164 (2) Å, legs of 3.4108 (2)/3.2331 (2) Å and angles between 103.01 (1) and 78.42 (1)°. The dihedral angle between these planes is 5.64 (1)°. These deviations from a regular square antiprism are mainly caused by coordination to the selenate ions, as the apical oxygen atom of the second one constitutes the cap of the {BaO₉} coordination polyhedron, giving rise to a bidentate-chelating coordination mode of this selenate ion while the first selenate ion only acts as monodentate ligand. Ba—O bond lengths (Table 3) range from 2.715 (2) to 3.106 (3) Å, mean value 2.837 Å. Bonds between the barium ion and the oxygen atoms of the hexahydroxidostannate ions are of comparable lengths [d(Ba-O1/O2) = 2.737 (2)–2.782 (2) Å] as are those between the barium ion and the water molecules [2.880 (2)/2.931 (2) Å]. The longest bond [d(Ba—O7) = 3.106 (3) Å] is between the barium ion and the basal oxygen atom of the second selenate ion, while the shortest one [d(Ba—O3) = 2.715 (2) Å] leads to the basal atom of the first selenate ion.

Figure 3
Ball-and-stick model of the mono-capped, square-prismatic {BaO₉} coordination polyhedron. Atom colors and bond design as in Fig. 2

. Symmetry codes: (1) y, 1 − x + y, $[{1\over 2}]$ + z; (2) 2 − x, 1 − y, $[{1\over 2}]$ + z; (3) 1 − y, x − y, z; (4) 1 − x + y, 2 − x, z; (5) 1 + x − y, x, $[{1\over 2}]$ + z.

3. Supramolecular features

The interaction of the four different PBUs is visualized in Fig. 4. The most prominent part of the resulting secondary building units, SBUs, consists of three {BaO₉}-coordination polyhedra related to each other via the threefold rotation axes in Wyckoff position b. These three PBUs are linked together via common edges, each of them composed of the coordinated water molecule and the apical oxygen atom of the second selenate ion. In addition, this selenate ion shares its remaining three, basal oxygen atoms with the three surrounding barium ions, thus filling the tetrahedral void between the three {BaO₉} coordination polyhedra. On the other hand, the opposite void of the trimeric {BaO₉} unit is empty, as the first selenate ion only shares its three basal oxygen atoms with the three {BaO₉} coordination polyhedra but not the apical one. Each SBU is completed by a hexahydroxidostannate(IV) ion sharing one edge with the uncapped face of the mono-capped {BaO₉} antiprisms.

Figure 4
Polyhedral model showing the interconnection of the PBUs (selenate ions in red, {BaO₉} coordination polyhedra in green, [Sn(OH)₆]²⁻ ions in gray) and their orientation with respect to the different threefold rotation axes (blue, letter = Wyckoff position) of space group P6₃. Oxygen atoms (red) and hydrogen atoms (gray) are drawn as spheres of arbitrary radius. Hydrogen bonds are indicated as broken red sticks, visible Ba—O coordinative bonds as shortened, two-colored sticks, and visible Sn—O bonds as shortened, brass-colored sticks. In order to show the linkage of the SBUs and to visualize the trigonal–prismatic void between the hexahydroxidostannate ions, one additional {BaO₉} coordination polyhedron and one additional [Sn(OH)₆]²⁻ ion are also shown.

These secondary building units are linked together with three others, each via a common edge of the uncapped square of the {BaO₉} coordination polyhedra. In this way, each {BaO₉} coordination polyhedron shares two opposite edges of its square faces with two neighboring barium coordination polyhedra, resulting in a trigonal–prismatic void between the three interconnected SBUs. All corners of these voids consist of hydroxyl groups from [Sn(OH)₆]²⁻ ions with the tin atoms of these PBUs situated on threefold rotation axes in Wyckoff position a.

In summary, the SBUs are arranged in layers perpendicular to the c axis direction (Fig. 5). The pores within these layers are occupied by selenate ions (Se2) of adjacent layers. These selenate ions are connected with the layer via hydrogen bonds (Table 2) to the water molecules and hydroxyl groups of the [Sn(OH)₆]²⁻ ions, while the latter cross-link adjacent layers.

Figure 5
Polyhedral model showing the aufbau principle of the layers (top view above, side view below) as result of the interconnection of the SBUs. Polyhedra colors according to Fig. 1

to 3. Isolated selenate ions (Se2) in the three-sided pores belong to adjacent layers. The corresponding hydrogen bonds are omitted for clarity.

Adjacent layers are rotated through 120° against each other, resulting in a compact crystal packing without any accessible holes, channels or pores (Fig. 6). To some extent, the complex composition of the title compound expressed by the formula M^II₃[X^IV(OH)₆][Y^VIO₄]₂·3H₂O has similarities to those of the mineral thaumasite, Ca₃[Si(OH)₆][SO₄][CO₃]·12H₂O (Edge & Taylor, 1971 ; Effenberger et al., 1983 ), also crystallizing in space group P6₃. In contrast to the title compound, the coordination polyhedron of the earth metal in this mineral is reduced from nine to eight and may be described as a one-face distorted square antiprism. While the hexahydroxidosilicate adopt a similar position as the hexahydroxidostannate ion, the two other complex anions of thaumasite are only linked via hydrogen bonds to the trimeric units of {CaO₈} polyhedra as these secondary building units are not cross-linked into layers.

Figure 6
Polyhedral model showing the packing of two layers.

4. Synthesis and crystallization

Single crystals of the title compound were obtained in a long-duration experiment exposing a BaSnO₃ (Celest) pellet prepared by heating equimolar amounts of SnO₂ and BaO for 40 h at 1688 K to 10 ml of a solution of Na₂SeO₄ (Fluka) in a rolled rim glass vessel closed with a snap-on lid. Colorless, hexagonal prisms occurred after several months in the sludge of the mouldered BaSnO₃ pellet.

5. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were clearly identified in difference Fourier syntheses. Their positions were modeled with respect to a common O—H distance of 0.96 Å and a bond angle of 104.9° in case of the water molecule before they were fixed and allowed to ride on the corresponding oxygen atoms. Refinement of two common isotropic temperature factors, one for the hydrogen atoms of the hydroxyl groups and one for the hydrogen atoms of the water molecule, allowed us to check the reliability of their positions.

Table 4
Experimental details

Crystal data
Chemical formula	Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O
M_r	972.73
Crystal system, space group	Hexagonal, P6₃
Temperature (K)	100
a, c (Å)	9.2550 (6), 11.4441 (8)
V (Å³)	848.92 (13)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	12.68
Crystal size (mm)	0.21 × 0.14 × 0.12

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.314, 0.741
No. of measured, independent and observed [I > 2σ(I)] reflections	112431, 1659, 1653
R_int	0.040
(sin θ/λ)_max (Å⁻¹)	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.008, 0.018, 1.13
No. of reflections	1659
No. of parameters	74
No. of restraints	1
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.54, −0.38
Absolute structure	Refined as an inversion twin
Absolute structure parameter	0.037 (11)
Computer programs: APEX2 and SAINT (Bruker, 2009 ), SHELXS97 (Sheldrick 2008 ), SHELXL2014/7 (Sheldrick, 2015 ), DIAMOND (Brandenburg, 2006 ), Mercury (Macrae et al. (2020 ) and publCIF(Westrip, 2010 ).

Supporting information

CCDC reference: 2189782

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989022007198/pk2667sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989022007198/pk2667Isup2.hkl

checkCIF report

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: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2006), Mercury (Macrae et al. (2020); software used to prepare material for publication: publCIF(Westrip, 2010).

Tribarium hexahydroxidostannate(IV) bis[selenate(VI)] trihydrate top

Crystal data top

Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O	D_x = 3.805 Mg m⁻³
M_r = 972.73	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P6₃	Cell parameters from 9633 reflections
a = 9.2550 (6) Å	θ = 2.5–30.6°
c = 11.4441 (8) Å	µ = 12.68 mm⁻¹
V = 848.92 (13) Å³	T = 100 K
Z = 2	Needle, colourless
F(000) = 868	0.21 × 0.14 × 0.12 mm

Data collection top

Bruker APEXII CCD diffractometer	1653 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.040
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 30.0°, θ_min = 2.5°
T_min = 0.314, T_max = 0.741	h = −13→13
112431 measured reflections	k = −13→13
1659 independent reflections	l = −16→16

Refinement top

Refinement on F²	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0035P)² + 1.0003P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.008	(Δ/σ)_max = 0.001
wR(F²) = 0.018	Δρ_max = 0.54 e Å⁻³
S = 1.13	Δρ_min = −0.37 e Å⁻³
1659 reflections	Extinction correction: SHELXL-2014/7 (Sheldrick 2015, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
74 parameters	Extinction coefficient: 0.00210 (7)
1 restraint	Absolute structure: Refined as an inversion twin.
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.037 (11)
Hydrogen site location: difference Fourier map

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.

Refinement. Refined as a 2-component inversion twin.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ba1	0.85513 (2)	0.67674 (2)	0.76533 (2)	0.00444 (4)
Sn1	1.0000	1.0000	0.51521 (5)	0.00320 (5)
O1	0.9097 (3)	0.7983 (3)	0.4052 (2)	0.0057 (4)
H1	0.8736	0.6914	0.4403	0.030 (7)*
O2	1.1069 (3)	0.9077 (3)	0.6279 (2)	0.0056 (4)
H2	1.1548	0.8586	0.5787	0.030 (7)*
Se1	0.6667	0.3333	0.50722 (5)	0.00388 (9)
Se2	0.6667	0.3333	0.96470 (5)	0.00512 (9)
O6	0.6667	0.3333	0.8207 (3)	0.0072 (7)
O4	0.6667	0.3333	0.3627 (4)	0.0076 (6)
O3	0.7824 (3)	0.5248 (3)	0.55332 (19)	0.0108 (4)
O7	0.6848 (3)	0.1745 (3)	1.0066 (2)	0.0106 (4)
O8	0.9600 (3)	0.4949 (2)	0.23440 (18)	0.0095 (4)
H8A	0.8628	0.4361	0.2827	0.054 (11)*
H8B	0.9175	0.4875	0.1568	0.054 (11)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ba1	0.00500 (6)	0.00347 (6)	0.00436 (6)	0.00175 (5)	−0.00001 (8)	−0.00006 (8)
Sn1	0.00351 (7)	0.00351 (7)	0.00258 (10)	0.00175 (3)	0.000	0.000
O1	0.0070 (11)	0.0036 (11)	0.0054 (10)	0.0018 (9)	0.0002 (8)	−0.0001 (8)
O2	0.0062 (11)	0.0066 (11)	0.0057 (10)	0.0044 (10)	0.0001 (8)	0.0009 (8)
Se1	0.00407 (14)	0.00407 (14)	0.0035 (2)	0.00204 (7)	0.000	0.000
Se2	0.00486 (14)	0.00486 (14)	0.0057 (2)	0.00243 (7)	0.000	0.000
O6	0.0085 (10)	0.0085 (10)	0.0046 (17)	0.0043 (5)	0.000	0.000
O4	0.0103 (10)	0.0103 (10)	0.0023 (13)	0.0051 (5)	0.000	0.000
O3	0.0137 (11)	0.0049 (10)	0.0087 (9)	0.0008 (8)	−0.0013 (8)	−0.0022 (8)
O7	0.0133 (11)	0.0089 (10)	0.0125 (9)	0.0077 (9)	−0.0017 (9)	0.0024 (8)
O8	0.0071 (8)	0.0113 (9)	0.0096 (10)	0.0041 (7)	0.0001 (7)	0.0006 (7)

Geometric parameters (Å, º) top

Ba1—O3	2.715 (2)	O1—Ba1^ix	2.777 (2)
Ba1—O2	2.737 (2)	O1—Ba1^viii	2.779 (2)
Ba1—O1ⁱ	2.777 (2)	O1—H1	0.9600
Ba1—O1ⁱⁱ	2.779 (2)	O2—Ba1^vii	2.782 (2)
Ba1—O2ⁱⁱⁱ	2.782 (2)	O2—H2	0.9600
Ba1—O6	2.829 (1)	Se1—O3^xi	1.633 (2)
Ba1—O8^iv	2.880 (2)	Se1—O3	1.634 (2)
Ba1—O8ⁱ	2.931 (2)	Se1—O3^v	1.634 (2)
Ba1—O7^v	3.106 (3)	Se1—O4	1.654 (4)
Ba1—Se2	3.5786 (4)	Se2—O7^xi	1.633 (2)
Ba1—Sn1^vi	3.8620 (5)	Se2—O7^v	1.633 (2)
Ba1—Sn1	3.8639 (5)	Se2—O7	1.633 (2)
Sn1—O1ⁱⁱⁱ	2.052 (2)	Se2—O6	1.648 (4)
Sn1—O1	2.052 (2)	Se2—Ba1^xi	3.5786 (4)
Sn1—O1^vii	2.052 (2)	Se2—Ba1^v	3.5786 (4)
Sn1—O2	2.054 (2)	O6—Ba1^xi	2.8288 (8)
Sn1—O2^vii	2.054 (2)	O6—Ba1^v	2.8288 (8)
Sn1—O2ⁱⁱⁱ	2.054 (2)	O7—Ba1^xi	3.106 (3)
Sn1—Ba1^viii	3.8620 (5)	O8—Ba1^xii	2.880 (2)
Sn1—Ba1^ix	3.8620 (5)	O8—Ba1^ix	2.931 (2)
Sn1—Ba1^x	3.8620 (5)	O8—H8A	0.9600
Sn1—Ba1^vii	3.8639 (5)	O8—H8B	0.9600
Sn1—Ba1ⁱⁱⁱ	3.8639 (5)

O3—Ba1—O2	77.58 (7)	Ba1^viii—Sn1—Ba1^ix	71.188 (11)
O3—Ba1—O1ⁱ	142.66 (7)	O1ⁱⁱⁱ—Sn1—Ba1^x	43.99 (7)
O2—Ba1—O1ⁱ	99.65 (6)	O1—Sn1—Ba1^x	94.36 (7)
O3—Ba1—O1ⁱⁱ	144.19 (7)	O1^vii—Sn1—Ba1^x	43.93 (7)
O2—Ba1—O1ⁱⁱ	70.22 (5)	O2—Sn1—Ba1^x	137.27 (7)
O1ⁱ—Ba1—O1ⁱⁱ	60.66 (10)	O2^vii—Sn1—Ba1^x	86.69 (7)
O3—Ba1—O2ⁱⁱⁱ	77.32 (7)	O2ⁱⁱⁱ—Sn1—Ba1^x	135.94 (6)
O2—Ba1—O2ⁱⁱⁱ	60.20 (10)	Ba1^viii—Sn1—Ba1^x	71.188 (11)
O1ⁱ—Ba1—O2ⁱⁱⁱ	69.60 (5)	Ba1^ix—Sn1—Ba1^x	71.188 (11)
O1ⁱⁱ—Ba1—O2ⁱⁱⁱ	99.11 (6)	O1ⁱⁱⁱ—Sn1—Ba1	136.01 (7)
O3—Ba1—O6	76.38 (9)	O1—Sn1—Ba1	85.66 (7)
O2—Ba1—O6	144.30 (7)	O1^vii—Sn1—Ba1	136.07 (7)
O1ⁱ—Ba1—O6	115.84 (7)	O2—Sn1—Ba1	42.73 (7)
O1ⁱⁱ—Ba1—O6	123.39 (8)	O2^vii—Sn1—Ba1	93.29 (7)
O2ⁱⁱⁱ—Ba1—O6	134.70 (7)	O2ⁱⁱⁱ—Sn1—Ba1	44.06 (6)
O3—Ba1—O8^iv	70.52 (6)	Ba1^viii—Sn1—Ba1	108.832 (5)
O2—Ba1—O8^iv	81.46 (7)	Ba1^ix—Sn1—Ba1	108.833 (5)
O1ⁱ—Ba1—O8^iv	146.58 (6)	Ba1^x—Sn1—Ba1	179.974 (12)
O1ⁱⁱ—Ba1—O8^iv	89.23 (6)	O1ⁱⁱⁱ—Sn1—Ba1^vii	136.08 (7)
O2ⁱⁱⁱ—Ba1—O8^iv	134.31 (6)	O1—Sn1—Ba1^vii	136.01 (7)
O6—Ba1—O8^iv	67.08 (4)	O1^vii—Sn1—Ba1^vii	85.66 (7)
O3—Ba1—O8ⁱ	74.22 (6)	O2—Sn1—Ba1^vii	44.06 (6)
O2—Ba1—O8ⁱ	127.90 (6)	O2^vii—Sn1—Ba1^vii	42.73 (7)
O1ⁱ—Ba1—O8ⁱ	79.11 (7)	O2ⁱⁱⁱ—Sn1—Ba1^vii	93.29 (7)
O1ⁱⁱ—Ba1—O8ⁱ	139.10 (6)	Ba1^viii—Sn1—Ba1^vii	179.974 (12)
O2ⁱⁱⁱ—Ba1—O8ⁱ	71.31 (7)	Ba1^ix—Sn1—Ba1^vii	108.832 (5)
O6—Ba1—O8ⁱ	66.39 (4)	Ba1^x—Sn1—Ba1^vii	108.832 (5)
O8^iv—Ba1—O8ⁱ	126.49 (7)	Ba1—Sn1—Ba1^vii	71.147 (11)
O3—Ba1—O7^v	126.88 (6)	O1ⁱⁱⁱ—Sn1—Ba1ⁱⁱⁱ	85.66 (7)
O2—Ba1—O7^v	136.68 (7)	O1—Sn1—Ba1ⁱⁱⁱ	136.07 (7)
O1ⁱ—Ba1—O7^v	80.61 (7)	O1^vii—Sn1—Ba1ⁱⁱⁱ	136.01 (7)
O1ⁱⁱ—Ba1—O7^v	72.68 (6)	O2—Sn1—Ba1ⁱⁱⁱ	93.29 (7)
O2ⁱⁱⁱ—Ba1—O7^v	148.89 (7)	O2^vii—Sn1—Ba1ⁱⁱⁱ	44.06 (6)
O6—Ba1—O7^v	52.54 (8)	O2ⁱⁱⁱ—Sn1—Ba1ⁱⁱⁱ	42.73 (7)
O8^iv—Ba1—O7^v	76.42 (6)	Ba1^viii—Sn1—Ba1ⁱⁱⁱ	108.832 (5)
O8ⁱ—Ba1—O7^v	94.97 (6)	Ba1^ix—Sn1—Ba1ⁱⁱⁱ	179.974 (12)
O3—Ba1—Se2	103.02 (5)	Ba1^x—Sn1—Ba1ⁱⁱⁱ	108.832 (5)
O2—Ba1—Se2	155.03 (5)	Ba1—Sn1—Ba1ⁱⁱⁱ	71.147 (11)
O1ⁱ—Ba1—Se2	94.54 (5)	Ba1^vii—Sn1—Ba1ⁱⁱⁱ	71.147 (11)
O1ⁱⁱ—Ba1—Se2	99.78 (5)	Sn1—O1—Ba1^ix	105.23 (9)
O2ⁱⁱⁱ—Ba1—Se2	144.71 (5)	Sn1—O1—Ba1^viii	105.15 (10)
O6—Ba1—Se2	26.66 (7)	Ba1^ix—O1—Ba1^viii	108.03 (8)
O8^iv—Ba1—Se2	75.44 (4)	Sn1—O1—H1	117.0
O8ⁱ—Ba1—Se2	74.87 (4)	Ba1^ix—O1—H1	104.7
O7^v—Ba1—Se2	27.11 (4)	Ba1^viii—O1—H1	115.9
O3—Ba1—Sn1^vi	164.39 (5)	Sn1—O2—Ba1	106.66 (10)
O2—Ba1—Sn1^vi	89.44 (5)	Sn1—O2—Ba1^vii	105.06 (9)
O1ⁱ—Ba1—Sn1^vi	30.84 (5)	Ba1—O2—Ba1^vii	109.09 (8)
O1ⁱⁱ—Ba1—Sn1^vi	30.85 (5)	Sn1—O2—H2	105.1
O2ⁱⁱⁱ—Ba1—Sn1^vi	88.77 (5)	Ba1—O2—H2	112.5
O6—Ba1—Sn1^vi	118.99 (7)	Ba1^vii—O2—H2	117.6
O8^iv—Ba1—Sn1^vi	116.51 (4)	O3^xi—Se1—O3	110.09 (8)
O8ⁱ—Ba1—Sn1^vi	108.24 (4)	O3^xi—Se1—O3^v	110.09 (8)
O7^v—Ba1—Sn1^vi	68.67 (4)	O3—Se1—O3^v	110.09 (8)
Se2—Ba1—Sn1^vi	92.415 (12)	O3^xi—Se1—O4	108.84 (8)
O3—Ba1—Sn1	68.85 (5)	O3—Se1—O4	108.84 (8)
O2—Ba1—Sn1	30.61 (5)	O3^v—Se1—O4	108.84 (8)
O1ⁱ—Ba1—Sn1	89.73 (5)	O7^xi—Se2—O7^v	111.76 (9)
O1ⁱⁱ—Ba1—Sn1	89.69 (5)	O7^xi—Se2—O7	111.76 (9)
O2ⁱⁱⁱ—Ba1—Sn1	30.89 (5)	O7^v—Se2—O7	111.76 (9)
O6—Ba1—Sn1	144.71 (7)	O7^xi—Se2—O6	107.07 (10)
O8^iv—Ba1—Sn1	105.32 (4)	O7^v—Se2—O6	107.07 (10)
O8ⁱ—Ba1—Sn1	97.70 (4)	O7—Se2—O6	107.07 (10)
O7^v—Ba1—Sn1	162.33 (4)	O7^xi—Se2—Ba1^xi	139.72 (9)
Se2—Ba1—Sn1	170.516 (10)	O7^v—Se2—Ba1^xi	107.28 (9)
Sn1^vi—Ba1—Sn1	95.571 (6)	O7—Se2—Ba1^xi	60.11 (9)
O1ⁱⁱⁱ—Sn1—O1	86.27 (10)	O6—Se2—Ba1^xi	50.387 (8)
O1ⁱⁱⁱ—Sn1—O1^vii	86.27 (10)	O7^xi—Se2—Ba1^v	60.11 (9)
O1—Sn1—O1^vii	86.27 (10)	O7^v—Se2—Ba1^v	139.72 (9)
O1ⁱⁱⁱ—Sn1—O2	178.66 (12)	O7—Se2—Ba1^v	107.28 (9)
O1—Sn1—O2	93.93 (9)	O6—Se2—Ba1^v	50.387 (8)
O1^vii—Sn1—O2	95.06 (9)	Ba1^xi—Se2—Ba1^v	83.696 (12)
O1ⁱⁱⁱ—Sn1—O2^vii	95.07 (9)	O7^xi—Se2—Ba1	107.28 (9)
O1—Sn1—O2^vii	178.66 (12)	O7^v—Se2—Ba1	60.11 (9)
O1^vii—Sn1—O2^vii	93.93 (9)	O7—Se2—Ba1	139.72 (9)
O2—Sn1—O2^vii	84.73 (10)	O6—Se2—Ba1	50.387 (8)
O1ⁱⁱⁱ—Sn1—O2ⁱⁱⁱ	93.93 (9)	Ba1^xi—Se2—Ba1	83.697 (12)
O1—Sn1—O2ⁱⁱⁱ	95.06 (9)	Ba1^v—Se2—Ba1	83.696 (12)
O1^vii—Sn1—O2ⁱⁱⁱ	178.66 (12)	Se2—O6—Ba1^xi	102.95 (7)
O2—Sn1—O2ⁱⁱⁱ	84.73 (10)	Se2—O6—Ba1^v	102.95 (7)
O2^vii—Sn1—O2ⁱⁱⁱ	84.73 (10)	Ba1^xi—O6—Ba1^v	115.13 (5)
O1ⁱⁱⁱ—Sn1—Ba1^viii	43.93 (7)	Se2—O6—Ba1	102.95 (7)
O1—Sn1—Ba1^viii	44.00 (7)	Ba1^xi—O6—Ba1	115.13 (5)
O1^vii—Sn1—Ba1^viii	94.36 (7)	Ba1^v—O6—Ba1	115.13 (5)
O2—Sn1—Ba1^viii	135.94 (6)	Se1—O3—Ba1	135.14 (12)
O2^vii—Sn1—Ba1^viii	137.27 (7)	Se2—O7—Ba1^xi	92.78 (11)
O2ⁱⁱⁱ—Sn1—Ba1^viii	86.69 (7)	Ba1^xii—O8—Ba1^ix	110.53 (7)
O1ⁱⁱⁱ—Sn1—Ba1^ix	94.36 (7)	Ba1^xii—O8—H8A	105.3
O1—Sn1—Ba1^ix	43.93 (7)	Ba1^ix—O8—H8A	119.5
O1^vii—Sn1—Ba1^ix	43.99 (7)	Ba1^xii—O8—H8B	114.2
O2—Sn1—Ba1^ix	86.69 (7)	Ba1^ix—O8—H8B	102.6
O2^vii—Sn1—Ba1^ix	135.94 (6)	H8A—O8—H8B	105.0
O2ⁱⁱⁱ—Sn1—Ba1^ix	137.27 (7)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3	0.96	1.86	2.772 (3)	158
O2—H2···O7^xii	0.96	1.85	2.773 (3)	160
O8—H8A···O4	0.96	1.82	2.775 (3)	173
O8—H8B···O7^xiii	0.96	1.98	2.923 (3)	169

Symmetry codes: (xii) −x+2, −y+1, z−1/2; (xiii) −y+1, x−y, z−1.

Bond lengths (Å) within the mono-capped {BaO₉} square antiprism top

Ba1—O3	2.715 (2)	Ba1—O6	2.829 (1)
Ba1—O2	2.737 (2)	Ba1—O8^iv	2.880 (2)
Ba1—O1ⁱ	2.777 (2)	Ba1—O8ⁱ	2.931 (2)
Ba1—O1ⁱⁱ	2.779 (2)	Ba1—O8^v	3.106 (3)
Ba1—O2ⁱⁱⁱ	2.782 (2)

Symmetry codes: (i) y, -x + y + 1, z + 1/2; (ii) x - y + 1, x, z + 1/2; (iii) -x + y + 1, -x + 2, z; (iv) -x + 2, -y + 1, z + 1/2; (v) -y + 1, x - y, z.

Funding information

We thank the Deutsche Forschungsgemeinschaft and the Government of Lower-Saxony for funding the diffractometer and acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and Open Access Publishing Fund of Osnabrück University.

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