Bis(μ-N,N-diallyldithiocarbamato)bis[(N,N-diallyldithiocarbamato)cadmium]

The characteristic feature of this cadmium(II) complex is the formation of a dimeric bridged structure where the two CdII cations are bridged by S atoms from the N,N-diallylldithiocarbamate ligands.

The title compound, [Cd 2 (C 7 H 10 NS 2 ) 4 ], is a neutral dinuclear cadmium(II) complex bearing four bis N,N-diallyldithiocarbamate ligands coordinating to two Cd II cations. In each of the monomeric subunits, there are four S atoms of two dithiocarbamate ligands [Cd-S = 2.5558 (3), 2.8016 (3), 2.6050 (3) and 2.5709 (3) Å ] that coordinate to one Cd II atom in a bidentate mode. The dimers are located over an inversion centre bridged by two additional bridging Cd-S bonds [2.6021 (3) Å ], leading to a substantial distortion of the geometry of the monomeric subunit from the expected square-planar geometry. The fivecoordinate environment around each of the Cd II ions in the dimer is best described as substantially tetragonally distorted square pyramidal. The dithiocarbamate groups are themselves planar and are also coplanar with the Cd II ions. The negative charge on these groups is delocalized by resonance across the S atoms bound to the Cd II cation. This delocalization of the electrons in the dithiocarbamate groups also extends to the C-N bonds as they reveal significant double bond character [C-N = 1.3213 (16) and 1.3333 (15) Å ].

Chemical context
Interest in the study of metal dithiocarbamates was aroused because of their interesting structural features and diverse applications (Thammakan & Somsook, 2006). Dithiocarbamate complexes have largely been prepared from the group 12 elements, mostly because they have found wide practical application as additives to pavement asphalt, as antioxidants, and as potent pesticides etc (Subha et al., 2010). The structural chemistry of cadmium dithiocarbamates of the general formula Cd(S 2 CNRR 0 ) where R, R 0 = alkyl or aryl is dominated by its existence in binuclear form. This common feature has been ascribed to the effect of aggregated species, which they adopt in the solid state, resulting from equal numbers of 2 -tridentate and bidentate (chelating) ligands (Tiekink, 2003;Tan, Halim et al., 2016). Only a few exceptions have been reported where the complex exists in a trinuclear form (Kumar et al., 2014), or as a one-dimensional polymeric motif (Tan et al., 2013(Tan et al., , 2016Ferreira et al., 2016). Bis(N,Ndiallyldithiocarbamato)cadmium compounds have the advantage of having stability similar to that of the zinc complexes, but more favourable stability when compared to the mercury complexes. Cadmium dithiocarbamate complexes have been widely used as single-source precursors for CdS ISSN 2056-9890 nanoparticles and thin films, which have application as nonlinear optical materials (Thammakan & Somsook, 2006). Another important practical application of cadmium dithiocarbamates is their ability to efficiently collect gold from acidic solutions (Rodina et al., 2014). Here we describe the crystal structure of a Cd II complex bearing a diallyldithiocarabamate ligand in a chelating and bridging dimeric structure.

Structural commentary
The coordination environment of the Cd II cation is observed to have a distorted tetragonal-pyramidal geometry (Fig. 1). The Cd II cation is coordinated by four S atoms with distances ranging from 2.5558 (3) to 2.8016 (3) Å and to a fifth S atom at a distance of 2.6021 (3) Å ; these distances are similar to other complexes found to have been published previously (see Section 4: Database survey). A full geometry check carried out with the Mogul Geometry Check tool (Bruno et al., 2004) within the CSD suite of programs, showed no unusual geometrical parameters. The fifth S atom, S12 i , is from a third ligand that is in the coordination sphere of a centrosymmetrically related Cd II ion [symmetry code: (i) -x + 2, -y, -z + 1]. This means that each bridging S atom simultaneously occupies an equatorial coordination site on one Cd II ion and an apical site on the other Cd II ion to form an edge-shared tetragonalpyramidal geometry. The Cd II ion deviates from the S11-S12-S22-S21 mean plane by 0.704016 (17) Å towards S12 i . The bridging network Cd1-S12-Cd1 i -S12 i is completely planar since it lies over the inversion centre with a Cd1Á Á ÁCd1 i separation distance of 3.60987 (8) Å and S12-Cd1-S12 i and Cd1-S12-Cd1 i angles of 96.257 (9) and 83.743 (9) , respectively. There is substantial distortion of the geometry of the monomeric subunit from the expected square-planar geometry. Deviations from the standard 90 angles are evident in the angles of S11-Cd1-S21 [108.203 (11) ]; S22-Cd1-S21 [70.264 (10) ]; S22-Cd1-S12 [96.950 (10) ] and S11-Cd1-S12 [67.486 (10) ]. Deviations in the standard 180 angles are evident in the angles of S11-Cd1-S22 [143.705 (13) ] and S21-Cd1-S12 [152.651 (11) ]. The Cd1-S12-Cd1 i -S12 i and S11-S12-S22-S21 mean planes form a dihedral (twist) angle of 84.6228 (18) . The dithiocarbamate groups are planar and each group of the monomeric subunit is coplanar with the Cd II ion (r.m.s. deviation is 0.010 Å ). The mean plane consisting of atoms Cd1, S11, N1, C11, S12 and the mean plane consisting of atoms Cd1, S22, N2, C21, S21 have a plane-normal-to-plane-normal angle of 37.0291 (10) ; a centroid-to-centroid distance of 4.45354 (8) Å ; a plane-to-plane shift of 4.22298 (8) Å and a plane-to-plane torsion (twist) angle of 8.0304 (12) .

Figure 2
The crystal structure of the title compound constructed from chains formed by C-HÁ Á ÁS interactions (red dashed lines). [Authors: Please add unit cell outline and coordinate axes] NMR data) has been published previously (Onwudiwe et al., 2015).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were positioned geometrically and refined isotropically using the riding-model approximation with C-H = 0.99 Å and U iso (H) = 1.2 U eq (C) for methylene groups and C-H = 0.95 Å and U iso (H) = 1.2 U eq (C) for all vinyl groups. program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: PLATON (Spek, 2009) and Mercury (Macrae et al., 2008).

Bis(µ-N,N-diallyldithiocarbamato)bis[(N,N-diallyldithiocarbamato)cadmium]
Crystal data Extinction correction: SHELXL2017 (Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0173 (7) 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. Carbon-bound H atoms were placed in calculated positions and were included in the refinement in the riding model approximation, with U(H) set to 1.2 U eq (C). Two reflections with large differences between their observed and calculated intensity were omitted. This is probably due to obstruction by the beam stop.