{4-Phenyl-1-[1-(1,3-thiazol-2-yl)ethylidene]thiosemicarbazidato}{4-phenyl-1-[1-(1,3-thiazol-2-yl)ethylidene]thiosemicarbazide}nickel(II) chloride monohydrate

In the title compound, [Ni(C12H11N4S2)(C12H12N4S2)]Cl·H2O, the NiII ion is chelated by two 2-acetylthiazole-3-phenylthiosemicarbazone ligands, forming a distorted octahedral complex. The metal ion is coordinated via the thiazole nitrogen, imine nitrogen and thione sulfur atoms from each thiosemicarbazone ligand, and two coordinating units lie almost perpendicular to each other give dihedral angle = 81.89 (1)°]. One thiosemicarbazone unit is found to bind a chloride anion through two hydrogen bonds, while the other is linked with the disordered crystal water molecule. Two molecules are connected to each other through an intermolecular N—H⋯S interaction, forming a centrosymmetric dimer. Dimers are linked into sheets by π–π stacking of two phenyl rings [shortest C⋯C distance = 4.041 (3) Å].


Related literature
For general background to thiosemicarbazones and their metal complexes, see: Haiduc & Silverstru (1990); Nath et al.

Comment
Studies on thiosemicarbazones and their metal complexes remain an active field of research for more than three decades due to their significant impacts in biology and chemistry (Ali & Livingstone, 1974;Campbell, 1975;Haiduc & Silverstru, 1990;Nath et al., 2001;Padhye & Kauffman, 1985;Pellerito & Nagy, 2002). Thiosemicarbazones are also known to stabilize uncommon oxidation states of metals upon complexation. The variation of coordination numbers exhibited by transition metals in these complexes is utilized in various redox reactions and found to inhibit the activity of metalloenzymes. In particular, the characterization of the coordination aspects of metal complexes with thiosemicarbazone ligands are important in order to model the physical and chemical behaviour of metalloenzymes (Viñuelas-Zahínos et al. 2008). Nickel(II) complexes of heterocyclic thiosemicarbazones were previously reported by Ketcham et al. (2002) andde Lima et al. (1999). Recently, Barros-Garcia et al. (2005) studied the structural and ligation properties of 2-acetyl thiazole semicarbazone of nickel(II). In the present study, we report the synthesis and structure of nickel(II) complex of the phenyl derivative of 2-acetylthiazole-

3-thiosemicarbazone.
The title complex is a result of interaction between the neutral ligand molecules and nickel (II) ions in aqueous solution.
Indeed, the participation of sulfur groups as electron pair donors in coordinating Ni II ion makes the secondary amines more acidic which results the complete loss of one proton on N3 from one ligand. Interestingly, this nitrogen (N3) acts as a hydrogen bond acceptor for one water molecule (Table 1). On the other hand, the second ligand is involved in binding a chloride anion with two hydrogen bonds (NH···Cl = 3.2050 (15) and 3.1051 (16) Å, which are slightly shorter than 3.048 (3) Å observed in a cryptand based receptor binding a chloride anion in its cavity (Saeed et al., 2009). Additionally, the two neighboring molecules are found to form a centrosymmetric dimer through NH···S interactions (Fig. 2). In the packing diagram the dimers are again connected with π-π stacking of two phenyl rings (Fig. 3).
The structure contains an unreasonably short distance O1A···C17, 2.629 (18) Å. This distance involves an atom (O1A) which was treated as occupied <9%. Since the contact is to the average position of a fully-occupied atom (C17), the distance does not imply an actual contact between two atoms. After refinement of the ordered part of the structure, residual density of 1.08 eÅ -3 was located in a cavity slightly too small for occupancy by a water molecule. The site is 2.488 (17) Å from O1 (at 1-x, 1-y, 1-z), and is taken to be an alternate site for O1. Refinement with O1 and O1A having occupancies summing to unity led to occupancy of 0.087 (4) for O1A. The cavity likely expands when O1A is occupied, and the displacement parameters supplementary materials sup-2 of the atoms surrounding the cavity, including C17, support this interpretation. The environments of water molecule O1 and site O1A are quite different, the former engaging in long hydrogen bonds with N and Cl, while the latter is in a small void with no hydrogen bonding. This accounts for the large difference in the refined occupancies of the two sites. It appears unlikely that both sites could be simultaneously occupied, because of the short distance between them.

Experimental
The cationic nickel complex was prepared by adding an aqueous solution of nickel (II) chloride to a boiling methanolic solution of thiosemicarbazone (Venkatraman et al. 2009) in 1:2 mol ratio. Heating was continued for about 2 hours. Light brown colored crystals were obtained by evaporation of the solvent at room temperature (yield = 60%).

Refinement
H atoms on C were placed in idealized positions with C-H distances 0.95 -0.98 Å and thereafter treated as riding. The coordinates of those on N and O were refined. U iso for H was assigned as 1.2 times U eq of the attached atom (1.5 for methyl).
A torsional parameter was refined for each methyl group. A residual peak of density 1.08 eÅ -3 , with nearest distance 2.5 Å to the water position was interpreted as a disordered water site. The partially-occupied water site O1A was treated as isotropic, and its H atoms were not located. The largest residual density peak was 0.84 Å from S3. Fig. 1. Packing diagram of the title compound showing a molecular chain viewed along a axis.

Figures
Crystal data [Ni(C 12

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.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.