Bis[N-2-hydroxyethyl,N-methyldithiocarbamato-κ2 S,S)’-4-{[(pyridin-4-ylmethylidene)hydrazinylidene}methyl]pyridine-κN 1)zinc(II): crystal structure and Hirshfeld surface analysis

The mononuclear title compound features a Zn2+ ion coordinated by two symmetrically binding dithiocarbamate ligands and one end of a 4-pyridinealdazine molecule with the resulting NS4 donor set tending towards a square-pyramidal geometry.

In the title compound, [Zn(C 4 H 8 NOS 2 ) 2 (C 12 H 10 N 4 )], the Zn II atom exists within a NS 4 donor set defined by two chelating dithiocarbamate ligands and a pyridyl-N atom derived from a terminally bound 4-pyridinealdazine ligand. The distorted coordination geometry tends towards square-pyramidal with the pyridyl-N atom occupying the apical position. In the crystal, hydroxyl-O-HÁ Á ÁO(hydroxyl) and hydroxyl-O-HÁ Á ÁN(pyridyl) hydrogen-bonding give rise to a supramolecular double-chain along [110]; methyl-C-HÁ Á Á(chelate ring) interactions help to consolidate the chain. The chains are connected into a threedimensional architecture via pyridyl-C-HÁ Á ÁO(hydroxyl) interactions. In addition to the contacts mentioned above, the Hirshfeld surface analysis points to the significance of relatively weakinteractions between pyridyl rings [inter-centroid distance = 3.901 (3) Å ].
By contrast to the chemistry described above for cadmium dithiocarbamates, no polymeric structures have been observed for zinc analogues with potentially bridging bipyridyl molecules. Instead, only binuclear compounds of the general formula [Zn(S 2 CNRR 0 ) 2 ] 2 (NN), i.e. R = CH 2 CH 2 OH and R 0 = Me, Et or CH 2 CH 2 OH for NN = 4,4 0 -bipyridyl (Benson et al., 2007), R = R 0 = CH 2 CH 2 OH and NN = pyrazine (Jotani et al., 2017), and R = CH 2 CH 2 OH and R 0 = Me for NN = (3-pyridyl)- (Poplaukhin & Tiekink, 2010) and Y = S (Poplaukhin et al., 2012). There are also several all-alkyl species adopting the binuclear motif with a notable example being the product of the reaction of [Zn(S 2 CNR 2 ) 2 ] 2 with an excess of 1,2-bis(4pyridyl)ethylene in which the binuclear species co-crystallized with an uncoordinated molecule of 1,2-bis(4-pyridyl)ethylene . This difference in behaviour, i.e. polymer formation for cadmium but not for zinc dithiocarbamates, is explained in terms of the larger size of cadmium versus zinc, which enables cadmium to increase its coordination number. In continuation of our studies in this area, the title compound, Zn[S 2 CN(Me)CH 2 CH 2 OH)] 2 (4-pyridinealdazine), (I), was isolated and shown to feature a terminally bound 4-pyridinealdazine ligand. Herein, its crystal and molecular structures are described as is an analysis of the calculated Hirshfeld surface.

Structural commentary
The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. The zinc(II) atom is coordinated by two chelating dithiocarbamate ligands and a nitrogen atom derived from a monodentate 4-pyridinealdazine ligand. There are relatively small differences in the The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Zn-S bond lengths formed by each dithiocarbamate ligand, i.e. ÁZn-S = (Zn-S long À Zn-S short ) = 0.10 Å for the S1dithiocarbamate ligand which increases to ca 0.12 Å for the second ligand. This symmetric mode of coordination is reflected in the equivalence of the associated C-S bond lengths. The resulting NS 4 donor set is highly distorted as shown by the value of of 0.32 which is intermediate between ideal square-pyramidal ( = 0.0) and trigonal-bipyramidal ( = 1.0) geometries (Addison et al., 1984) but, with a tendency towards the former. In the square-pyramidal description, the zinc(II) centre lies 0.7107 (7) Å out of the plane defined by the four sulfur atoms [r.m.s. deviation = 0.1790 Å ] in the direction of the pyridyl-N atom. The dihedral angle between the best plane through the four sulfur atoms and the coordinating pyridyl residue is 84.82 (9) , consistent with a nearly symmetric perpendicular relationship. The 4-pyridinealdazine molecule has an all-trans conformation and is essentially planar as seen in the dihedral angle of 2.7 (3) formed between the rings.

Supramolecular features
Both conventional and non-conventional hydrogen-bonding interactions feature in the crystal of (I),    Table 2 Hydrogen-bond geometry (Å , ).

Hirshfeld surface analysis
Additional insight into the intermolecular interactions influential in the crystal of (I) was obtained from an analysis of the Hirshfeld surfaces which were calculated in accord with a recent publication on related zinc dithiocarbamate compounds (Jotani et al., 2017). On the Hirshfeld surface mapped over d norm , Fig. 3, the donors and acceptors of the O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen-bonds are viewed as brightred spots near hydroxyl-H1O, H2O, hydroxyl-O2 and pyridyl-N6 atoms, located largely at the extremes of the molecule. The presence of bright-red spots near the H1O and H2O atoms in Fig. 3 are also indicative of short inter-atomic HÁ Á ÁH and CÁ Á ÁH/HÁ Á ÁC contacts, see Table 3. The diminutive-red spots near the methyl-C14, sulfur-S4, pyridyl-H20 and hydroxyl-O1 atoms characterize the influence of short inter-atomic CÁ Á ÁS/ SÁ Á ÁC contacts, Table 3, and intermolecular pyridine-C20-H20Á Á ÁO1 interactions. The donors and acceptors of the above intermolecular interactions are also represented with blue and red regions on the Hirshfeld surface mapped over electrostatic potential shown in   Table 3 Summary of short inter-atomic contacts (Å ) in (I).

Contact
Distance Symmetry operation

Figure 3
Two views of the Hirshfeld surface for (I) mapped over d norm in the range À0.400 to 1.552 au.

Figure 4
Two views of the Hirshfeld surface for (I) mapped over the electrostatic potential in the range AE0.151 au. The red and blue regions represent negative and positive electrostatic potentials, respectively.  The full two-dimensional fingerprint plot for (I) and fingerprint plots delineated into ( Fig. 6c, are due to the presence of some short inter-atomic contacts involving these atoms, Table 3. The effect of the intermolecular C-HÁ Á Á(chelate) interactions is also reflected by the short interatomic contacts formed by the methylene-C6 with the Zn atom, and methylene-H6B with the Zn, S1 and C1 atoms of the chelate ring, Fig. 6c, 6e, 6i, and  Table 3, are merged within the plot in Fig. 6d. The pattern of aligned green points superimposed on the forceps-like distribution of blue points in the SÁ Á ÁH/HÁ Á ÁS delineated fingerprint plot in Fig. 6e characterize the presence of short interatomic SÁ Á ÁH/HÁ Á ÁS contacts, Table 3, and C-HÁ Á Á (chelate) interactions, Fig. 5c. The C-HÁ Á ÁO interactions appear as the distribution of points in the short parabolic form attached to each of the spikes on the outer side of fingerprint plot delineated into OÁ Á ÁH/HÁ Á ÁO contacts, Fig. 6f, with (d e + d i ) min $ 2.3 Å . The parabolic distribution of points in the (d e = d i ) $ 1.8-2.0 Å range in the fingerprint plot delineated into CÁ Á ÁC contacts, Fig. 6g, indicate the existence of weakstacking interactions between the pyridyl-(N3,C9-C13) and (N6, C15-C20) i rings [CgÁ Á ÁCg i = 3.901 (3) Å ; symmetry code: (i) = x, 1 + y, z]. This observation is also viewed as the flat region around these rings in the Hirshfeld surfaces mapped over curvedness in Fig. 7. Both the CÁ Á ÁS/SÁ Á ÁC and ZnÁ Á ÁH/ HÁ Á ÁZn contacts make small but discernible contributions of 1.2 and 0.6% to the Hirshfeld surface, respectively, which are manifested as the pair of the short spikes in the centre of Fig. 6h, with their tips at d e + d i $ 3.2 Å , and wings in Fig. 6i. The low contribution from other contacts summarized in Table 4 have no significant influence on the molecular packing owing to their long separations.  (Shoshnik et al., 2005). In summary, the 4-pyridinealdazine molecule is usually found to be bridging, a conclusion vindicated by this mode of coordination being observed in about 95% of structures having 4-pyridinealdazine. While one might be tempted to ascribe the unusual behaviour of 4-pyridinealdazine in (I) and the cadmium(II) analogue to the influence of hydrogen-bonding associated with the dithiocarbamate ligand, it is salutatory to recall that the sole example of a monodentate bipyridyl ligand is found in the structure of Zn[S 2 CN(n-Pr) 2 ] 2 (4,4 0 -bipyridyl) (Klevtsova et al., 2001), where there is no possibility of conventional hydrogenbonding interactions; the binuclear species, {Zn[S 2 CN(n-Pr) 2 ] 2 } 2 (4,4 0 -bipyridyl), was characterized in the same study.

ylmethylidene)hydrazinylidene}methyl]pyridine-κN 1 )zinc(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )