Bis[S-octyl 3-(2-methylpropylidene)dithiocarbazato-κ2 N 3,S]nickel(II)

The bis-chelated mononuclear nickel(II) complex shows inversion symmetry, with the dithiocarbazato ligand in the usual trans configuration and the central metal cation in a square-planar coordination environment.

The central Ni II atom in the title complex, [Ni(C 13 H 25 N 2 S 2 ) 2 ], is located on an inversion center and adopts a roughly square-planar coordination environment defined by two chelating N,S donor sets of two symmetry-related ligands in a trans configuration.The Ni-N and Ni-S bond lenghts are 1.9193 ( 14) and 2.1788 (5) A ˚, respectively, with a chelating N-Ni-S bond angle of 86.05 (4) � .These data are compared with those measured for similar dithiocarbazato ligands that bear n-octyl or n-hexyl alkyl chains.Slight differences are observed with respect to the phenylethylidene derivative where the ligands are bound cis relative to one another.

Structure description
Dithiocarbazate Schiff base derivatives have emerged as prospective ligands in medicinal chemistry as a result of their various pharmaceutical and biological activities (Gou et al., 2022;Low et al., 2016;Malik et al., 2020).For some years, we have been undertaking a study of N,S-chelating dithiocarbazato ligands and their corresponding metal complexes, which were observed to crystallize with ligands both in trans and cis configurations (Begum et al., 2020).Considering the above aspects, and in a continuation of our research, we report herein a novel Ni II complex with a dithiocarbazato Schiff base ligand bearing an octyl alkyl chain.
In the title complex (Fig. 1), [Ni(C 13 H 25 N 2 S 2 ) 2 ], the Ni II atom is located on an inversion center and exhibits a square-planar coordination environment, defined by two negatively charged N,S-chelating ligands in a trans configuration.The Ni-N1 and Ni-S1 bond lengths are 1.9193 ( 14) and 2.1788 (5) A ˚, respectively, with a chelating N1-Ni-S1 bond angle of 86.05 (4) � .With the exception of methyl groups C1 and C2, all of the non-H atoms of the title complex are coplanar, with Ni1 (+0.16A ˚) and S1 (-0.15A ˚) deviating the most from the leastsquares plane (r.m.s.deviation of fitted atoms = 0.073 A ˚).The long alkyl chain is in a staggered conformation with torsion angles along the chain between 178.20 (19) and 179.81 (15) � .The molecular structure is stabilized by an intramolecular non-conventional C4-H4� � �S1 i hydrogen bond with a C4� � �S1 i distance of 3.0965 ( 16) A ˚and a C4-H4� � �S1 i angle of 121 � [symmetry code: A number of Ni II complexes with ligands bearing n-octyl or n-hexyl alkyl chains have been structurally characterized and a comparison of relevant bond lengths and angles is compiled in Table 1.The corresponding values reported above are consistent with those measured in bis-chelated Ni II complexes built with similar ligands bearing a methoxybenzylidene (Begum et al., 2018) or thiophenmethylidene (Khan et al., 2023a) ligand.On the contrary, in the phenylethylidene complex (Khan et al., 2023b) the two independent Ni-N bond lengths are 0.02 A ˚longer with respect to those calculated in the present work, while the Ni-S ones are shorter by ca 0.02 A ˚.It is worth noting that the latter complex exhibits a cis configuration of the ligands.A similar trend is also observed in the complex with the S-n-hexyl 3-(1-phenylethylidene)dithiocarbazate ligand (Begum et al., 2020).Nickel(II) and copper(II) complexes with dithiocarbazato ligands have been reported to crystallize in both cis and trans configurations,   Howlader et al., 2015); 5 (Begum et al., 2016); 6 (Begum et al., 2017); 7 (Begum et al., 2020).Complexes 3 and 7 show a cis configuration of ligands.(Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), DIAMOND (Brandenburg, 1999) and WinGX publication routines (Farrugia, 2012).

Figure 1
Molecular structure of the title complex [Ni(C 13 H 25 N 2 S 2 ) 2 ] with displacement ellipsoids drawn at the 50% probability level.
although the latter are slightly more frequent (Begum et al., 2020).However, the chelating N,S bond angles in these complexes are similar within their standard deviations and fall into the range 85.67 (5)-86.40(5) � .The packing of the complex is shown in Fig. 2; the complexes stack with an Ni� � �Ni separation of 7.8973 (2) A ålong the c axis.

Synthesis and crystallization
A solution of Ni(CH 3 COO) 2 •4H 2 O (0.124 g, 0.5 mmol) in 10 ml of methanol was added to a solution of S-octyl-3-(2methylpropylidene)dithiocarbazate (0.274 g, 1.0 mmol) in 30 ml of methanol.The resulting mixture was stirred at room temperature for 5 h.The green precipitate that formed was filtered off, washed with methanol and dried in vacuo over anhydrous CaCl 2 .Green single crystals of the title compound suitable for X-ray diffraction were obtained by slow evaporation from a mixture of chloroform and acetonitrile (1:1, v/v) after 7 d.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

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.

Figure 2
Figure 2 View of the crystal packing of the title complex [Ni(C 13 H 25 N 2 S 2 ) 2 ] in a view along [102]; H atoms are not shown for clarity.

Table 2
Experimental details.