Distinct coordination geometries in bis[N,N-bis(2-methoxyethyl)dithiocarbamato-κ2 S,S′]diphenyltin(IV) and bis[N-(2-methoxyethyl)-N-methyldithiocarbamato-κ2 S,S′]diphenyltin(IV): crystal structures and Hirshfeld surface analysis

Two distinct coordination geometries, each based on a C2S4 donor set, are found in the title compounds, being based on an octahedron in (C6H5)2Sn(S2CN(Me)CH2CH2OMe)2 and a skew trapezoidal bipyramid in (C6H5)2Sn[S2CN(CH2CH2OMe)2]2.


Structural commentary
The asymmetric unit of (I) comprises half a molecule as the tin atom is located on a twofold rotation axis, Fig. 1. The C 2 S 4 donor set is defined by two chelating dithiocarbamate ligands and the ipso-carbon atoms of the tin-bound phenyl substituents. The difference between the Sn-S short and Sn-S long bond lengths, i.e. Á (Sn-S), is relatively small at 0.06 Å , indicating an essentially symmetric coordination mode. This symmetry is reflected in the near equivalence of the associated C1-S bond lengths with the difference between them being 0.024 Å , Table 1. The longer Sn-S2 bond is approximately trans to the ipso-carbon atom. The overall coordination geometry is based on an octahedron with the ipso-carbon atoms occupying mutually cis positions. The methoxyethyl group is approximately perpendicular to the S 2 CN core as seen in the value of the C1-N1-C3-C4 torsion angle of 93.8 (2) . The residue itself is almost planar and adopts an extended conformation as seen in the C5-O1-C4-C3 torsion angle of 175.27 (19) .
The molecule in (II), Fig. 2, lies on a general position and has a quite distinct coordination geometry. As for (I), the tin atom is located within a C 2 S 4 donor set. However, the dithiocarbamate ligand is coordinating with significantly greater values of ÁS, i.e. 0.48 and 0.46 Å for the S1-and S3-ligands,

Figure 2
The molecular structure of (II), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.

Figure 1
The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Unlabelled atoms are related by the symmetry operation (1 À x, y, 3 2 À z).
respectively, with the Sn-S short bonds in (II) being shorter than the equivalent bonds in (I) and at the same time, the Sn-S long bonds in (II) being longer than those in (I). An interesting consequence of the different modes of coordination of the dithiocarbamate ligands in the two structures is that the Sn-C bond lengths in (II) are considerably shorter than those in (I), Table 1. As the dithiocarbamate anions are approximately co-planar and the more tightly bound S1 and S3 atoms lie to the same side of the molecule, the S 4 donor atoms define a trapezoidal plane. The tin-bound ipso-carbon atoms are disposed over the weaker Sn-S bonds so that the coordination geometry is skewed trapezoidal bipyramidal. Reflecting the significant disparity in the Sn-S bonds, there are large differences in the associated C-S bonds with the shorter of these being associated with the weakly coordinating sulfur atoms, Table 1. As for (I), the methoxyethyl groups lie almost perpendicular to the plane through the S 2 CN atoms with the greatest deviation being for the O1-containing residue, i.e. the C1-N1-C5-C6 torsion angle is À81.5 (3) . For each dithiocarbamate ligand, the residues lie to either side of the S 2 CN plane, and each is as for (I), adopting an almost planar and extended conformation with the O4-residue showing the greatest deviation, albeit marginally, as seen in the C14-O4-C13-C12 torsion angle of 176.3 (2) .

Supramolecular features
Geometric parameters characterizing the intermolecular interactions operating in the crystal structures of (I) and (II) are collected in Tables 2 and 3, respectively. Based on the distance criteria in PLATON (Spek, 2009), the only significant intermolecular contact in the molecular packing of (I) is a methylene-C-HÁ Á Á (Sn-aryl) Table 2 Hydrogen-bond geometry (Å , ) for (I).
Cg1 is the centroid of the C11-C16 phenyl ring.

Table 3
Hydrogen-bond geometry (Å , ) for (II).   In the molecular packing of (II), methylene-C-HÁ Á ÁO interactions lead to linear supramolecular chains along the b axis, Fig. 4a. These pack into the three-dimensional architecture of the crystal with no directional intermolecular interactions between them, Fig. 4b.
A more detailed analysis of the molecular packing in (I) and (II) is given below in Hirshfeld surface analysis.

Hirshfeld surface analysis
Hirshfeld surfaces for (I) and (II) were mapped over d norm , d e , shape-index, curvedness and electrostatic potential with the aid of Crystal Explorer 3.1 (Wolff et al., 2012). The electrostatic potentials were calculated using TONTO (Spackman et al., 2008;Jayatilaka et al., 2005), integrated into Crystal Explorer, and were mapped on the Hirshfeld surfaces using the STO-3G basis set at Hartree-Fock level of theory over the range AE0.12 au. The contact distances d e and d i from the Hirshfeld surface to the nearest atom inside and outside, respectively, enables 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 visual summary of intermolecular contacts in the crystal.
As evident from Fig. 5, the Hirshfeld surfaces for (I) and (II) have quite different shapes reflecting the distinctive coordination geometries, and the dark-red and dark-blue regions assigned to negative and positive potentials are localized near the respective functional groups. The absence of conventional hydrogen bonds in the crystal of (I) is consistent with the non-appearance of characteristic red spots in the calculated Hirshfeld surface mapped over d norm (not shown). By contrast, in (II), the weak C-HÁ Á ÁO interaction gives rise to red spots as evident in Fig. 6.
The overall two-dimensional fingerprint plots for (I) and (II) and those delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/ HÁ Á ÁC and SÁ Á ÁH/HÁ Á ÁS contacts are illustrated in Fig. 7; their relative contributions are summarized in Table 4. The different distribution of points in the overall fingerprint plots for (I) and (II) are due to their different molecular conformations. Also, it is noted that the points are distributed in   View of Hirshfeld surfaces mapped over the electrostatic potential (the red and blue regions represent negative and positive electrostatic potentials, respectively): (a) for (I) and (b) for (II). different (d e , d i ) ranges, i.e. 1.2 to 2.7 Å for (I) and 1.2 to 2.9 Å for (II).
As evident from the data in Table 4 and the fingerprint plots in Fig. 7b, HÁ Á ÁH contacts clearly make the most significant contributions to the Hirshfeld surfaces of both (I) and (II). In the fingerprint plot of (I) delineated into HÁ Á ÁH contacts

Figure 6
Views of Hirshfeld surfaces mapped over d norm for (II).
( Fig. 7b), all the points are situated at (d e , d i ) distances equal to or greater than their van der Waals separations i.e. 1.2 Å , reflecting zero propensity to form such intermolecular contacts. By contrast, for (II), points at (d e , d i ) distances less than 1.2 Å , with the peak at d e = d i $1.2 Å , resulting from short interatomic HÁ Á ÁH contacts, Table 5. The 7.4% contribution from OÁ Á ÁH/HÁ Á ÁO contacts to the Hirshfeld surface of (II) reflects the presence of an intermolecular C-HÁ Á ÁO interaction and a short interatomic OÁ Á ÁH/HÁ Á ÁO contact (Table 5), showing a forceps-like distribution of points with the tips at d e + d i $2.5 Å in Fig. 7c. The small contribution, i.e. 4.7%, due to analogous interactions in (I) have a low density of points that are generally masked by other contacts in the plot consistent with a low propensity to form. The pair of characteristics wings with the edges at d e + d i $2.9 Å in the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts for (I) is due to the contribution of methylene-C-HÁ Á Á(Sn-aryl) interactions, Fig. 7d. The presence of these interactions are also indicated through the pale-orange spots present on the Hirshfeld surface mapped over d e , shown within the blue circle in Fig. 8a, and bright-red spots over the front side of shape-indexed surfaces identified with arrows in Fig. 8b. The reciprocal of these C-HÁ Á Á contacts, i.e. Á Á ÁH-C contacts, are seen as blue spots near the ring in Fig. 8b. The fingerprint plot for (II) delineated into CÁ Á ÁH/ HÁ Á ÁC contacts has a distinct distribution of points with the (d e , d i ) distances greater than their van der Waals separations, confirming the absence of these interactions, Fig. 7d. The conformations of dithiocarbamate ligands in both (I) and (II) limit the sulfur atoms' ability to form significant SÁ Á ÁH intermolecular interactions; these atoms are separated at distances greater than their van der Waals radii, i.e. 3.0 Å . This observation is despite the nearly symmetrical distributions of points in the respective plots for both (I) and (II), Fig. 7e, and the significant percentage contributions to their Hirshfeld surfaces (Table 5).

Database survey
Given the various applications found for tin dithiocarbamates, it is not surprising that there exists a relatively large number of structures for this class of compound. Indeed, a search of the Cambridge Structural Database (CSD; Groom et al., 2016), reveals over 300 'hits'. Structural surveys have revealed that very different coordination geometries can arise in the solid state and, even when a common structural motif is adopted, non-systematic variations in geometric parameters are observed (Tiekink, 2008     amidal species, arising as one dithiocarbamate ligand is monodentate, Fig. 9b, are found, for example, in the structure of (t-Bu) 2 Sn(S 2 CNMe 2 ) 2 (Kim et al., 1987) and correlated with bulky tin-bound groups, and seven-coordinate species, pentagonal-bipyramidal, owing to additional coordination by a heteroatom of the tin-bound residue, Fig. 9d, as for example in the structure of [MeOC( O)CH 2 CH 2 ] 2 Sn(S 2 CNMe) 2 (Ng et al., 1989). There are 16 diphenyltin bis(dithiocarbamate) structures included in the CSD and eight of these adopt the motif shown in Fig. 9c, including both the monoclinic (Lindley & Carr, 1974) and twofold symmetric tetragonal (Hook et al., 1994) polymorphs of the archetype compound Ph 2 Sn(S 2 CNEt 2 ) 2 , and eight adopt the motif shown in Fig. 9a, including both independent molecules of Ph 2 Sn[S 2 CN(Me)Hex] 2 (Ramasamy et al., 2013); the remaining structures are single phase and have one independent molecule. Such an even split suggests a fine energy balance between the adoption of one geometry over the other.

Synthesis and crystallization
Synthesis of (I). (2-Methoxyethyl)methylamine (2 mmol) dissolved in ethanol (10 ml) was stirred in an ice-bath for 30 min. A 25% ammonia solution (1-2 ml) was added to generate a basic solution. Then, a cold ethanolic solution of carbon disulfide (2 mmol    (1 mmol) dissolved in ethanol was added into the solution and further stirred for 2 h. The precipitate that formed was filtered off and washed a few times with cold ethanol to remove impurities. Finally, the precipitate was dried in a desiccator. Recrystallization was by dissolving the compound with chloroform and ethanol (2:1 v/v) ratio. This mixture was allowed to slowly evaporate at room temperature yielding colourless crystals of (I Compound (II) was prepared and recrystallized in essentially the same manner but using bis(2-methoxyethyl)amine (10 mmol) in place of (2-methoxyethyl)methylamine. m.p.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. Carbon-bound H-atoms were placed in calculated positions (C-H = 0.93-0.97 Å ) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U eq (C).

(I) Bis[N,N-bis(2-methoxyethyl)dithiocarbamato-κ 2 S,S′]diphenyltin(IV)
Crystal data [Sn(C 6  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.47 e Å −3 Δρ min = −0.30 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[N-(2-methoxyethyl)-N-methyldithiocarbamato-κ 2 S,S′]diphenyltin(IV)
Crystal data [Sn(C 6  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.66 e Å −3 Δρ min = −0.56 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq