Crystal structures and Hirshfeld surface analyses of bis[N,N-bis(2-methoxyethyl)dithiocarbamato-κ2 S,S′]di-n-butyltin(IV) and [N-(2-methoxyethyl)-N-methyldithiocarbamato-κ2 S,S′]triphenyltin(IV)

The coordination geometry in (n-Bu)2Sn[S2CN(CH2CH2OCH3)2]2, (I), is based on a skewed trapezoidal bipyramid, while that in (C6H5)3Sn[S2CN(CH3)CH2CH2OCH3], (II), is based on a tetrahedron. In the crystal of (I), supramolecular layers parallel to (10-1) are sustained by methylene-C—H⋯O(methoxy) interactions, while in (II), centrosymmetric dimers are formed via pairwise weak phenyl-C—H⋯π(phenyl) contacts.


Chemical context
While formerly the purview of all-alkyl substituents (Hogarth, 2005;Heard, 2005), recent work in the chemistry of dithiocarbamate ligands, À S 2 CN(R)R 0 , has increasingly seen the inclusion of oxygen atoms in these N-bound groups (Hogarth et al., 2009), leading to different chemistry/biochemistry. Oxygen can be present as a hydroxyl group, giving rise to supramolecular aggregation patterns based on hydrogen bonding for otherwise non-aggregating species (Tan et al., 2016;Jotani et al., 2017) or as an ether, giving rise to compounds with biological activity (Ferreira et al., 2012). Organotin dithiocarbamates have long been known to possess biological activity, in particular as anti-tumour and antibacterial agents (Tiekink, 2008). In keeping with the aforementioned, several recent studies have appeared investigating the biological activity of metal dithiocarbamates where the ligand contains at least one 2-methoxyethyl substituent (Khan et al., 2013(Khan et al., , 2016, including anti-bacterial potential of organotins (Mohamad, Awang, Kamaludin & Abu Bakar, 2016;. The latter ISSN 2056-9890 studies have been augmented by several structural investigations in recent times Mohamad, Awang, Kamaludin, Jotani et al., 2016;Mohamad et al., 2017). In a continuation of these structural studies, herein, the crystal and molecular structures of (n-Bu) 2 Sn[S 2 CN(CH 2 CH 2 OCH 3 ) 2 ] 2 (I) and (C 6 H 5 ) 3 Sn-[S 2 CN(CH 3 )CH 2 CH 2 OCH 3 ] (II) are reported along with a Hirshfeld surface analysis to provide more details on the molecular packing, which generally lacks directional intermolecular interactions.

Structural commentary
The tin atom in (I), Fig. 1a, lies on a crystallographic twofold axis so that the asymmetric unit comprises half a molecule. The dithiocarbamate ligand coordinates to the tin atom with quite disparate Sn-S bond lengths with Á(Sn-S) = d(Sn-S long ) À (Sn-S) short = 0.38 Å , Table 1. The disparity in the Sn-S bond lengths is reflected in systematic differences in the C-S bonds lengths with the bond associated with the stronger Sn-S1 bond being significantly longer, i.e. by about 0.03 Å , than the C-S bond associated with the weaker Sn-S2 bond. The coordination environment is completed by two -carbon atoms of the n-butyl substituents. The resultant C 2 S 4 donor set defines a skew-trapezoidal bipyramidal geometry with the tinbound organic substituents lying over the weaker Sn-S2 bonds, which subtend an angle at the tin atom approximately 50 wider than that subtended by the S1 atoms, Table 1. The 2-methoxyethyl groups lie to either side of the S 2 CN residue and have very similar conformations, as seen in the values of the C1-N1-C2-C3, N1-C2-C3-O1 and C2-C3-O1-C4 torsion angles of À94.1 (4), À67.4 (4) and À177.1 (3) , indicating that À anti-clinal, À syn-clinal and À anti-periplanar descriptors, respectively, are in effect. For the O2-methoxyethyl group, the equivalent torsion angles are À82.0 (4), À70.3 (4) and À169.1 (3) . The independent n-butyl substituent has an all-trans (+ anti-periplanar) conformation, as seen in the values of the Sn-C8-C9-C10 and C8-C9-C10-C11 torsion angles of 172.9 (2) and 176.3 (3) , respectively.
The molecule in (II), Fig. 1b, lies on a general position and has a quite distinct coordination geometry owing to the presence of three tin-bound phenyl groups. As for (I), the dithiocarbamate ligand coordinates in an asymmetric mode with Á(Sn-S) being 0.55 Å . Consistent with the greater Figure 1 The molecular structures of (a) (I) and (b) (II), showing the atomlabelling schemes and displacement ellipsoids at the 50% probability level. Unlabelled atoms in (a) are related by the symmetry operation x, y, 1 2 À z. Table 1 Selected geometric parameters (Å , ) for (I).  2.5503 (9) S1-C1   (7) C11-Sn-C21 104.11 (10) S1-  119.09 (7) C11-Sn-C31 105.78 (10) S2-  155.54 (8) C21-  disparity in Sn-S bond lengths, the difference in the associated C-S bond lengths in (II) is greater cf. (I), i.e. nearly 0.07 Å , Table 2. The increased asymmetry in the mode of coordination of the dithiocarbamate ligand in (II), cf. (I), is correlated with the reduced Lewis acidity of the tin atom in the triorganotin compound, (II), compared with that in the diorganotin compound, (I). The angles subtended at the tin atom vary from a narrow 64.37 (2) for the S1-Sn-S2 chelate angle to 155.54 (8) for S2-Sn-C11. The C 3 S 2 donor set approximates a trigonal-bipyramidal geometry with the value of , an indicator of a five-coordinate coordination geometry, being 0.61, cf. 1.0 for an ideal trigonal bipyramid and 0.0 for an ideal square pyramid (Addison et al., 1984). If the coordination geometry is considered as being based on a C 3 S donor set, the range of tetrahedral angles is 91.17 (8) , for S1-Sn-C11, to 119.09 (7) , for S1-Sn-C31. The C21-Sn-C31 angle, at 115.55 (10) , is wider by 10 than the other C-Sn-C angles, a result correlated with the close approach of the S2 atom.

Supramolecular features
Geometric parameters characterizing the intermolecular interactions operating in the crystal structures of (I) and (II) are collected in Tables 3 and 4 Table 3 Hydrogen-bond geometry (Å , ) for (I).
Cg1 is the centroid of the C21-C26 ring.

Hirshfeld surface analysis
The Hirshfeld surface calculations for the organotin derivatives (I) and (II) were performed in accord with recent work on related organotin dithiocarbamate compounds (Mohamad et al., 2017), and these exhibit different intermolecular environments as described below. The bright-red spots near each of the methoxy-O1 and -O2, and methylene-H4A and H6B atoms lying on both the sides of twofold symmetry axis on the Hirshfeld surfaces mapped over d norm for (I) in Fig. 4a and b represent the dominant intermolecular C-HÁ Á ÁO contacts, Table 3. In addition, the brightred spots appearing near the methoxy-H8B and butyl-H8A atoms in Fig. 4c indicate the significant influence of intra-layer HÁ Á ÁH contacts, Table 5. On the Hirshfeld surface mapped over the electrostatic potential for (I) shown in Fig. 5a and b, the donors and acceptors are represented with blue and red regions around the respective atoms corresponding to positive and negative potentials, respectively.
The Hirshfeld surfaces mapped over d norm for (II) (not shown), indicate the absence of significant directional interactions operating in the crystal as no characteristic red spots appear on the surface. The blue and red regions on the Hirshfeld surface mapped over electrostatic potential for (II) in Fig. 5c are due to polarization of charges near the respective functional groups and do not represent any significant interaction in the crystal. The weak intermolecular C-HÁ Á Á contact and intra-layer interatomic HÁ Á ÁH contacts (Table 5) present in the crystal of (II) are illustrated in Fig. 6.
The overall two-dimensional fingerprint plots for (I) and (II), Fig. 7a and b, reveal the distinct supramolecular associations in their crystals. The terminal methoxy-ethyl and coordinated n-butyl substituents in (I) form significant intralayer HÁ Á ÁH contacts in comparison to (II), Table 5. This fact is also indicated in the fingerprint plots delineated into HÁ Á ÁH contacts (McKinnon et al., 2007), showing a short thick spike at d e + d i $ 2.0 Å and the distribution of points with greater density in (d e , d i ) range $1.0 to 1.2 Å for (I) in Fig. 7a, and a small peak at d e + d i $ 2.2 Å with relatively few points at d e + d i < 2.4 Å for (II) in Fig. 7b. The fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts for (I), Fig. 7a, characterizes intermolecular C-HÁ Á ÁO interactions as the pair of forceps-like tips at d e + d i $ 2.5 Å . A low percentage contribution due to OÁ Á ÁH/HÁ Á ÁO contacts is noted for (II), as research communications Acta Cryst. (2018). E74, 302-308 Mohamad et al. [Sn(C 4 H 9 ) 2 (C 7 H 14 NO 2 S 2 ) 2 ] and [Sn(C 6 H 5 ) 3 (C 5 H 10 NOS 2 )] 305 Table 5 Summary of short interatomic contacts (Å ) in (I).

Contact
Distance Symmetry operation Views of Hirshfeld surface for (I) mapped over d norm in the range À0.163 to +1.302, highlighting (a) and (b) intermolecular methylene-C-HÁ Á ÁO(methoxy) interactions and (c) short intra-layer HÁ Á ÁH contacts between methoxy-and butyl-hydrogen atoms H4B and H8A as sky-blue dashed lines.

Figure 5
Views of Hirshfeld surface mapped over the electrostatic potential (the red and blue regions represent negative and positive electrostatic potentials, respectively) for: (a) and (b) a molecule of (I) in the range À0.054 to +0.036 au and (c) a molecule of (II) in the range AE0.036 au.
summarized in Table 6. The relatively high, i.e. 29.1%, contribution from CÁ Á ÁH/HÁ Á ÁC contacts to the Hirshfeld surfaces of (II) is due to the presence of tin-bound phenyl substituents and the resulting short interatomic CÁ Á ÁH/HÁ Á ÁC contacts, Table 5, and intermolecular C-HÁ Á Á contact, Table 4, viewed as the pair of peaks at d e + d i $ 2.8 Å and the distribution of points around d e + d i $ 2.9 Å in both the wings of its delineated fingerprint plot, Fig. 7b. Although SÁ Á ÁH/ HÁ Á ÁS contacts have significant contributions to the Hirshfeld surfaces of (I) and (II), as summarized in Table 6, their interatomic distances are farther than sum of their van der Waals radii, i.e. d e + d i > 3.0 Å , Fig. 7, and hence do not have a structure-directing influence on the molecular packing. The small contributions from other contacts in (I) and (II) also have negligible impact in the respective crystals.

Database survey
It is well documented that organotin dithiocarbamates, R 00 x Sn(S 2 CNRR 0 ) 4-x , can adopt a variety of coordination geometries, especially for x = 2 (Tiekink, 2008). The structural motifs for the x = 2 series were recently summarized (Zaldi et al., 2017)  Views of the Hirshfeld surface for (II) mapped with the shape-index property showing (a) intermolecular C-HÁ Á Á/Á Á ÁH-C contacts and (b) short interatomic HÁ Á ÁH contacts through black-dashed lines.

Figure 7
Comparison of the full two-dimensional fingerprint plots for (I) and (II), and the plots delineated into (a) HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO and SÁ Á ÁH/HÁ Á ÁS contacts and (b) HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC and SÁ Á ÁH/HÁ Á ÁS contacts. trapezoidal bipyramidal geometry being observed in (I), this structure conforms to the common motif for the x = 2 structures. There is one other diorganotin structure with the same dithiocarbamate ligand, viz. the R 00 = C 6 H 5 compound . This, too, adopts the common trapezoidal bipyramidal geometry although a good number of other derivatives with R 00 = Ph adopt octahedral geometries, such as in (C 6 H 5 ) 2 Sn[S 2 CN(CH 3 )CH 2 CH 2 OCH 3 ] 2 (Muthalib et al., 2014) featuring the same dithiocarbamate ligand as in (II). The observed anisobidentate mode of coordination for the dithiocarbamate ligand in (II) is as expected and in fact is the norm for x = 3 structures which may be described as having 4 + 1 coordination geometries (Tiekink, 2008).

Synthesis and crystallization
All chemicals and solvents were used as purchased without purification. The melting points were determined using an automated melting point apparatus (MPA 120 EZ-Melt). Carbon, hydrogen, nitrogen and sulfur 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 at room temperature on Bruker AVANCE 400 lll HD in CDCl 3 . Synthesis of (I): bis(2-methoxyethyl)amine (Aldrich; 1.48 ml, 10 mmol) dissolved in ethanol (30 ml) was stirred for 30 min. Then, carbon disulfide (0.6 ml, 10 mmol) in cold ethanol was added and the resulting mixture was stirred for 2 h. A 25% ammonia solution (1-2 ml) was added to generate basic conditions. Then, di-n-butyltin(IV) dichloride (Aldrich; 1.52 g, 5 mmol) dissolved in ethanol (20-30 ml) was added dropwise into the solution and stirring was continued for 2 h. All reactions were carried out at 277 K. The precipitate that formed was dried and collected. Colourless prisms were harvested from the slow evaporation of its chloroform:ethanol 28.55 Sn-CH 2 CH 2 ; 26.41 Sn-CH 2 CH 2 CH 2 ; 13.87 CH 2 CH 3 . 119 Sn NMR (CDCl 3 ): À335.5.
Synthesis of (II): The synthesis of (II) was carried out in the same manner as for (I) using (2-methoxyethyl)methylamine (Santa Cruz Biotechnology; 1.1 ml, 10 mmol) and triphenyltin(IV) chloride (Merck; 3.85 g, 10 mmol). Crystallization in the form of colourless slabs was from its chloroform:ethanol

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 2.18 and 0.88 e Å À3 , respectively, were located 0.88 and 1.03 Å from the S1 and Sn atoms, respectively. For (II), the maximum and minimum residual electron density peaks of 2.21 and 1.82 e Å À3 , respectively, were located 0.96 and 0.76 Å from the Sn atom.

Bis[N,N-bis(2-methoxyethyl)dithiocarbamato-κ 2 S,S′]di-n-butyltin(IV) (I)
Crystal data [Sn(C 4  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 2.18 e Å −3 Δρ min = −0.88 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 2.18 and 0.88 eÅ -3 , respectively, were located 0.88 Å and 1.03 Å from the S1 and Sn atoms, respectively.

[N-(2-Methoxyethyl)-N-methyldithiocarbamato-κ 2 S,S′]triphenyltin(IV) (II)
Crystal data [Sn(C 6  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 2.21 and 1.82 eÅ -3 , respectively, were located 0.96 Å and 0.76 Å from the Sn atom.