[1-(5-Bromo-2-oxidobenzylidene)thiosemicarbazidato-κ3 O,N 1,S](pyridine-κN)nickel(II)

The reaction of 5-bromosalicylaldehyde thiosemicarbazone with nickel acetate tetrahydrate and pyridine yielded the title compound, [Ni(C8H6BrN3OS)(C5H5N)]. The NiII atom is four-coordinated in a square-planar environment by one deprotonated dianionic thiosemicarbazone ligand, acting in a tridentate chelating mode through N, O and S atoms forming two metalla-rings, and by one pyridine molecule. The complex molecules are linked into dimers by pairs of centrosymmetrical N—H⋯N interactions. In addition, molecules are connected through intermolecular Br⋯Br interactions [3.545 (1) Å], forming chains along the b-axis direction.

The reaction of 5-bromosalicylaldehyde thiosemicarbazone with nickel acetate tetrahydrate and pyridine yielded the title compound, [Ni(C 8 H 6 BrN 3 OS)(C 5 H 5 N)]. The Ni II atom is four-coordinated in a square-planar environment by one deprotonated dianionic thiosemicarbazone ligand, acting in a tridentate chelating mode through N, O and S atoms forming two metalla-rings, and by one pyridine molecule. The complex molecules are linked into dimers by pairs of centrosymmetrical N-HÁ Á ÁN interactions. In addition, molecules are connected through intermolecular BrÁ Á ÁBr interactions [3.545 (1) Å ], forming chains along the b-axis direction.
Symmetry code: (i) Àx þ 2; Ày À 1; Àz.   (Joseph et al., 2010). As part of our study of thiosemicarbazone derivatives, we report herein the synthesis and the crystal structure of a new Ni II complex with 5-bromosalicylaldehyde thiosemicarbazone. In the title compound, in which the molecular structure unit matches the asymmetric unit, the Ni II ion is coordinated in a square planar environment by one deprotonated dianionic 5bromosalicylaldehyde thiosemicarbazone and one pyridine ligand (Fig. 1). The selected bond angles formed between donor atoms trough the Ni atom are N1-Ni1-N4 = 177.00 (10)° and O1-Ni1-S1 = 176.46 (6)°, and show a slightly distorted coordination environment. The thiosemicarbazone ligand is coordinated to the Ni II ion in a tridentate chelating mode, forming five-and six-membered rings, as a "NOS" donor with the O/S atoms trans to each other, while the N1 azomethine atom is trans to the N4 atom from the pyridine ligand.
The acidic hydrogen of the hydrazine fragment is lost by the reaction with KOH, which is in agreement with thiosemicarbazone derivatives prepared from aldehydes or ketones. The negative charge is delocalized over the C-N-N-C-S fragment as indicated by their intermediate bond distances. The imine and thioamide C-N distances indicate considerable double bond character, while the C-S distance is consistent with increased single bond character. These distances are C7-N1 = 1.295 (3) Å, N1-N2 = 1.403 (3) Å, N2-C8 = 1.289 (4) Å and C8-S1 = 1.735 (3) Å. The hydrogen of the hydroxyl group is also deprotonated with KOH, resulting in the dianionic form of the ligand.
The crystal structure shows that molecules are additionally connected through intermolecular Br···Br interactions into chains along the crystallographic b direction (Fig. 3). The Br···Br distances amount to 3.545 (1) Å, which are shorter than the sum of the van der Waals radii for Br atoms (3.70 Å).

Experimental
Starting materials were commercially available and were used without further purification. The synthesis of 5-bromosalicylaldehyde thiosemicarbazone was adapted from a procedure reported previously (Joseph et al., 2010). 5-Bromosalicylaldehyde thiosemicarbazone (0.5 mmol) was dissolved in tetrahydrofurane (50 ml) and treated with one KOH pellet. After 30 min stirring under slight warming to 333 K, the solution was filtered and added to a nickel acetate tetrahydrate (0.5 mmol) solution in pyridine (10 ml). The reaction mixture was refluxed for 4 h under continuous stirring and showed a brown-red colour. Brown-red crystals of the complex, suitable for X-ray analysis, were obtained after six weeks by adding a 3:1 mixture of dimethylformamide and toluene (80 ml) to the reaction solution.

Refinement
H atoms attached to C atoms were positioned with idealized geometry and were refined isotropic with U eq (H) set to 1.2 times of the U eq (C) using a riding model with C-H = 0.93 Å. H atoms attached to N atoms atoms were positioned with idealized geometry and were refined isotropically with U eq (H) set to 1.2 times of U eq (N) using a riding model with N3-H1 = 0.7822 Å and N3-H2 = 0.8025 Å.      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 R-factors(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.