4-[(5-Chloro-2-hydroxybenzylidene)amino]-3-ethyl-1H-1,2,4-triazole-5(4H)-thione

The title compound, C11H11ClN4OS, crystallizes with two molecules, A and B, in the asymmetric unit in which the dihedral angles between the triazole and benzene rings are 54.6 (3) and 56.0 (3)°. Both molecules feature an intramolecular O—H⋯N hydrogen bond, which generates an S(6) ring. In the crystal, A–B dimers are linked by pairs of weak C—H⋯S hydrogen bonds along with π–π stacking interactions between the triazole rings [centroid–centroid separations = 3.631 (3) and 3.981 (4)Å]. N—H⋯S hydrogen bonds link the dimers into [100] chains, which feature R 2 2(8) loops.

The title compound, C 11 H 11 ClN 4 OS, crystallizes with two molecules, A and B, in the asymmetric unit in which the dihedral angles between the triazole and benzene rings are 54.6 (3) and 56.0 (3) . Both molecules feature an intramolecular O-HÁ Á ÁN hydrogen bond, which generates an S(6) ring. In the crystal, A-B dimers are linked by pairs of weak C-HÁ Á ÁS hydrogen bonds along withstacking interactions between the triazole rings [centroid-centroid separations = 3.631 (3) and 3.981 (4)Å ]. N-HÁ Á ÁS hydrogen bonds link the dimers into [100] chains, which feature R 2 2 (8) loops.

Comment
The incorporation of the 1,2,4-triazole unit into Schiff base is of considerable current interest as complexes of 1,2,4triazoles which are being developed for potential use in pharmaceutical and material applications (Sumangala et al. 2013;Brandt et al. 2007). Therefore, the title compound (I), has been synthesized and its crystal structure has been determinated.
The crystal structure is illustrated in Fig. 1 and the main geometric parameters of the commpound are listed in Table 1.
The title compound (I) crystallizes in the monoclinic space group P2 1 with two symmetry-independent molecules in the unit cell. The bond lengths of N4-C5 (1.275 Å) and N8-C16 (1.272 Å) confirm them as double bonds, which is similar to those reported in other Schiff bases (Pannu et al. 2011;Wu et al. 2012;). It is noticeable that the C-S bond length (1.670 Å) in the compound is close to C═S double bond, indicating that the compound exists in the thione form.
The packing arrangement in the crystal structure of (I) is shown in Fig. 2. As is a common feature of o-hydroxysalicylidene systems, the compound displays the strong intermolecular and intramolecular hydrogen bond between atoms N, O and S. The molecules of the compound is linked by an inversion-related pair of almost linear intermolecular hydrogen bonds N-H···S to form the cyclic centrosymmetric dimers characterized by an R 2 2 (8) motif. The dimer is further held together by the π-π interactions between two rings (Cg1 and Cg2) in the crystal.

Refinement
The H atoms bonded to C atoms were placed in calculated positions (C-H=0.96, 0.97 and 0.93 Å for Csp 3 , Csp 2 and Csp atoms, respectively), assigned fixed U iso values [U iso H)=1.2 U eq (Csp 2 ) and 1.5U eq (Csp 3 )] and treated as riding atoms. The H atoms attached to O and N atoms were found in the difference electron-density map and were refined isotropically,  The view of the structure of (I) with displacement ellipsoids drawn at the 30% probability level. Dotted lines indicate hydrogen bonds and π-π interactions.  A part of the crystal structure I showing formation of a chain of R 2 2 (8) hydrogen-bonded rings and π-π stacking between Cg1 and Cg2 rings; Cg1: C1/C2/N1/N2/N3, Cg2: C12/C13/N5/N6/N7, Symmetry codes: i) x, y, z+1; ii) x, y, z-1. 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.