Synthesis, X-ray diffraction and Hirshfeld surface analysis of two new hybrid dihydrate compounds: (C6H22N4)[SnCl6]Cl2·2H2O and (C8H24N4)[SnCl6]Cl2·2H2O

Two new organic–inorganic hybrid compounds have been synthesized from the same starting materials. Their crystal structures exhibits alternating inorganic and organic stacking sheets or layers in (II), with Cl− ions and water molecules occupying the space in between.


Chemical context
The introduction of organic components into inorganic systems, to form organic-inorganic hybrid materials, has attracted considerable attention since one would expect new properties that are absent in either of their building blocks (Boopathi et al., 2017;Newman et al., 1989;Chun & Jung, 2009). Moreover, halogenostannate hybrid compounds containing protonated amine cations have received considerable attention thanks to their interesting physical and chemical properties, such as magnetic, electroluminescence, photoluminescence and conductivity, which could lead to technological innovations (Aruta et al., 2005;Chouaib et al., 2015;Papavassiliou et al., 1999;Yin & Yo, 1998). Their structures are generally characterized by isolated or connected chains or clusters of MX 6 octahedra separated by the cations.
In this category of materials, the organic moieties, balancing the negative charge on the inorganic parts, usually act as structure-directing agents and greatly affect the structure and the dimensionality of the supramolecular framework (Díaz et al., 2006;Hannon et al., 2002). Furthermore, the experimental conditions employed, such as the solvent, temperature and crystallization method, can also have an important impact on the structure of the final assembly.
The syntheses of (I) and (II) were carried out with the same starting materials but under different reaction temperatures [343 K for (I) and room temperature for (II)]. Surprinsingly, compound (II) was obtained from the reaction of cyclic 1,4bis(2-aminoethyl)piperazine molecules with SnCl 2 salt. Under very mild reaction conditions, we believe that (Bis AEP) is present as an impurity in commercial TETA based on the fact that rearrangement reactions of aliphatic chelating polyamines require high pressure and temperature (Liu et al., 2015). Similar undesired reactions have occurred with the same organic cation (Cukrowski et al., 2012;Junk & Smith, 2005;Jiang et al., 2009;Ye et al., 2002).

Structural commentary
The asymmetric unit of (I) consists of one half of a [TETA] 4+ cation, one half of an inorganic [SnCl 6 ] 2-di anion, one Cl À ion and one molecule of water (Fig. 1). The [TETA] 4+ cation is located about a center of symmetry situated at the middle of the central -CH 2 -CH 2 -bond. The hexachloridostannate(IV) dianion [SnCl 6 ] 2À , lying on a centre of inversion, exhibits a nearly perfect octahedral coordination sphere with Sn-Cl bond lengths ranging from 2.4114 (6) to 2.4469 (6) Å and Cl-Sn-Cl bond angles between 88.94 (2) and 91.06 (2) .
The asymmetric unit of compound (II) contains one half of a [Bis AEP] 4+ cation, one independent molecule of water, one Cl À ion and half of an [SnCl 6 ] 2À dianion lying on a centre of inversion (Fig. 2) The molecular structure of compound (II), with the atom-numbering scheme for the asymmetric unit. Displacement ellipsoids are drawn at the 50% probability level. Only one Cl À anion and one water molecule are shown. [Symmetry codes: (i) Àx + 1, Ày + 1, Àz; (ii) Àx + 1, Ày + 1, Àz + 1.]

Figure 1
The molecular structure of compound (I), with the atom-numbering scheme for the asymmetric unit. Displacement ellipsoids are drawn at the 50% probability level. Only one Cl À anion and one water molecule are shown. [Symmetry codes: (i) Àx + 1, Ày + 2, Àz + 1; (ii) Àx + 1, Ày + 1, Àz + 1.] a center of symmetry situated at the center of the piperazin-1,4-diium ring. The nearly perfect octahedral coordination around the Sn IV atom is characterized by Sn-Cl bond lengths varying from 2.4265 (6) to 2.4331 (6) Å and Cl-Sn-Cl bond angles ranging from 88.55 (2) to 91.45 (2) for the cis angles [180 for trans angles]. The organic part is totally protonated and the piperazinium portion adopts a chair conformation, with both ammonioethyl groups being in equatorial positions.

Supramolecular features
The crystal structure of (I) has an arrangement that can be described as alternating organic [TETA] 4+ and inorganic [SnCl 6 ] 2À sheets extending along the a-axis direction. The organic cations in adjacent chains are oriented in opposite directions, forming antiparallel sheets. The isolated chloride ions Cl À and the water molecules are located in the otherwise empty space between the sheets (Fig. 3).
The crystal packing of (I) is supported by N-HÁ Á ÁCl, N-HÁ Á ÁOW and C-HÁ Á ÁCl hydrogen-bonding interactions ( Table 1). The NH 3 + group as well as the NH 2 + group of [TETA] 4+ act as hydrogen-bond donors. The DÁ Á ÁA distances for the NH 3 + group range from 2.980 (4) to 3.255 (3) Å , while DÁ Á ÁA distances of 3.026 (2) to 3.452 (2) Å are found for the NH 2+ group. The water molecules play an important role in stabilizing the crystal packing of (I) because of their strong ability to form hydrogen bonds with both hydrogen-bond donors and acceptors. By acting as hydrogen-bond donors, they bridge isolated Cl À anions and [SnCl 6 ] 2À dianions via O1W-H1WÁ Á ÁCl4 and O1W--H2WÁ Á ÁCl2 hydrogen bonds with a HÁ Á ÁCl distances of 2.60 (5) and 2.82 (5) Å , respectively. Additionally, by playing the role of acceptors, the water molecules link the inorganic moieties with the organic cations through N1 + -H1BÁ Á ÁO1W and N1 + -H1CÁ Á ÁO1W chargeassisted hydrogen bonds with HÁ Á ÁO distances of 2.09 and 2.25 Å , respectively. Detail of the hydrogen-bonding interactions in the crystal structure of (II). Hydrogen bonds are shown as green dashed lines.

Figure 3
Projection of the crystal packing of (I) wit dashed lines representing hydrogen bonds.
In (II), the isolated chloride ions, located between the [Bis AEP] 4+ cations, are joined to their adjacent water molecules through strong OW-HÁ Á ÁCl hydrogen bonds, leading to a hydrogen-bonding pattern with a R 4 2 (8) ring motif. The resulting rings, comprising N1 + -H1BÁ Á ÁO1W and C6-H5BÁ Á ÁCl4 hydrogen bonds, promote the formation of sheets of cations aligned parallel to the (1 1 0) plane (Table 2, Fig. 4). These sheets are linked to each other by charge-assisted iminium-N4 + -H4Á Á ÁCl4 hydrogen bonds, leading to the formation of organic layers parallel to the ab plane. The inorganic layers are built up from isolated [SnCl 6 ] 2À octahedra and alternate with the organic planes along the c-axis direction. Each anion is hydrogen bonded to adjacent organic cations through atoms N1 and C2 acting as donors of N-HÁ Á ÁCl and C-HÁ Á ÁCl hydrogen bonds with NÁ Á ÁCl distances varying from 3.343 (2) to 3.431 (2) Å and the CÁ Á ÁCl distances of 3.715 (3) Å .

Figure 5
A view of the Hirshfeld surface mapped over d norm and two-dimensional fingerprint plots for compounds (I) and (II).
In compounds (I) and (II), isolated Cl atoms act as potential acceptors for hydrogen bonds; this explains why the greatest contribution to the Hirshfeld surface [65.9% for (I) and 59.8% for (II)] is from the HÁ Á ÁCl/ClÁ Á ÁH contacts. As expected in organic compounds, the HÁ Á ÁH contacts are the second important contribution, i.e. 24.8% and 30.7% for (I) and (II), respectively. It is evident that van der Waals forces exert an important influence on the stabilization of the packing in the crystal structure. Since both compounds are hydrated, the fingerprint plots also show HÁ Á ÁO/OÁ Á ÁH contacts that contribute less to the Hirshfeld surfaces, making contributions of 9.3 and 9.5%, respectively.

Database survey
A search of the Cambridge Structural Database (Version 5.38, update May 2017; Groom et al., 2016) revealed no obvious analogues of (I) and (II) in the crystallographic literature. The structures of related hydrated salts with the same cations, i.e. triethylenetetraminium bis(sulfate) monohydrate, (C 6 H 22 N 4 )-SO 4 ÁH 2 O (III), and bis(2-ammonioethyl)piperazin-1,4-ium tetraperchlorate tetrahydrate, (C 8 H 24 N 4 ) 4 ClO 4 Á4H 2 O (IV), have been reported (Fu et al., 2005;Ye et al., 2002). Compound (III) was obtained indirectly by a hydrothermal synthesis using a mixture of ferric sulfate nonahydrate and triethylenetetraamine. The ionic product (IV) was also an unexpected product from the reaction between triethylenetetramine and perchloric acid. The cationic portion of the structure adopts a chair conformation and the experimental distances are close to those for the neutral ligand.

Synthesis and crystallization
All chemicals were used without further purification. A solution of an aqueous mixture of tin chloride (SnCl 2 ) and tetraethylenetetraamine in an HCl-acidified medium with a stoichiometric ratio of 1:1 was refluxed for one h at 343 K for (I) and room temperature for (II). After two weeks of slow solvent evaporation, single crystals suitable for X-ray analysis were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Approximate positions for all H atoms were first obtained from difference-Fourier maps. H atoms were then placed idealized positions and refined using the riding-atom approximation: C-H = 0.93 Å and N-H = 0.86 Å , with U iso (H) = 1.2U eq (C,N). H atoms of the water molecule were located in a difference-Fourier map and refined with U iso (H) = 1.5U eq (O).  SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg & Berndt, 2001); software used to prepare material for publication: WinGX (Farrugia, 2012).

Triethylenetetraammonium hexachloridostannate(IV) dichloride dihydrate (I)
Crystal data Special details 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. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

1,4-Bis(2-ammonioethyl)piperazin-1,4-diium hexachloridostannate(IV) dichloride dihydrate (II)
Crystal data (C 8 (2) Special details 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. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.