Crystal structure of S-n-octyl 3-(1-phenylethylidene)dithiocarbazate and of its bis-chelated nickel(II) complex

A bis-chelated mononuclear nickel(II) complex with a dithiocarbazate ligand bearing a long saturated alkyl chain exhibits a distorted cis square planar coordination of the metal with two ligands conformationally different from the proligand.


Chemical context
Bidentate Schiff bases of S-methyl dithiocarbazate (SMDTC) or S-benzyl dithiocarbazates (SBDTC) and their bivalent metal complexes have received considerable attention in the field of medical science for their biological activities (Cavalcante et al., 2019;Chan et al., 2008;Chew et al., 2004;Crouse et al., 2004;How et al., 2008;Yang et al., 2020).As part of our ongoing interest in S-containing Schiff bases and the corresponding metal complexes, we report herein on the structure of a ligand molecule having an octyl alkyl chain and of its bischelated nickel complex.

Structural commentary
The HL proligand crystallizes in its thione tautomeric form (Fig. 1).The �-N atom (N1) and the thioketo atom S1 are located in trans positions with respect to the C9-N2 bond, as has been observed in other similar dithiocarbazate species (Begum et al., 2015).The phenyl ring is disordered with equal probability between two orientations, differing by a dihedral angle of 42.2 (3) � .The adjacent methyl group C8H 3 is likewise disordered, the directions of the C7-C8 bond differing by 23.1 (1) � .While there can be some ambiguity on how the disorder of the phenyl and methyl groups is correlated intramolecularly, we suggest that the near-eclipsed conformation about the C1-C7 bond (as shown here) is more likely than the alternative one (twisted by 31 or 38 � ), because the former conformation was typically observed in previously studied compounds of ArC(Me) NNHC( S)SR type, where Ar is a phenyl group or a phenyl substituted in a meta or para (but not ortho) position (see Section 4).
In the NiL 2 complex (Fig. 2) the two Schiff bases L in their deprotonated imino thiolate form, coordinate the metal through the �-nitrogen atoms, N1 or N3, and the thiolate sulfur, S1 or S3, respectively, in a cis-square-planar configuration which is tetrahedrally distorted in order to avoid steric clashes between the phenyl rings.The dihedral angle formed by the NiNS planes of the two five-membered chelate rings is thus 21.66 (6) � .The Ni-S bond distances of 2.1506 (6) and 2.1573 (6) A ˚are similar, as are the Ni-N ones of 1.9392 ( 16) and 1.9318 (15) A ˚.The orientation of the phenyl groups is such that their ortho hydrogen atoms are located in apical positions above and below the metal centre, with the Ni� � �H separations of ca 2.6 A ˚indicating possible non-covalent interactions.
Some important geometrical changes are observed in the ligand upon coordination, the most significant being the elongation of the S1 C9 bond of 1.669 (3) A ˚in HL to the essentially single bonds of 1.738 (2) A ˚in the complex, thus validating the coordination with deprotonated thiolate sulfur atom.Correspondingly the N2-C9 bond of 1.340 (4) A ˚in HL shortens to essentially double bonds of 1.293 (3) and 1.290 (2) A ˚in the complex, while the N1-N2 bond length of 1.377 (4) A ˚is slightly elongated in the complex [to 1.414 (2) and 1.417 (2) A ˚, see the supporting information].These parameters agree with those in previously reported Ni II complexes with similar ligands (Begum et al., 2016(Begum et al., , 2017(Begum et al., , 2020(Begum et al., , 2023;;Howlader et al., 2015;Islam et al., 2014;Khan et al., 2023;Zangrando et al., 2015).Upon coordination the ligand L undergoes a rotation of ca.180 � about the N2-C9 bond to chelate the metal through the N and S donors.
The n-octyl chain in HL has an extended all-trans conformation and is practically coplanar with the dithiocarbazate moiety.In the complex, one n-octyl chain (C27 to C34) also adopts an all-trans conformation (although tilted out of the coordination plane), while the other one is 'kinked' due to the gauche conformation about the C13-C14 bond.
An analysis of dithiocarbazate ligands in bis-chelated Ni and Cu complexes of cis and trans arrangement was reported by us earlier (Begum et al., 2020).Among the Ni II complexes with dithiocarbazate Schiff base N,S-ligands having long alkyl chains, the cis configuration was observed in derivatives with a phenylethylidene fragment bound at N1 (Zangrando et al., 2015;Begum et al., 2020), as in the present complex.

Supramolecular features
The crystal pacing of HL is shown in Fig. 3.The crystal structure contains segregated regions of polar dithiocarbazate moieties, hydrophobic alkyl chains and aromatic phenyl groups.
It is noteworthy that there are some sterically impossible short distances between symmetry-related positions of the disordered phenyl rings, e.g.C2� � �C2 of 2.72 A ˚between molecules related by an inversion centre, and C2A� � �C5A of 2.82 A ˚between molecules related by the translation a.Obviously, these orientations cannot be adopted by adjacent molecules simultaneously and the respective symmetry operations are locally spurious.
The packing of NiL 2 is shown in Fig. 4; the cis coordination does not allow the molecules to stack at short distances as  observed for trans square-planar species with analogous ligands (Howlader et al., 2015;Begum et al., 2016).

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 1.The phenyl ring of the uncoordi-  nated ligand was found disordered over two positions with equal (0.5) occupancies.All H atoms were geometrically located with exception of that at N2 in the free ligand which was freely refined.

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.

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 2Molecular structure of the NiL 2 complex.Atomic displacement ellipsoids are drawn at the 50% probability level.

Figure 1
Figure 1Molecular structure of HL.Atomic displacement ellipsoids are drawn at the 50% probability level.

Figure 4
Figure 4View of the crystal packing of the NiL 2 complex down the b axis (H atoms not shown for clarity).

Figure 3
Figure 3Crystal packing of HL viewed down the a axis (H atoms omitted and only one orientation of the disordered phenyl rings is shown for clarity).

Table 1
Experimental details.