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

The title compound, C11H11BrN4OS, crystallized as a racemic twin with two symmetry-independent molecules in the asymmetric unit. The dihedral angles between the benzene and triazole rings of the two independent molecules are 56.41 (18) and 54.48 (18)°. An intramolecular O—H⋯N hydrogen bond occurs in each molecule. In the crystal, pairs of symmetry-independent molecules are linked by pairs of almost linear N—H⋯S hydrogen bonds, forming cyclic dimers characterized by an R 2 2(8) motif. There are weak π–π interactions between the benzene rings of symmetry-independent molecules, with a centroid–centroid distance of 3.874 (3) Å.

The title compound, C 11 H 11 BrN 4 OS, crystallized as a racemic twin with two symmetry-independent molecules in the asymmetric unit. The dihedral angles between the benzene and triazole rings of the two independent molecules are 56.41 (18) and 54.48 (18) . An intramolecular O-HÁ Á ÁN hydrogen bond occurs in each molecule. In the crystal, pairs of symmetry-independent molecules are linked by pairs of almost linear N-HÁ Á ÁS hydrogen bonds, forming cyclic dimers characterized by an R 2 2 (8) motif. There are weakinteractions between the benzene rings of symmetry-independent molecules, with a centroid-centroid distance of 3.874 (3) Å .   Hydrogen-bond geometry (Å , ).  Recently, 1,2,4-triazoles and their derivatives have been the focus of a great deal of attention owing to their effective biological activities such as antimicrobial, antiviral, analgesic, anti-inflammatory, anticancer and antioxidant properties (Demirbas et al., 2004 and2009;Kochikyan et al., 2011;Kumar et al., 2008;Singhal et al., 2011;Todoulou et al., 1994).

Related literature
As a result, a number of attempts were made to improve the activity of these compounds by varying the substituents on the 1,2,4-triazole nucleus (Popiołek et al., 2013;Sraa et al., 2012). Among these, the amino-and mercapto-group substituted 1,2,4-triazole ring systems represent an important group of compounds that are promising for practical application. Therefore, the title compound (I), has been synthesized and its crystal structure has been determinined.
The crystal structure is illustrated in Fig. 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 [1.274 (5) Å] and N8-C16 [1.272 (5) Å] confirm them as double bonds, which is similar to those reported in other Schiff bases (Pannu et al., 2011;Wu et al., 2012;). The molecule of (I) exists in the thione tautometic form, with C═S distances of 1.673 (4) and 1.672 (4) Å, which indicates a substantial double-bond character (Allen et al., 1987).
The packing arrangement in the crystal structure of (I) is shown in Fig. 2. As a common feature of o-hydroxysalicylidene systems, the azomethine group in title compound forms intramolecular O-H···N hydrogen bonds with the neighbouring hydroxyl groups. Moreover, the crystal structure also contains intermolecular N-H···S hydrogen bonds between both independent molecules with cyclic motifs [graph set R 2 2 (8)] (Bernstein et al., 1995). The molecules are further linked via weak π-π interactions between benzene rings (Cg1 and Cg2). The hydrogen bonds and π-π interactions link the molecules into ribbon structures.

S3. 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) = 1.5 U eq (C) for methyl groups and 1.2 U eq (C) for all others] and treated as riding atoms. The H atoms attached to O and N atoms were found in difference electron-density maps and were refined isotropically, with U iso (H) = 1.5 U eq (O) or U iso (H) = 1.2 U eq (N) and fixed O-H (0.82 Å) and N-H (0.86 Å) bond lengths.

Figure 1
View of the structure with displacement ellipsoids drawn at the 30% probability level. Dotted lines represent hydrogen bonds and π-π interactions.  A part of the crystal structure, showing the formation of a chain of R 2 2 (8) hydrogen-bonded rings and π-π stacking between the benzene rings rings; Cg1: C6/C7/C8/C9/C10/C11, Cg2: C17/C18/C19/C20/C21/C22. Symmetry codes: i) x -1, y. z + 1; ii) x + 1, y, z -1. H atoms without H-bonds have been omitted for clarity.  (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq