trans-Dichloridobis(dimethyl sulfoxide-κO)bis(4-fluorobenzyl-κC 1)tin(IV): crystal structure and Hirshfeld surface analysis

The octahedrally coordinated SnIV atom in [Sn(C7H6F)2Cl2(C2H6OS)2] is located on a centre of inversion so the resulting donor C2Cl2O2 donor set is all-trans. The three-dimensional molecular packing is sustained by C—H⋯F, C—H⋯Cl and C—H⋯π interactions.


Chemical context
The structural chemistry of organotin(IV) compounds with multidentate Schiff base ligands has been of interest since the observation of the diversity in their supramolecular association patterns (Teoh et al., 1997;Dey et al., 1999). Typically, these multidentate ligands bind to the tin atom through the phenolic-O, imine-N, oxime-O or even oxime-N atoms. In view of this, the coordination of these multidentate ligands to (organo)tin may lead to more thermodynamically stable organotin complexes, in contrast to those with monodentate ligands (Vallet et al., 2003;Contreras et al., 2009), a feature which could potentially be useful in catalytic studies (Yearwood et al., 2002). In consideration of this and as part of ongoing work with multidentate ligands of organotin compounds (Lee et al., 2004), an attempt to synthesize an adduct of the potentially tetradentate Schiff base N,N-1,1,2,2-dinitrilevinylenebis(5-bromosalicylaldiminato) with di(p-fluorobenzyl)tin(IV) dichloride was made.
The complex was obtained as an orange powder and was successfully characterized using various spectroscopic methods including 1 H NMR spectroscopy. Upon interaction with DMSO-d 6 , in the context of NMR studies, colourless crystals were obtained after several weeks standing. The formation of the new title compound, (I), is likely due to degradation of the complex while stored in the NMR tube. In the present contribution, the crystal and molecular structures of (I) are described as well as a detailed analysis of the intermolecular association through a Hirshfeld surface analysis.

Structural commentary
The molecular structure of (I), Fig. 1, has the Sn IV atom situated on a crystallographic centre of inversion. The Sn IV atom is coordinated by monodentate ligands, i.e. chloride, sulfoxide-O and methylene-C atoms. From symmetry, each donor is trans to a like atom resulting in an all-trans-C 2 Cl 2 O 2 donor set about the Sn IV atom. The donor set defines a distorted octahedral geometry owing, in part, to the disparate Sn-donor atom bond lengths, Table 1. The angles about the Sn IV atom differ relatively little from the ideal octahedral angles with the maximum deviation of ca 6 noted for the C1-Sn-O1 angle, Table 1.

Supramolecular features
The molecular packing in (I) comprises C-HÁ Á ÁF, C-HÁ Á ÁCl and C-HÁ Á Á interactions which combine to generate a three-dimensional network, Table 2. The chloride atom participates in phenyl-C6-HÁ Á ÁCl1 and methyl-C8-HÁ Á ÁCl1 interactions. As each chloride atom is involved in two C-HÁ Á ÁCl interactions and there are two chloride atoms per molecule, the C-HÁ Á ÁCl interactions extend laterally to give rise to a supramolecular layer in the bc plane, Fig. 2a. Layers are connected along the a axis by phenyl-C3-HÁ Á ÁF1 and methyl-C9-HÁ Á Á(phenyl) interactions to consolidate the molecular packing, Fig. 2b  The molecular packing in (I): (a) supramolecular layer in the bc plane sustained by C-HÁ Á ÁCl interactions and (b) a view of the unit-cell contents in projection down the c axis. The C-HÁ Á ÁCl, C-HÁ Á ÁF and C-HÁ Á Á interactions are shown as orange, blue and purple dashed lines, respectively.

Figure 1
The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. The Sn IV atom lies on a centre of inversion; unlabelled atoms are related by the symmetry operation 1 À x, 1 À y, 1 À z.

Hirshfeld surface analysis
The Hirshfeld surface analysis on the structure of (I) provides more insight into the molecular packing and was performed as described recently (Wardell et al., 2016). It is evident from the bright-red spots appearing near the chloride and fluoride atoms on the Hirshfeld surface mapped over d norm in Fig. 3 that these atoms play a significant role in the molecular packing. Thus, the bright-red spots near phenyl-H6, methyl-H8B and a pair near Cl1 in Fig. 3 indicate the presence of bifurcated C-HÁ Á ÁCl interactions formed by each of the chloride atoms. Similarly, the pair of red spots near phenyl-H3 and F1 atoms are associated with the donor and acceptor of C-HÁ Á ÁF interactions, respectively. The donors and acceptors of C-HÁ Á ÁCl and C-HÁ Á ÁF interactions are also represented with blue (positive potential) and red regions (negative potential), respectively, on the Hirshfeld surface mapped over the electrostatic potential in Fig. 4. In addition to above, the Cl1 and F1 atoms also participate in short interatomic contacts with methyl-H atoms, Table 3. The presence of faint-red spots near the phenyl-C4 and methyl-C9 atoms in Fig. 3 indicate their participation in a short interatomic CÁ Á ÁC contact, Table 3, which compliments the methyl-C-HÁ Á Á(phenyl) contact described above. The presence of the C-HÁ Á Á interaction is also evident from the view of Hirshfeld surface mapped over the electrostatic potential around participating atoms, Fig. 4; the donors and acceptors of these interactions are viewed as the convex surface around atoms of the methyl-C9 groups and the concave surface above the (C2-C7) phenyl ring, respectively. The immediate environments about a reference molecule within d norm -and shape-index-mapped Hirshfeld surfaces highlighting the various C-HÁ Á ÁCl, C-HÁ Á ÁF and C-HÁ Á Á interactions are illustrated in Fig. 5a-c, respectively. The overall two-dimensional fingerprint plot and those delineated into HÁ Á ÁH, ClÁ Á ÁH/HÁ Á ÁCl, FÁ Á ÁH/HÁ Á ÁF, CÁ Á ÁH/ HÁ Á ÁC and OÁ Á ÁH/HÁ Á ÁO contacts (McKinnon et al., 2007) are illustrated in Fig. 6a-f, respectively, and their relative contributions to the Hirshfeld surfaces are summarized in Table 4. It is clear from the fingerprint plot delineated into HÁ Á ÁH contacts, Fig. 6b, that although these contacts have the greatest contribution, i.e. 45.7%, to the Hirshfeld surface, the disper- A view of the Hirshfeld surface for (I) mapped over d norm over the range À0.049 to 1.356 au.

Figure 4
A view of the Hirshfeld surface for (I) mapped over the electrostatic potential in the range AE0.095 au. Table 3 Summary of short interatomic contacts (Å ) in (I).
Cg1 is the centroid of the C2-C7 ring. Symmetry codes: (ii) Àx; y þ 1 2 ; Àz þ 1 2 ; (iii) x; Ày À 1 2 ; z À 1 2 ; (iv) Àx þ 1; y À 1 2 ; Àz þ 1 2 ; (v) x þ 1; y; z.  Table 4, is due to the relative positions of the chloride and fluoride atoms in the molecule, the fluoride atoms being at the extremities and the chloride atoms near the tin(IV) atom. However, the ClÁ Á ÁH/HÁ Á ÁCl contacts have a greater influence on the molecular packing as viewed from the delineated fingerprint plot in Fig. 6c. The forceps-like distribution of points in the plot with tips at d e + d i $2.8 Å result from the bifurcated C-HÁ Á ÁCl interactions, and points at positions less than the sum of their van der Waals radii are ascribed to the short interatomic ClÁ Á ÁH/HÁ Á ÁCl contacts, the green appearance due to high density of interactions. Similarly, a pair of short spikes at d e + d i $2.5 Å in the fingerprint plot delineated into FÁ Á ÁH/HÁ Á ÁF contacts, Fig. 6d, are indicative of intermolecular C-HÁ Á ÁF interactions with the short interatomic FÁ Á ÁH/HÁ Á ÁF contacts merged within the fingerprint plot. It is important to note from the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts, Fig. 6e, that even though their interatomic distances are equal to or greater than the sum of their van der Waals radii, i.e. 2.9 Å , the 12.8% contribution from these to the Hirshfeld surfaces are indicative of the presence of C-HÁ Á Á interactions in the structure. This is also justified from the presence of short interatomic CÁ Á ÁC contacts, Fig. 5c and   contributions from the other contacts listed in Table 2 have a negligible effect on the packing.

Database survey
There are three related structures of the general formula R 2 SnX 2 (DMSO) 2 in the crystallographic literature (Groom et al., 2016). Key bond angles for these are listed in Table 5. The Me 2 SnBr 2 (DMSO) 2 compound (Aslanov et al., 1978) is analogous to (I) in that the Sn IV atom is located on a centre of inversion and hence, is an all-trans isomer. The two remaining structures have a different arrangements of donor atoms with the common feature being the trans-disposition of the Snbound organic groups, with the halides and DMSO-O atoms being mutually cis, i.e. R = Me and X = Cl (Aslanov et al., 1978;Isaacs & Kennard, 1970) and R = Ph and X = Cl (Sadiq-ur-Rehman et al., 2007). Clearly, further studies are required to ascertain the factor(s) determining the adoption of one coordination geometry over another.

Synthesis and crystallization
All chemicals and solvents were used as purchased without purification. Di(p-fluorobenzyl)tin dichloride was prepared in accordance with the literature method (Sisido et al., 1961). All reactions were carried out under ambient conditions. The melting point was determined using an Electrothermal digital melting point apparatus and was uncorrected. The IR spectrum was obtained on a Perkin Elmer Spectrum 400 FT Mid-IR/Far-IR spectrophotometer in the range 4000 to 400 cm À1 . The 1 H NMR spectrum was recorded at room temperature in CDCl 3 solution on a Jeol ECA 400 MHz FT-NMR spectrometer. N,N 0 -1,1,2,2-Dinitrilevinylenebis(5-bromosalicylaldiminato) (1.0 mmol, 0.401 g; prepared by the condensation reaction between diaminomaleonitrile and 5-bromosalicylaldehyde in a 2:1 molar ratio in ethanol) and triethylamine (1.0 mmol, 0.14 ml) in ethyl acetate (25 ml) was added to di(pfluorobenzyl)tin dichloride (1.0 mmol, 0.183 g) in ethyl acetate (10 ml). The resulting mixture was stirred and refluxed for 4 h. The filtrate was evaporated until a dark-orange precipitate was obtained. The precipitate was dissolved in DMSO-d 6 solution in a NMR tube for 1 H NMR spectroscopic characterization. After the analysis, the tube was set aside for a month and colourless crystals of (I) suitable for X-ray crystallographic studies were obtained from the slow evaporation. Yield: 0.060 g, 11%; m.p: 399 K. IR (cm À1 ):

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 6. Carbon-bound H-atoms were placed in calculated positions (C-H = 0.95-0.99 Å ) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U eq (C).    SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics:

trans-Dichloridobis(dimethyl sulfoxide-κO)bis(4-fluorobenzyl-κC 1 )tin(IV)
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.