Bis(μ2-N-methyl-N-phenyldithiocarbamato)-κ3 S,S′:S;κ3 S:S,S′-bis[(N-methyl-N-phenyldithiocarbamato-κ2 S,S′)cadmium]: crystal structure and Hirshfeld surface analysis

With both chelating and μ2-tridentate dithiocarbamate ligands, the structure of [Cd2(C8H8NS2)4] is a centrosymmetric dimer. The packing features C—H⋯S and C—H⋯π interactions.


Chemical context
The structural chemistry of the binary zinc-triad (group 12) dithiocarbamates ( À S 2 CNRR 0 ) 2 (R/R 0 = alkyl/aryl), along with related 1,1-dithiolate ligands, i.e. dithiophosphates [ À S 2 P(OR) 2 ] and dithiocarbonates (xanthates; À S 2 COR), have long attracted the attention of structural chemists owing to their diversity of structures/supramolecular association patterns in the solid state (Cox & Tiekink, 1997;Tiekink, 2003). The common structural motif adopted by all elements is one that features two chelating ligands and two tridentate ligands (chelating one metal atom and simultaneously bridging to a second), leading, usually, to a centrosymmetric binuclear molecule. Indeed, most zinc dithiocarbamate structures adopt this motif, but when the R/R 0 are bulky, a mononuclear species with tetrahedrally coordinated zinc atoms is found; significantly greater structural variety has been noted for the binary zinc dithiophosphates and xanthates (Lai et al., 2002;Tan et al., 2015). More diversity in structural motifs is noted in the binary cadmium dithiocarbamates with the recent observation of linear polymeric forms with hexacoordinated cadmium atoms (Tan et al., 2013(Tan et al., , 2016Ferreira et al., 2016). Systematic studies indicated solvent-mediated transformations between polymeric and binuclear structural motifs, with the latter being the thermodynamically more stable (Tan et al., 2013(Tan et al., , 2016. The greatest structural diversity among the zinc-triad dithiocarbamates is found for the binary mercury compounds, where mononuclear, binuclear and polymeric structures have been observed, as summarized very recently (Jotani et al., 2016). Complementing the structural motifs already mentioned for zinc and cadmium is a trinuclear species, {Hg[S 2 CN(tetra- ISSN 2056-9890 hydroquinoline)] 2 } 3 (Rajput et al., 2014), with the central Hg II atom being hexacoordinated, as in the polymeric form, and the peripheral Hg II atoms being coordinated as in the binuclear form, indicating the possibility that this is an intermediate metastable form in the crystallization of this compound. In light of the above, when crystals of the title compound became available, namely {Cd[S 2 CN(Me)Ph] 2 } 2 , (I), its crystal and molecular structures were studied, along with an evaluation of the supramolecular association in the crystal through an analysis of the Hirshfeld surface.
The resultant S 5 donor set defines a highly distorted pentacoordinate geometry, with the major distortions due to the disparate Cd-S bond lengths and the acute angles subtended at the Cd II atom by the chelating ligands ( The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. The molecule is located about a centre of inversion and unlabelled atoms are generated by the symmetry operation (Àx, 1 À y, 1 À z). Symmetry code: (i) Àx; Ày þ 1; Àz þ 1. Table 2 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the unit-cell contents of (I) in projection down the b axis. The C-HÁ Á Á(chelate ring) and C-HÁ Á ÁS interactions are shown as purple and orange dashed lines, respectively. geometry from the ideal square-pyramidal and trigonalbipyramidal geometries is given by the value of (Addison et al., 1984), which computes to 0.0 and 1.0 for the ideal geometries, respectively. In (I), the value of is 0.39, i.e. intermediate between the two extremes, but tending towards the former.

Supramolecular features
Two specific intermolecular interactions have been identified in the molecular packing of (I), and each involves the participation of phenyl ring C3-C8 (Table 2). Phenyl-C-HÁ Á Á interactions with the C3-C8 ring as the acceptor lead to supramolecular layers parallel to (102), as each binuclear molecule participates in four such interactions. The layers are connected into a three-dimensional architecture by phenyl-C-HÁ Á ÁS interactions, i.e. with the C3-C8 ring as donor (Fig. 2).

Hirshfeld surface analysis
The Hirshfeld surface analysis for (I) was performed as described in a recent report of a related binuclear cadmium dithiocarbamate compound (Jotani et al., 2016). On the Hirshfeld surface mapped over d norm in the range À0.055 to 1.371 au (Fig. 3), the bright-red spots near the C5, H5 and S1 atoms indicate respective donors and acceptors of intermolecular C-HÁ Á ÁS interactions; the other pair of faint-red spots near atoms C4 and S1 represent a weaker interaction ( Table 3). The donors and acceptors of the specified C-HÁ Á ÁS and C-HÁ Á Á interactions in Table 2, and short interatomic CÁ Á ÁH/HÁ Á ÁC contacts (Table 3)  A view of the Hirshfeld surface for (I) mapped over d norm in the range À0.055 to 1.371 au. Table 3 Short interatomic contacts (Å ) in (I).

Figure 4
A view of Hirshfeld surface for (I) mapped over the electrostatic potential in the range AE0.048 au.

Figure 5
Views of the Hirshfeld surface mapped over (a) d norm about a reference molecule, highlighting the intermolecular C-HÁ Á ÁS interactions and short interatomic CÁ Á ÁC contacts as black and red dashed lines, respectively, and (b) with shape-index property about a reference molecule. The C-HÁ Á Á and Á Á ÁH-C interactions are indicated with red and white dotted lines, respectively. and red regions on Hirshfeld surface mapped over electrostatic potential (in the range AE0.048 au) (Fig. 4). The immediate environments about a reference molecule within d norm and shape-index mapped Hirshfeld surface are illustrated in Figs. 5(a) and 5(b), respectively, and again highlight the influence of C-HÁ Á ÁS interactions, short C10Á Á ÁC15 contacts and C-HÁ Á Á interactions involving phenyl rings (atoms C3-C8) as the acceptor. Thus, the C-HÁ Á ÁS interactions involving the phenyl-ring C4, C5 and H5 atoms with S1 are shown with black dashed lines in Fig. 5(a); the red dashed lines indicate short interatomic CÁ Á ÁC contacts (Table 3). The C-HÁ Á Á and their reciprocal contacts, i.e. Á Á ÁH-C, with phenyl-ring atom C14 as donor and phenyl ring C3-C8 as acceptor, are shown with red and white dotted lines, respectively, on the Hirshfeld surface mapped with shape-index property in Fig. 5(b). The overall two-dimensional fingerprint plot and those delineated into HÁ Á ÁH, SÁ Á ÁH/HÁ Á ÁS, CÁ Á ÁH/HÁ Á ÁC and SÁ Á ÁS contacts (McKinnon et al., 2007) are illustrated in Figs. 6(a)-(e); their relative contributions to the Hirshfeld surface are summarized quantitatively in Table 4. The relatively low contribution of HÁ Á ÁH contacts to the Hirshfeld surface results from the involvement of surface H atoms in intermolecular C-HÁ Á ÁS, C-HÁ Á Á and CÁ Á ÁH/HÁ Á ÁC contacts. It is apparent from the fingerprint plot delineated into HÁ Á ÁH contacts (Fig. 6b) that HÁ Á ÁH contacts do not exert much influence on the molecular packing, as their interatomic distances are greater than the sum of their van der Waals radii, i.e. d e + d i > 2.8 Å . A pair of peaks appearing in the fingerprint plot delineated into SÁ Á ÁH/HÁ Á ÁS contacts at d e + d i $ 2.8 Å (Fig. 6c) arise from the C5-H5Á Á ÁS1 interaction; the weaker C4Á Á ÁH4Á Á ÁS1 interaction and short interatomic HÁ Á ÁS/SÁ Á ÁH contacts involving the S3 atom (Table 3) are viewed as a pair of thin green lines aligned at d e + d i $ 2.9 Å .
The distribution of points showing the superimposition of a forceps-like shape on characteristic wings in the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts (Fig. 6d) indicate the significance of these contacts through the presence of C-HÁ Á Á interactions and short interatomic CÁ Á ÁH/HÁ Á ÁC contacts in the crystal. A pair of green lines within the forceps also indicates the influence of these contacts. Finally, an arrowshaped distribution of green points in the centre in the plot corresponding to SÁ Á ÁS contacts (Fig. 6e), together with the contribution from CdÁ Á ÁS/SÁ Á ÁCd contacts to the Hirshfeld surface (Table 4), show the presence of intramolecularstacking interactions between the Cd/S1/C1/S2 chelate rings of inversion-related molecules [CgÁ Á ÁCg = 3.6117 (11) Å ; symmetry code: Àx, 1 À y, 1 À z]. The small contributions from CdÁ Á ÁH/HÁ Á ÁCd and NÁ Á ÁH/HÁ Á ÁN contacts (Table 4) do not impact significantly on the molecular packing.

Synthesis and crystallization
All chemicals and solvents were used as purchased without purification, and 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 PerkinElmer Spectrum 400 FT Mid-IR/Far-IR spectrophotometer from 4000 to 400 cm À1 . 1 H and 13 C NMR spectra were recorded at room temperature in DMSO-d 6 solution on a Jeol ECA 400 MHz FT-NMR spectrometer. Sodium methylphenyldithiocarbamate (1.0 mmol, 0.205 g) in methanol (25 ml) was added to cadmium chloride (1.0 mmol, 0.183 g) in methanol (10 ml). The resulting mixture was stirred and refluxed for 2 h. The filtrate was evaporated until an off-white precipitate was obtained, which was recrystallized in methanol. Slow evaporation of the filtrate yielded colourless crystals of the title compound

Bis(µ 2 -N-methyl-N-phenyldithiocarbamato)-κ 3 S,S′:S;κ 3 S:S,S′-bis[(N-methyl-N-phenyldithiocarbamatoκ 2 S,S′)cadmium(II)]
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.