[N-Benzyl-N-(2-phenylethyl)dithiocarbamato-κ2 S,S′]triphenyltin(IV) and [bis(2-methoxyethyl)dithiocarbamato-κ2 S,S′]triphenyltin(IV): crystal structures and Hirshfeld surface analysis

Heavily distorted trigonal–pyramidal coordination geometries, each based on a C3S2 donor set and with the loosely bound S atom approximately trans to one of the ipso-C atoms, are found in the title compounds (C6H5)3Sn[S2CN(Ben)CH2CH2Ph] and (C6H5)3Sn[S2CN(CH2CH2OMe)2].


Chemical context
Among the varied motivations for investigating organotin dithiocarbamate compounds, i.e. R n Sn(S 2 CNRR 0 ) 4-n where R, R 0 = alkyl, aryl, most relate to their biological activities and their usefulness as molecular, single-source precursors for the formation of tin sulfide nanoparticles (Tiekink, 2008). In terms of the latter, while triorganotin dithiocarbamates, i.e. with n = 3, have been examined in this context (Kana et al., 2001), diand mono-organotin derivatives often provide more effective precursors (Ramasamy et al., 2013). By contrast, significant interest in the biological effects of triorganotin dithiocarbamates continues. Hence, a wide variety of biological applications of triorganotin dithiocarbamates, i.e. directly related to the title compounds, have been investigated. Thus, anti-bacterial (Muthalib et al., 2015), larvicidal (Song et al., 2004), including against mosquito larvae (Basu Baul et al., 2005), insecticidal (Awang et al., 2012;Safari et al., 2013) and anti-leishmanial activities  have been investigated. However, most activity has been directed towards evaluating their potential as anti-cancer agents (Tiekink, 2008;Khan et al., 2014Khan et al., , 2015. It was in this context and during ongoing structural studies of organotin dithiocarbamates ISSN 2056-9890 (Muthalib et al., 2014;Mohamad et al., 2016) that the title compounds were synthesized. Herein, the crystal and molecular structures of (C 6 H 5 ) 3 Sn[S 2 CN(Ben)CH 2 CH 2 Ph] (I) and (C 6 H 5 ) 3 Sn[S 2 CN(CH 2 CH 2 OMe) 2 ] (II) are reported along with a detailed analysis of the supramolecular association operating in their crystal structures by means of Hirshfeld surface analysis.

Structural commentary
The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are collected in Table 1. The tin atom is bound to three phenyl groups and to the dithiocarbamate ligand. The latter coordinates asymmetrically with Á(Sn-S), being the difference between the Sn-S long and Sn-S short bond lengths, of 0.42 Å . This asymmetry is reflected in the relatively large disparity in the associated C-S bond lengths with the bond involving the tightly bound S1 atom being significantly longer than the bond involving the S2 atom, Table 1. Such a great difference might imply a monodentate mode of coordination for the dithiocarbamate ligand and the adoption of a tetrahedral coordination geometry. However, the range of tetrahedral angles if this were the case is over 30 , i.e. from a narrow 92.98 (4) for S1-Sn-C17 to a wide 124.31 (4) for S1-Sn-C29. The wide angle is due to the close approach to the tin atom of S2. Further, the Sn-C17 bond length is systematically longer than the other Sn-C bond lengths, an observation ascribed to the C17 atom being approximately trans to the incoming S2 atom, Table 1. Thus, the coordination geometry is best described as being based on a C 3 S 2 donor set. The geometry is not ideal with the value of of 0.57, cf. values of 0.0 and 1.0 for ideal square-pyramidal and trigonal-bipyramidal geometries, respectively (Addison et al., 1984), suggesting a small distortion towards trigonalbipyramidal. Distortions from the ideal can be related to the disparate Sn-donor atom bond lengths and the acute chelate angle, Table 1.
The molecular structure of (II) (Fig. 2) bears many similarities with that just described for ( The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. Table 1 Geometric data (Å , ) for (I) and (II). 158.55 (4) -S2-  0.64 Å is even greater than that of (I), indicating a more asymmetric mode of coordination of the dithiocarbamate ligand. This difference is also reflected in the associated C-S bond lengths, following the same trend as for (I) but, with Á(C-S) of 0.08 Å cf. 0.06 Å for (I). This being stated, the Sn-C14 bond length of 2.1608 (14) , with the C14 atom being trans to the S2 atom, is the longest of all six Sn-C bonds in (I) and (II). The range of tetrahedral angles, i.e. 90.94 (4) for S1-Sn-C14 to 119.54 (5) for C8-Sn-C20, is slightly narrower at less than 30 . The value of computes to 0.58, i.e. virtually identical to that in (I).

Supramolecular features
Despite there being five aromatic rings in the molecule of (I), the closest face-to-face contact between rings is > 4.0 Å . The only points of contact between molecules in the molecular packing identified by PLATON (Spek, 2009) are those of the type C-HÁ Á Á. Each of the rings of the dithiocarbamate ligand donates a hydrogen atom to a different tin-bound phenyl ring with the result that a supramolecular chain is formed along the c-axis direction, Table 2 and Fig. 3a. The chains pack without directional interactions between them, Fig. 3b. Even though there are oxygen atoms in the molecule of (II), the supramolecular association is dominated by C-HÁ Á Á contacts involving methyl-C-H and Sn-bound-phenyl-C-H as donors and only two of the Sn-bound phenyl rings as acceptors, as the (C14-C19) ring accepts two interactions, Table 3. The result of this association is the formation of supramolecular layers in the ac plane, Fig. 4a Table 2 Hydrogen-bond geometry (Å , ) for (I).

Figure 3
The molecular packing in (I): (a) supramolecular chain along the c axis sustained by dithiocarbamate-phenyl-C-HÁ Á Á(Sn-phenyl) interactions shown as purple dashed lines and (b) a view of the unit-cell contents in projection down the c axis. In (a), the accepting rings are highlighted in purple and in (b), one chain is highlighted in space-filling mode. Table 3 Hydrogen-bond geometry (Å , ) for (II).

Figure 4
The molecular packing in (II): (a) supramolecular layer parallel to the ac plane sustained by methyl-and Sn-phenyl-C-HÁ Á Á (Sn-phenyl) interactions shown as purple dashed lines and (b) a view of the unit-cell contents in projection down the a axis. In (a), the accepting rings are highlighted in purple and in (b), one layer is highlighted in space-filling mode.

Hirshfeld surface analysis
Crystal Explorer (Wolff et al., 2012) was used to generate Hirshfeld surfaces mapped over d norm , shape-index and electrostatic potential. The electrostatic potentials were calculated using TONTO (Spackman et al., 2008;Jayatilaka et al., 2005) integrated into Crystal Explorer, wherein the respective experimental structure was used as the input to TONTO. Further, the electrostatic potentials were mapped on Hirshfeld surfaces using the STO-3G basis set at the Hartree-Fock level of theory over ranges AE 0.037 au. and AE 0.048 au. for (I) and (II), respectively. The contact distances d i and d e from the Hirshfeld surface to the nearest atom inside and outside, respectively, enable the analysis of the intermolecular interactions through the mapping of d norm . The combination of d e and d i in the form of two-dimensional fingerprint plots (McKinnon et al., 2007) provides a useful summary of intermolecular contacts in the respective crystal. The different shapes of Hirshfeld surfaces for molecules (I) and (II) arise from the asymmetric geometries resulting from the different dithiocarbamate-bound functional groups, i.e. phenyl and methoxy groups in (I) and (II), respectively, Fig. 5. The images of the Hirshfeld surface mapped over electrostatic potential for (I) and (II) display dark-red and dark-blue regions, assigned to negative and positive potentials, respectively, and are localized near their respective functional   Views of Hirshfeld surfaces mapped over electrostatic potential corresponding to CÁ Á ÁH contacts (the red spots located near the phenyl rings indicate their contribution as -bond donors in the C-HÁ Á Á interactions) for: (a) (I) and (b) (II).
groups. The absence of conventional hydrogen bonds in the crystals of (I) and (II) is consistent with the non-appearance of characteristic red-spots in the Hirshfeld surface mapped over d norm (not shown). The curvature of the Hirshfeld surfaces around the phenyl rings participating as acceptors in the C-HÁ Á Á contacts determine the strength of these interactions in the crystal packing. In the structure of (I), the surfaces around the Sn-bound phenyl (C17-C22) and (C23-C28) rings are more concave than the equivalent rings participating in C-HÁ Á Á interactions in (II), indicating their greater influence upon packing, as seen in the shorter HÁ Á Áring centroid separations, Tables 2 and 3. This observation is also apparent from the Hirshfeld surfaces mapped over electrostatic potential corresponding to CÁ Á ÁH contacts for (I) and (II), both showing red spots in the images of Fig. 6 correlating with their functioning as -bond acceptors. The concave appearance of the Hirshfeld surface mapped over electrostatic potential around the Sn-bound phenyl ring (C14-C19) in the structure of (II) is indicative of its participation in two C-HÁ Á Á interactions, i.e. with the H13 and H23 hydrogen atoms. The other C-HÁ Á Á contact involves methyl-H7C atom as the donor and phenyl (C8-C13) ring as the acceptor. The shapeindexed Hirshfeld surfaces highlighting the C-HÁ Á Á contacts are shown in Fig. 7.
The overall two-dimensional fingerprint plots for (I) and (II) and those delineated into HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC and SÁ Á ÁH/HÁ Á ÁS contacts (McKinnon et al., 2007) are illustrated in Fig. 8a-d, respectively; their relative contributions are summarized in Table 4. Although the distribution of points in the overall plots of (I) and (II) have almost same (d e , d i ) ranges, i.e. between 1.2 and 2.6 Å , the densities and the areas of their distributions are different. It is evident from the data in Table 4 and the fingerprint plot delineated into HÁ Á ÁH contacts in Fig. 8b that these contacts make the most significant contribution to the Hirshfeld surfaces of both (I) and (II). In the fingerprint plot of (I) delineated into HÁ Á ÁH contacts ( Fig. 8b), all the points are situated at the (d e , d i ) distances greater than or equal to their van der Waals separations i.e. 2 x 1.2 Å , hence there is no propensity to form such intermolecular contacts. The peak at (d e , d i ) distances slightly less than van der Waals separations in the fingerprint plot for (II) is due to a short interatomic HÁ Á ÁH contact between symmetry-related methoxy-and dithiocarbamate hydrogen atoms [H7AÁ Á ÁH5A i = 2.36 Å ; symmetry code: (i) Àx, 2 À y, 1 À z]. In the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts for (I), Fig. 8c, the 32.9% contribution to the Hirshfeld surface and the symmetrical distribution of points showing bending of the pattern at (d e + d i ) min $2.8 Å is the result of short interatomic CÁ Á ÁH/HÁ Á ÁC contacts [C1Á Á ÁH32 ii = 2.85 and C14Á Á ÁH27 iii = 2.84 Å ; symmetry codes: (ii) 1 + x, y, z; (iii) 1 À x, 2 À y, Àz]. In the structure of (II), a comparatively reduced contribution from these contacts to the surface is made, i.e. 24.4%, an observation ascribed to the presence of only C-HÁ Á Á contacts in the molecular packing, with no other short inter-atomic contacts. The negligible contribution from CÁ Á ÁC contacts to the Hirshfeld surfaces indicate that despite the presence of three Sn-bound phenyl rings in the structures of both (I) and (II), and the presence of other two phenyl rings bound to the dithiocarbamate ligand in (I), the structures show no significantstacking. In the structure of (II), the presence of oxygen atoms does not have any significant influence on its molecular packing although there is 4.7% contribution from OÁ Á ÁH/HÁ Á ÁO contacts to the Hirshfeld surface. The fingerprint plots delineated into SÁ Á ÁH/HÁ Á ÁS Views of Hirshfeld surfaces mapped over shape-index (a) for (I) and (b) for (II). The different C-HÁ Á Á contacts are labelled and indicated as dashed lines. Table 4 Percentage contribution to interatomic contacts from the Hirshfeld surface for (I) and (II).
contacts for both the molecules (I) and (II), Fig. 8d, show that crowded geometries around the tin atoms prevent the sulfur atoms from forming such intermolecular contacts although these contacts have significant contributions to their respective Hirshfeld surfaces, Table 4, as well as nearly symmetrical distributions of points in their plots. This observation was also noted in an earlier study describing related organotin dithiocarbamate structures (Mohamad et al., 2016).

Database survey
According to a search of the Cambridge Structural Database (CSD; Groom et al., 2016), the dithiocarbamate ligands featuring in the present study have comparatively rare R/R 0 substituents. For example, the À S 2 CN(Ben)CH 2 CH 2 Ph anion in (I) has only one precedent, namely in Pb[S 2 CN(Ben)CH 2 CH 2 Ph] 2 (Sathiyaraj et al., 2012). There are eight examples of the À S 2 CN(CH 2 CH 2 OMe) 2 anion, as in (II), being the focus of two recent systematic studies (Hogarth et al., 2009;Naeem et al., 2010).
Reflecting the interest in organotin dithiocarbamates, there are approximately 40 examples of triphenyltin dithiocarbamate structures in the CSD, all of which present the same basic structural motif as described herein for (I) and (II). The prototype compound, Ph 3 Sn(S 2 CNEt 2 ) features the shortest Sn-S bond length of the series at 2.429 (3) Å (Hook et al., 1994). The most asymmetric mode of coordination of a dithiocarbamate ligand, i.e. with Á(Sn-S) of 0.74 Å , is found in the structure of Ph 3 Sn(4-nitrophenylpiperazine-1-dithiocarbamate) (Rehman et al., 2009). On the other hand, the most symmetric mode of coordination is found in the structure of Ph 3 Sn(4-methoxyphenylpiperazine-1-dithiocarbamate), having Á(Sn-S) of 0.42 Å (Zia-ur- Rehman et al., 2011), i.e. the same value as found in the structure of (I) reported herein.
Compound (II) was prepared in essentially the same manner as for (I) but using bis(2-methoxyethyl)amine (5 mmol) in place of N-benzyl-2-phenylethylamine.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. 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). In the refinement of (II), disorder was noted in the C5-chain of the dithiocarbamate ligand. Specifically, the C6 and O2 atoms were modelled over two positions in the ratio 0.569 (2):0.431 (2). The anisotropic displacement parameters for both components of the C6 and O5 atoms were constrained to be equivalent; further, those for the C6 atoms were restrained to be approximately isotropic. The 1,2 and 1,3 bond lengths of the disordered residual were restrained to be similar to those of the ordered arm of the dithiocarbamate ligand.

(I) [N-Benzyl-N-(2-phenylethyl)dithiocarbamato-κ 2 S,S′]triphenyltin(IV)
Crystal data [Sn(C 6  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.53 e Å −3 Δρ min = −0.61 e Å −3 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.

(II) [Bis(2-methoxyethyl)dithiocarbamato-κ 2 S,S′]triphenyltin(IV)
Crystal data [Sn(C 6  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.55 e Å −3 Δρ min = −0.61 e Å −3 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.