[μ2-trans-1,2-Bis(pyridin-4-yl)ethene-κ2 N:N′]bis{[1,2-bis(pyridin-4-yl)ethene-κN]bis[N-(2-hydroxyethyl)-N-isopropyldithiocarbamato-κ2 S,S′]cadmium} acetonitrile tetrasolvate: crystal structure and Hirshfeld surface analysis

A distorted octahedral cis-N2S4 coordination geometry is found in the title solvated bimetallic complex. The packing features supramolecular layers sustained by O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonding.

The asymmetric unit of the title compound, [Cd 2 (C 12 H 10 N 2 ) 3 (C 6 H 12 NOS 2 ) 4 ]Á-4C 2 H 3 N, comprises a Cd II atom, two dithiocarbamate (dtc) anions, one and a half trans-1,2-dipyridin-4-ylethylene (bpe) molecules and two acetonitrile solvent molecules. The full binuclear complex is generated by the application of a centre of inversion. The dtc ligands are chelating, one bpe molecule coordinates in a monodentate mode while the other is bidentate bridging. The resulting cis-N 2 S 4 coordination geometry is based on an octahedron. Supramolecular layers, sustained by hydroxy-O-HÁ Á ÁO(hydroxy) and hydroxy-O-HÁ Á ÁN(bpe) hydrogen bonding, interpenetrate to form a three-dimensional architecture; voids in this arrangement are occupied by the acetonitrile solvent molecules. Additional intermolecular interactions falling within the specified framework have been analysed by Hirshfeld surface analysis, includinginteractions.

Structural commentary
The molecular structure of the binuclear title compound, {Cd[S 2 CN(iPr)CH 2 CH 2 OH] 2 [(4-NC 5 H 4 )C C 6 H 4 N-4)]} 2 [(4-NC 5 H 4 )C C 6 H 4 N-4)]Á4CH 3 CN, (I), Fig. 1, is situated about a centre of inversion; two acetonitrile molecules of solvation complete the asymmetric unit. Each Cd II atom is coordinated by two dithiocarbamate ligands and two nitrogen atoms, one derived from a monodentate trans-1,2-dipyridin-4-ylethylene (bispyridylethene; bpe) ligand and another from one end of a bidentate, bridging bpe ligand (located about a centre of inversion). The dithiocarbamate ligands coordinate with significant differences in their Cd-S bond lengths, Table 1. Thus, Á(Cd-S) = d(Cd-S long ) -d(Cd-S short ) = 0.15 Å for the S1-dithiocarbamate ligand cf. 0.10 Å for the S3-ligand. Nevertheless, there is considerable delocalization of -elec-tron density in the CdS 2 C chelate rings as evidenced by the equivalence of the associated C-S bond lengths,

Figure 1
The molecular structure of the binuclear title compound in (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Unlabelled atoms are related by the symmetry operation (2 À x, Ày, 1 À z.). The acetonitrile solvent molecules have been omitted for clarity.

Supramolecular features
Geometric details of the significant intermolecular interactions are given in  Fig. 2c. The N7-acetonitrile molecule is connected to the host framework by pyridyl-C-HÁ Á ÁN(acetonitrile) interactions whereas the N6-acetonitrile molecule does not form significant interactions in accord with the criteria embodied in PLATON (Spek, 2009). This is reflected in the greater displacement ellipsoids for this molecule cf. with the N7-containing molecule. Further analysis of the molecular packing, e.g. pyridylÁ Á Ápyridyl interactions, is given in the following Section.

Figure 2
Molecular packing in (I): (a) view of the supramolecular ladder sustained by hydroxy-O-HÁ Á ÁO(hydroxy) hydrogen bonds, shown as orange dashed lines, (b) two-dimensional framework whereby the layers in (a) are connected by hydroxy-O-HÁ Á ÁN(bpe) hydrogen bonds, shown as blue dashed lines, (c) view of the unit-cell contents shown in projection down the a axis, highlighting the interpenetration of successive supramolecular layers, illustrated in orange and green, with solvent acetonitrile molecules shown in black.
trostatic potential, Fig. 4. The light-red spots near ethene-H25, pyridyl-C28 and hydroxy-O2 in Fig. 3 and near acetonitrile-N7, Fig. 5a, indicate their involvement in the intermolecular ethene-C-HÁ Á ÁO(hydroxy) and pyridyl-C-HÁ Á ÁN(acetonitrile) interactions. The presence of short intermolecular CÁ Á ÁC and CÁ Á ÁH contacts, Table 3, is also evident from the light-red spots appearing near the pyridyl-C16, C19 and C24 and methylene-H3A atoms in Fig. 3. The C18-C18 i link of the bridging bpe ligand can be viewed as a bright-red region around the C18 atom in the d norm mapped surface, Fig. 3, and as a light-blue region surrounded by a pair of light-red arcs on the surface mapped over electrostatic potential, Fig. 4b; this arises as it is the asymmetric unit that has been investigated not the entire binuclear molecule. With respect to the acetonitrile molecule the d norm mapped surfaces show only the acetonitrile-N7 to be involved in a significant intermolecular C-HÁ Á ÁN interaction (Fig. 5a, Table 2), and both acetonitrile molecules had very similar Hirshfeld surfaces mapped over electrostatic potential to that for the N7-molecule illustrated in Fig Table 3 Summary of short interatomic contacts (Å ).

Contact
Distance Symmetry Two views of the Hirshfeld surface mapped over d norm . The contact points (red) are labelled to indicate the atoms participating in the intermolecular interactions.

Figure 4
Two views of the Hirshfeld surface mapped over the electrostatic potential with positive and negative potential indicated in blue and red, respectively.
contributions are summarized in Table 4. The HÁ Á ÁH contacts make the greatest contribution to the Hirshfeld surface, i.e. 51.9% which is reflected in Fig. 6b as widely scattered points of high density due to the large hydrogen content of the molecule; the single peak at d e = d i $1.15 Å results from a short intermolecular HÁ Á ÁH contact between the isopropyl-H5A and pyridyl-H23 atoms, Table 3. In the fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts, the 6.0% contribution to the Hirshfeld surface arises from the intermolecular O-HÁ Á ÁO hydrogen bonding and is viewed as a pair of spikes with the tip at d e + d i $1.8 Å in Fig. 6c. The intermolecular C-HÁ Á ÁO interactions and short OÁ Á ÁH/HÁ Á ÁO contacts, listed in Table 3, are masked by the strong O-HÁ Á ÁO hydrogen bonding in this plot.
In the absence of C-HÁ Á Á interactions in the crystal, the pair of characteristic wings resulting in the fingerprint plot delineated into CÁ Á ÁH/HÁ Á ÁC contacts with 15.9% contribution to the Hirshfeld surface, Fig. 6d, and the pair of thin edges at d e + d i $2.7 Å result from short interatomic CÁ Á ÁH/HÁ Á ÁC contacts, Table 3. A pair of spikes at d e + d i $1.8 Å correspond to NÁ Á ÁH/HÁ Á ÁN contacts, Fig. 6e, confirm the presence of intermolecular O-HÁ Á ÁN and C-HÁ Á ÁN interactions. The CÁ Á ÁC contacts assigned to short interatomic C16Á Á ÁC19 and C16Á Á ÁC20 contacts listed in Table 3

Figure 5
A view of the (a) Hirshfeld surface mapped over d norm and (b) Hirshfeld surface mapped over the electrostatic potential with positive and negative potential indicated in blue and red, respectively, for the N7-acetonitrile molecule. actions within the three-dimensional architecture described in Supramolecular features appear as the two distinct distributions of points in Fig. 6f. The vertex at d e = d i = 1.6 Å in the approximately triangular distribution of points in the plot corresponds to short intermolecular CÁ Á ÁC contacts. The presence ofstacking interactions between the centrosymmetrically related N5-pyridyl rings [inter-centroid distance = 3.674 (2) Å , symmetry code: 3 À x, 1 À y, 2 À z] is reflected through the appearance of green points around d e = d i $1.8 Å , the red and blue triangle pairs on the Hirshfeld surface mapped with shape-index property identified with arrows in the image of Fig. 7, and in the flat region on the Hirshfeld surface mapped over curvedness in Fig. 8. Finally, the SÁ Á ÁH/ HÁ Á ÁS contacts in the structure with a 10.3% contribution to the surface has a nearly symmetrical distribution of points, Fig. 6g, with the tips at d e + d i $2.95 Å arising from the short interatomic SÁ Á ÁH/HÁ Á ÁS contacts listed in Table 3. An additional descriptor, the enrichment ratio (ER), may be calculated on the basis of Hirshfeld surface analysis (Jelsch et al., 2014). This provides further insight into the molecular packing as it indicates the relative propensities to form specific intermolecular interactions. The ER values for (I) are collected in Table 5. The ER value close to but slightly less than unity for HÁ Á ÁH contacts, i.e. 0.97, is in accord with expectation (Jelsch et al., 2014). The ER value of 1.36 for OÁ Á ÁH/HÁ Á ÁO contacts is in the expected 1.2-1.6 range and confirms the involvement of these atoms in the intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO interactions. The ER value of 1.20 resulting from the 6% of the surface comprising nitrogen atoms and the 10.6% contribution to the Hirshfeld surface from NÁ Á ÁH/HÁ Á ÁN contacts is due to the presence of O-HÁ Á ÁN hydrogen bonding and the C-HÁ Á ÁN(acetonitrile) interaction. The high enrichment ratio of 2.23 for the CÁ Á ÁC contacts reflects the formation of significantstacking interactions and short CÁ Á ÁC contacts as mentioned above. The ER value close to unity, i.e. 0.92, for CÁ Á ÁH/HÁ Á ÁC contacts shows their propensity to form short intermolecular CÁ Á ÁH/HÁ Á ÁC contacts. The ER values < 1 related to other contacts and low percentage contribution to the surface do not show any significance in the crystal packing.

Figure 7
View of Hirshfeld surface mapped with shape-index property. The pairs of red and blue regions, identified with arrows, indicatestacking interactions.

isopropyldithiocarbamato-κ 2 S,S′]cadmium} acetonitrile tetrasolvate:
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.43 e Å −3 Δρ min = −0.81 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.