Bis{(Z)-[(E)-2-(pyridin-2-ylmethylidene)hydrazin-1-ylidene][(pyridin-2-yl)methylsulfanyl]methanethiolato}nickel(II)

The title compound, [Ni(C13H11N4S2)2], was obtained by the reaction of S-2-picolyldithiocarbazate and pyridine-2-carbaldehyde with nickel(II) acetate. The NiII atom is located on a twofold rotation axis and is bonded to four N atoms at distances of 2.037 (8) and 2.109 (9) Å, and to two S atoms at a distance of 2.406 (3) Å, leading to a distorted octahedral coordination. The angle between the mean planes of the coordinating moieties of the two symmetry-related tridentate ligands is 83.3 (2)°. In the crystal, complex molecules are linked by weak C—H⋯S hydrogen bonds, π–π interactions between the pyridine rings [centroid–centroid distance = 3.775 (9) Å] and C—H⋯π interactions. The hydrogen-bonding interactions lead to the formation of layers parallel to (010); π–π interactions link these layers into a three-dimensional network.

The title compound, [Ni(C 13 H 11 N 4 S 2 ) 2 ], was obtained by the reaction of S-2-picolyldithiocarbazate and pyridine-2-carbaldehyde with nickel(II) acetate. The Ni II atom is located on a twofold rotation axis and is bonded to four N atoms at distances of 2.037 (8) and 2.109 (9) Å , and to two S atoms at a distance of 2.406 (3) Å , leading to a distorted octahedral coordination. The angle between the mean planes of the coordinating moieties of the two symmetry-related tridentate ligands is 83.3 (2) . In the crystal, complex molecules are linked by weak C-HÁ Á ÁS hydrogen bonds,interactions between the pyridine rings [centroid-centroid distance = 3.775 (9) Å ] and C-HÁ Á Á interactions. The hydrogenbonding interactions lead to the formation of layers parallel to (010);interactions link these layers into a threedimensional network.

Comment
In the last few decades an increasing interest in the potential benefits of dithiocarbazates has arisen which has led to the synthesis of several Schiff base ligands and complexes that can be derived from dithiocarbazates (Tarafder et al., 2002;Hossain et al., 1996). S-2-picolyl dithiocarbazate (S2PDTC) is one type of a dithiocarbazate compound that has been synthesized recently, and its Schiff bases and complexes have proven to possess antimicrobial and anticancer activities (Crouse et al., 2004). Due to these potential medicinal properties of S2PDTC-derived Schiff bases and complexes, the title compound was synthesized and structurally analyzed.
The angle between the mean plane defined by (Ni1-S2-C7-N2-N3-N4-C8) and that of the symmetry-related ligand is 83.3 (2)° which shows that the two ligands are nearly orthogonal to each other. The Ni-N bond lengths of the title complex are very similar to that of a previously reported related structure (Omar et al., 2012) [2.013 (2) Å for Ni-N, 2.179 (2) Å for Ni-N where this N atom belongs to the pyridine ring; 2.426 (7) Å for Ni-S] which might indicate that the values of such bond lengths are typical of nickel(II) complexes derived from dithiocarbazates. The pyridine ring (C1-C2-C3-C4-C5-N1) is nearly perpendicular to the rest of the molecule with a torsion angle of C5-C6-S1- The molecules in the crystal are stabilized by weak intermolecular C-H···S hydrogen bonding interactions (Table 1; parallel to each other and form π···π interactions (Fig. 3) with a centroid-centroid separation of 3.775 (9) Å and a shift distance of 1.878 (17) Å while the distance between the planes of the rings is 3.275 (12) Å. There are also C-H···π interactions (Table 1; Fig. 4).

Experimental
The nickel complex was synthesized according to a modified procedure reported by Crouse et al. (2004) of the mixture. The reactants were later mixed and 2-4 drops of concentrated H 2 SO 4 were added to the mixture followed by heating of the mixture for 5 minutes. The mixture was cooled to 273 K in an ice-bath until the precipitation of the Schiff base ligand was achieved, and this was followed by filtration of the precipitated Schiff base ligand via suction filtration, washing it with cold ethanol and drying over silica gel. 0.0076 mole of the synthesized Schiff base ligand were dissolved in 50 ml of absolute ethanol followed by the addition of an equimolar amount of KOH and the mixture was heated over a heating plate and stirred until the compounds had been completely dissolved. The solution was then treated with a stoichiometric amount of nickel(II) acetate (0.0038 moles) dissolved in 50 ml of absolute ethanol followed by heating for 5 minutes and then kept in an ice-salt bath. Finally, the obtained product was isolated via suction filtration, washed with ethanol and dried over silica gel.

Refinement
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-98 Å) and isotropic temperature factors (U iso (H) in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints.

Figure 1
The molecular structure of the title compound showing 50% probability displacement ellipsoids in addition to the atomic numbering scheme. Hydrogen atoms were omitted for clarity. The second ligand is related to the first by symmetry code x, -y, z + 1/2.  The molecules in the structure are stabilized by intermolecular C-H···S hydrogen bonding interactions. Probability function as in Fig. 1. [Symmetry code: (ii) x, -y, z + 1/2.]

Figure 3
The molecules in the structure are also linked by π···π interactions between pairs of pyridine rings with a centroid···centroid distance of 3.775 (9) Å. Probability function as in Fig. 1  Diagram showing the C-H···π interaction between the molecules in the structure. Probability function as in Fig. 1.