Crystal structures and Hirshfeld surface analyses of (N-hexyl-N-methyldithiocarbamato-κ2 S,S′)triphenyltin(IV) and [N-methyl-N-(2-phenylethyl)dithiocarbamato-κ2 S,S′]triphenyltin(IV)

The metal coordination geometry in each of the title molecules, [Sn(C6H5)3(C8H16NS2)] (I) and [Sn(C6H5)3(C10H12NOS2)] (II), is based on a heavily distorted tetrahedron owing to the asymmetric mode of coordination of the dithiocarbamate ligand. The persence of C—H⋯π(phenyl) interactions in the crystals lead to dimeric aggregates in (I) and supramolecular chains (II).


Figure 1
The molecular structures of (a) (I) and (b) (II), showing the atomlabelling schemes and displacement ellipsoids at the 50% probability level.

Supramolecular features
Tables 2 and 3 list the geometric parameters characterizing the intermolecular interactions operating in the crystals of (I) and (II), respectively. The molecular packing of (I) features centrosymmetric dimeric aggregates sustained by four phenyl-C-HÁ Á Á(phenyl) interactions whereby all of the participating groups are derived from Sn-bound phenyl rings, Fig. 2a.
Such cooperative C-HÁ Á Á(phenyl) embraces have been described for many phenyl-rich systems and in instances  Table 2 Hydrogen-bond geometry (Å , ) for (I).

Figure 2
Molecular packing in the crystal of (I): (a) supramolecular dimer sustained by a four-fold embrace of phenyl-C-HÁ Á Á(phenyl) interactions shown as purple dashed lines (for clarity, the phenyl rings are shown as small spheres, the interacting phenyl rings are highlighted in purple and only the N-bound carbon atoms of the dithiocarbamate substituents are shown) and (b) a view of the unit-cell contents shown in projection down the b axis. Table 3 Hydrogen-bond geometry (Å , ) for (II).

Figure 3
Molecular packing in the crystal of (II): (a) supramolecular chain sustained by C-HÁ Á Á(phenyl) interactions shown as purple dashed lines and (b) a view of the unit-cell contents in projection down the b axis. One chain is highlighted in space-filling mode.
where six phenyl rings of two residues associate by edge-toface interactions, i.e. a six-fold embrace, the energies of stabilization can resemble or even exceed that provided by strong conventional hydrogen bonding (Dance & Scudder, 2009). The supramolecular dimers stack parallel to the b axis with no directional interactions between successive aggregates. Globally, columns pack into layers in the ab plane. The layers inter-digitate along the c axis, again without specific interactions between proximate residues, Fig. 2b. The molecular packing of (II) again features C-HÁ Á Á interactions, as for (I), but with both methyl-H and Sn-bound-H hydrogen atoms as donors; the Sn-phenyl rings function as acceptors. As illustrated in Fig. 3a, the C-HÁ Á Á interactions sustain a supramolecular chain aligned along the b axis. The chains pack into the three-dimensional architecture without directional interactions between then, Fig. 3b. As may be seen from Fig. 3b, centrosymmetrically related Ph 3 Sn residues approach each other so as to form phenyl-embrace interactions as found in the molecular packing of (I), but none of the putative contacts are within the standard distance criteria assumed in PLATON (Spek, 2009).

Hirshfeld surface analysis
The Hirshfeld surface calculations for the triphenyltin dithiocarbamate derivatives (I) and (II) were performed in accord with recent work on related organotin dithiocarbamates (Mohamad et al., 2017). Despite the similarity in composition, the structures of (I) and (II) exhibit different intermolecular environments because of the presence of different substituents in the respective dithiocarbamate ligands, i.e. n-hexyl in the former and phenylethyl in the latter.
The faint-red spots near the phenyl-C33 and H26 atoms in Fig. 4a reflect the presence of a weak C-HÁ Á Á interaction, as summarized in Table 4. In both images of Fig. 4, the bright-red spots appearing near Sn-bound phenyl atoms C32 and H23, methyl-H2C and n-hexyl atoms C7 and H7B are indicative of the short interatomic HÁ Á ÁH and CÁ Á ÁH/HÁ Á ÁC contacts involving these atoms, as listed in Table 4. The presence of similar intermolecular interactions in the crystal of (II) cf. (I), but involving different atoms, is also characterized by bright and faint-red spots on the Hirshfeld surfaces mapped over d norm in Fig. 5. Thus, the C-HÁ Á Á interaction is seen from the presence of bright-red spots near methyl-H2B and phenyl-C11 together with the pair of faint-red spots near the methyl-H2B and phenyl-C16 atoms in Fig. 5a. The influence of other short interatomic CÁ Á ÁH/HÁ Á ÁC contacts summarized in Table 4 are viewed as diminutive and faint-red spots near the respective atoms in Fig. 5a,b. The involvement of different atoms in the intermolecular interactions in the crystals of (I) and (II) is also confirmed from the views of their Hirshfeld surfaces mapped over electrostatic potential, Fig. 6, through the appearance of blue and red regions corresponding to positive and negative Views of Hirshfeld surface for (II) mapped over d norm in the range À0.075 to +1.363 au.

Figure 6
Views of Hirshfeld surface mapped over the electrostatic potential (the red and blue regions represent negative and positive electrostatic potentials, respectively) for a molecule of: (a) (I) in the range AE0.041 au and (b) (II) in the range À0.033 to +0.049 au.

Figure 4
Views of Hirshfeld surface for (I) mapped over d norm in the range À0.133 to +1.538 au. Table 4 Summary of short interatomic contacts (Å ) in (I) and (II).
The distinct distribution of points in the overall twodimensional fingerprint plots for (I) and (II), Fig. 8a, also highlight the different molecular environments for the two molecules. The significant contributions from HÁ Á ÁH, CÁ Á ÁH/ HÁ Á ÁC and SÁ Á ÁH/HÁ Á ÁS contacts to the Hirshfeld surfaces of both (I) and (II) are evident from Table 5. The short interatomic HÁ Á ÁH contact between the methyl-H2C and n-hexyl-H7B atoms in (I) is viewed as a pair of closely spaced overlapping peaks with their tips at d e + d i $2.0 Å in the delineated plot (McKinnon et al., 2007) Fig. 8b. A pair of well separated short peaks at d e + d i $2.2 Å observed in the corresponding fingerprint plot for (II) are due to the involvement of methyl-H2A and phenyl-H7, H9 and H23 atoms in comparatively weaker short interatomic HÁ Á ÁH contacts,

Figure 7
The immediate environment around reference molecules within d normmapped Hirshfeld surfaces for (a) (I) and (b) (II), highlighting short interatomic HÁ Á ÁH and CÁ Á ÁH/HÁ Á ÁC contacts by yellow and blue dashed lines, respectively  phenyl-C32 and -H23 atoms while the points corresponding to other short interatomic contacts are merged within the plot. The presence of a pair of twin forceps-like tips at d e + d i $ 2.7 Å in the CÁ Á ÁH/HÁ Á ÁC delineated plot for (II), Fig. 8c, also indicates the involvement of methyl-H2A and -H2B, and phenyl-C7, -C8, -C11, -C16 and -C35 atoms in short interatomic contacts, Table 4. Further, it is clear from the fingerprint plots delineated into SÁ Á ÁH/HÁ Á ÁS contacts, Fig. 8d, that the pair of spikes at d e + d i $ 3.0 Å for (I) show van der Waals contacts whereas the pair of peaks at d e + d i > 3.1 Å for (II) show contacts farther than van der Waals separation. The other interatomic contacts summarized in Table 5 make a negligible contribution to their Hirshfeld surfaces.

Database survey
The dithiocarbamate ligands reported in the present study are quite rare, despite the rather large number of crystal structures of dithiocarbamate ligands available in the crystallographic literature (Groom et al., 2016). Thus, the N-hexyl-Nmethyldithiocarbamate ligand reported in (I), i.e. dtcI, has been reported in the crystal structures of Ph 2 Sn(dtcI) 2 (Ramasamy et al., 2013), In(dtcI) 3 (Park et al., 2003), and in Bi(dtcI) 3 and its 1:1 1,10-phenanthroline adduct (Monteiro et al., 2001). The uniform motivation for these studies was for their evaluation as useful precursors for the deposition of heavy element sulfide nanomaterials. In terms of the molecular structures, no special features in the mode of coordination are noted in the tin (Tiekink, 2008), indium (Heard, 2005) and bismuth (Lai & Tiekink, 2007) compounds. The Nmethyl-N-phenylethyldithiocarbamate ligand, i.e. dtcII, has been reported only in its binary mercury(II) compound, i.e. Hg(dtcII) 3 (Green et al., 2004), and again, its study was motivated by the desire to generate -HgS thin films and its structure confirms to expectation .
Reflecting the interest in organotin dithiocarbamates, including their biological activity, there are over 50 structures of general formula Ph 3 Sn(S 2 CNRR') in the Cambridge Structural Database (Groom et al., 2016). Of these, seven are binuclear and are better represented as Ph 3 SnS 2 CN-R-NCS 2 SnPh 3 . In all, there are 56 independent coordination geometries and all conform to the same structural motif as described above for (I) and (II). The average Sn-S short bond length is 2.47 Å and the average Sn-S long bond length is 3.04 Å . This gives rise to an average Á(Sn-S) of 0.57 Å . These values indicate the structures of (I) and (II) are outliers in that the values of Sn-S long are generally longer than usually observed. An analysis of the available crystallographic data showed the shortest Sn-S1 bond length occurred in the structure of Ph 3 Sn(S 2 CNEt 2 ) [(III); Hook et al. 1994 Table 6. The lack of systematic variations in these structural parameters is borne out by the disparity of the cited bonds with the second tin centre of non-symmetric (IV) and the second independent molecule of (VI). Thus, the range of Á(Sn-S) for all structures was 0.40 to 0.74, with the correlation coefficient from the plot of Sn-S short versus Sn-S long being 0.52. Such a lack of correlation has often been noted in the structural chemistry of organotin dithiocarbamates and has been ascribed to the dictates of the molecular packing (Buntine et al., 1998;Tiekink et al., 1999;Muthalib et al., 2014).

Synthesis and crystallization
All chemicals and solvents were used as purchased. The melting points were determined using an automated meltingpoint apparatus (MPA 120 EZ-Melt). C, H, N and S analyses were performed on a Leco CHNS-932 Elemental Analyzer. The IR spectra were obtained on a Perkin Elmer Spectrum GX from 4000 to 400 cm À1 . NMR spectra were recorded in CDCl 3 at room temperature on a Bruker AVANCE 400 111 HD.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 7. 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). For (I), the maximum and minimum residual electron density peaks of 1.75 and 1.51 e Å À3 , respectively, are located 0.95 and 0.86 Å from the Sn atom. For (II), the maximum and minimum residual electron density peaks of 1.47 and 1.58 e Å À3 , respectively, are located 0.96 and 0.68 Å from the C11 and Sn atoms, respectively.   (Farrugia, 2012), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010

(N-Hexyl-N-methyldithiocarbamato-κ 2 S,S′)triphenyltin(IV) (I)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.75 e Å −3 Δρ min = −1.50 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. Refinement. The maximum and minimum residual electron density peaks of 1.75 and 1.50 eÅ -3 , respectively, were located 0.95 Å and 0.86 Å from the Sn atom.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 1.47 e Å −3 Δρ min = −1.58 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. Refinement. The maximum and minimum residual electron density peaks of 1.47 and 1.58 eÅ -3 , respectively, were located 0.96 Å and 0.68 Å from the C11 and Sn atoms, respectively.