Crystal structure, optical property and Hirshfeld surface analysis of bis[1-(prop-2-en-1-yl)-1H-imidazol-3-ium] hexachloridostannate(IV)

The title structure consists of isolated [SnCl6]2− octahedral anions separated by layers of organic 1-(prop-2-en-1-yl)-1H-imidazol-3-ium (C6H9N2)+ cations. The crystal packing features intermolecular N—H⋯Cl and C—H⋯Cl hydrogen bonds and π–π stacking interactions.

A new 0D organic-inorganic hybrid material bis[1-(prop-2-en-1-yl)-1Himidazol-3-ium] hexachloridostannate(IV), (C 6 H 9 N 2 ) 2 [SnCl 6 ], has been prepared and characterized by single-crystal X-ray diffraction, Hirshfeld surface analysis and UV-visible spectroscopy. The structure consists of isolated [SnCl 6 ] 2À octahedral anions separated by layers of organic 1-(prop-2-en-1-yl)-1H-imidazol-3-ium cations. The 1-(prop-2-en-1-yl) fragment in the organic cation exhibits disorder over two sets of atomic sites having occupancies of 0.512 (9) and 0.488 (9). The crystal packing of the title compound is established by intermolecular N/C-HÁ Á ÁCl hydrogen bond andstacking interactions. Hirshfeld surface analysis employing three-dimensional molecular surface contours and two-dimensional fingerprint plots has been used to analyse the intermolecular interactions present in the structure. The optical properties of the crystal were studied using UV-visible absorption spectroscopy, showing one intense band at 208 nm, which is attributed to -* transitions in the cations.
Imidazole was chosen as the organic cation because the resulting complexes show interesting structural, chemical and physical properties significant for photoluminescence, magnetism, ferroelectricity, and conductivity (Tritt-Goc et al., 2019;Babar et al., 2019;Ishak et al., 2019). The Hirshfeld surface analysis was performed to completely characterize the intermolecular interactions and explain the crystalline architecture. Moreover, the UV-visible spectrum was also investigated. ISSN 2056-9890

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was performed and the associated 2D fingerprint plots (McKinnon et al., 2007) generated using Crystal Explorer 17 (Turner et al., 2017). The Hirshfeld surface was calculated using a standard (high) surface resolution with the threedimensional (3D) d norm surface plotted over a fixed colour scale mapped over the range À0.208 (red) to 1.180 (blue) a.u. The d norm mapping indicates that strong hydrogen-bonding interactions, such as N-HÁ Á ÁCl hydrogen bonding between chlorine atoms and imidazolium groups and C-HÁ Á ÁCl hydrogen bonding between chlorine atoms and the hydrogen atoms of the 1-(prop-2-en-1-yl) groups, appear to be the primary interactions in the structure, seen as a bright-red area in the Hirshfeld surface (Fig. 4).
A shape-index map of the title compound was calculated in the range À0.995 to 0.996 a.u. (Fig. 4). The convex blue regions on the shape-index symbolize hydrogen-donor groups and the concave red regions symbolize hydrogen-acceptor groups.interactions are generally indicated by adjacent red and blue triangles on the shape-index map of the Hirshfeld surface.
A curvedness map of the title compound was generated in the range À3.411 to 0.368 a.u. (Fig. 4). The large flat region of green around the rings delineated by a blue outline on the Hirshfeld surface plotted over curvedness refer to thestacking interactions.
The overall 2D fingerprint plot for all contacts are shown in Fig. 5, together with their relative contributions to the Hirshfeld surface. The 2D fingerprint plots show that the dominant intermolecular HÁ Á ÁCl (N/C-HÁ Á ÁCl) and HÁ Á ÁH interactions contribute 59.8% and 25.6%, respectively, to the overall crystal packing. The fingerprint plot of HÁ Á ÁCl contacts, which represent the largest contribution to the Hirshfeld surfaces (59.8%), shows two large spikes highly concentrated at the edges, having almost the same d e + d i = 2.7 Å (Fig. 5). The HÁ Á ÁH interactions appear as the next largest region of the fingerprint plot (25.6%), and have a distinct pattern with a minimum value of d e = d i = 1 Å (Fig. 5). Apart from these above, CÁ Á ÁCl, CÁ Á ÁH, ClÁ Á ÁCl, ClÁ Á ÁN, NÁ Á ÁH, CÁ Á ÁC, and CÁ Á ÁN interactions were observed, which are summarized in Fig. 5. View of the Hirshfeld surfaces for (C 6 H 9 N 2 ) 2 [SnCl 6 ] mapped over shapeindex, d norm and curvedness.  atoms of six imidazole rings (Kurdziel & Glowiak, 2000;Kurdziel & Glowiak, 1998) or by other ligands with the imidazole rings (Glowiak & Kurdziel, 2000;Curtis et al. 2008;Kurdziel & Glowiak, 1998;Li & Liu, 2010). However, there is no structure reported of a post-transition-metal complex with 1-allylimidazole as ligand. One bismuth complex with 1-allylimidazole (C 6 H 9 N 2 ) 4 [Bi 4 I 16 ]Á2H 2 O has been recently determined by Ferjani (2020), but is not yet available in the CSD. This and the title structure have the same monoclinic crystallographic P2 1 /n symmetry. However, one has two cations in the unit cell and the other has only one. The half anionic cluster in the asymmetric unit sits on a crystallographic inversion center.

UV-visible spectroscopy
Optical absorption (OA) of the title compound was measured at ambient temperature in water. The experimental UVvisible absorption spectrum of the title compound is shown in Fig. 6. It shows one intense absorption band at 208 nm. According to a similar compound studied previously (Maalaoui et al., 2012;Lassoued et al., 2017;Hermi et al., 2020;Mathlouthi et al., 2017), we assign this band to -* transitions within the (C 6 H 9 N 2 ) + organic cations.

Synthesis and crystallization
The title compound was prepared by dissolving 0.34 g (1 mmol) of 1-allylimidazole [1-(prop-2-en-1-yl)-1H-imidazole] and 0.3 g (2 mmol) of tin(II) chloride in 10 ml of concentrated (37%) hydrochloric acid. The mixture was stirred with heating and then kept at room temperature. Three days later, colourless single crystals suitable for structural determination were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The disordered 1-(prop-2-en-1-yl) fragment in the organic cation was refined by splitting atoms C4 and C5 over two positions (C4A, C4B) and (C5A, C5B) with occupancy factors of 0.512 (9) and 0.488 (9). Geometrical restraints (SADI) on bond lengths were applied. H atoms were located in difference-Fourier maps but introduced in calculated positions and treated as riding on their parent atoms, with C-H = 0.93 and 0.97 Å , N-H = 0.86 Å with U iso (H) = 1.2U eq (C, N).    Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Bis[1-(prop-2-en-1-yl)-1H-imidazol-3-ium] hexachloridostannate(IV)
Crystal data (C 6 (10) 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.