Crystal structure of bis[S-hexyl 3-(4-methylbenzylidene)dithiocarbazato-κ2 N 3,S]nickel(II)

In the title complex, [Ni(C15H21N2S2)2], the NiII atom exhibits a square-planar coordination geometry and is located on an inversion centre leading to a trans configuration of the N,S-chelating ligands. In the crystal, the complex molecules stack at a distance of 4.6738 (3) Å along the a axis, which exclude any significant interactions between the aromatic rings.


S1. Structural commentary
The metal is located on a crystallographic inversion centre and the two Schiff bases, in their deprotonated imino thiolate form, act as chelating ligands to the metal centre via the azomethine nitrogen N1 and thiolate sulphur S1 atoms in a transplanar configuration as imposed by the crystal symmetry. The complex has coplanar geometry with the exception of the hexyl chains that pend hedgewise. In the complex, the Ni-S and Ni-N bond distances are of 2.1777 (11) and 1.933 (4) Å, respectively, with a S(2)-Ni-N(2) chelating angle of 86.06 (10)°. These geometrical parameters agree with those reported for similar nickel complexes either when ligands assume a trans (Islam, et al., 2011;Islam, et al., 2014;Zhang, et al., 2004) or a cis configuration (Chan, et al., 2008;Li, et al., 2006). The ligand, recently reported (Howlader, et al., 2015), underwent rotation about the C9-N2 by 180° in order to allow the N,S chelating behavior towards the metal.
Upon coordination some salient features are observed with respect to the free ligand, and the most significant are an elongation of the C(9)-S(1) bond length (1.720 (4) Å in NiL 2 that must be compared to 1.670 (3) Table 1).

S2. Supramolecular features
The complexes stack at a distance of 4.6738 (3) Å (axis a), which exclude any significant interactions between the aromatic rings.

S3. Synthesis and crystallization
A solution of Ni(CH 3 COO) 2 .4H 2 O (0.06 g, 0.25 mmol, 8 mL methanol) was added to a solution of the ligand, S-hexyl (E)-3-(4-methylbenzylidene)dithiocarbazate, (0.15 g, 0.5 mmol, 10 mL methanol ). The resulting mixture was stirred at room temperature for four hours. A dark reddish brown precipitate was formed, filtered off, washed with methanol and dried in vacuo over anhydrous CaCl 2 . Dark reddish brown single crystals, suitable for X-ray diffraction, of the compound were obtained by slow evaporation from a mixture of chloroform and acetonitrile (1:1) after 7 days. M.P. 374 K.

S4. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were located geometrically and treated as riding atoms, with C-H = 0.95-0.99 Å, and with Uĩso~(H) = 1.2U~eq~(C) or 1.5U~eq~(C) for methyl H atoms.  ORTEP drawing (ellipsoid probability at 50%) of the centrosymmetric NiL 2 complex.

Figure 2
Crystal packing of the complex.