(E)-1-[(2-Chloro-5-methylpyridin-3-yl)methylene]thiosemicarbazide

The title compound, C8H9ClN4S, which has potential insecticidal activity, was synthesized by the reaction of 2-chloro-5-methylnicotinaldehyde and thiosemicarbazide. In the crystal structure, the molecules are linked via intermolecular N—H⋯N, N—H⋯S and N—H⋯Cl hydrogen bonds, forming a three-dimensional network stacked down a.


Comment
Tyrosinase is a key enzyme in the molting process of insect (Kramer & Knost 2001), and benzaldehyde thiosemicarbazones have inhibitory activity on tyrosinase (Xue et al., 2007). In order to look for highly potent tyrosinase inhibitors, the title compound was synthesized by the reaction of thiosemicarbazide and 2-chloro-5-methylnicotinaldehyde (Liu et al., 2008).
Finally in the preliminary bioassay, we found that it showed obvious inhibitory activity against tyrosinase from cotton bollworm. To get more information about the structure, we prepared a single crystal of the title compound and its crystal will be reported herein.
The bond distances between N2 and C7 is 1.277 (3) Å, which is in the range of typical bond length of imine double bond.
The bond distance of 1.683 (2) Å for the thiocarbonyl group (S1-C8) is about the average value of the typical C=S double bond (1.56 Å) and C-S single bond (1.82 Å), showing a partial double bond character in feature. The partial double bond character also appears between N3 and C8 as well as N4 and C8, which show the distance of 1.355 (3) and 1.322 (3) Å, respectively. In the cryatal structure, there are three intermolecular hydrogen bonds: N3-H3···S1, N4-H4···N1, N4-H4···Cl1 (Table 1). Experimental 1.6 g (10 mmol) 2-Chloro-5-methylnicotinaldehyde was dissolved in anhydrous ethanol (15 ml). To this solution, 0.91 g (10 mmol) thiosemicarbazide and 0.5 mL acetic acid were added. The mixture was refluxed for 24 h and then cooled to room temperatur. The precipitate was formed and collected after filteration. The title compound was obtained in 89% yield after recrystallization of the precipitate from anhydrous MeOH. The colourless crystals suitable for X-ray crystallography was carefully grown from anhydrous methanolic solution.

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.