6-(2-Methylphenyl)-3-(3,4,5-trimethoxyphenyl)-1,2,4-triazolo[3,4-b][1,3,4]thiadiazole

In the molecule of the title compound, C19H18N4O3S, the planar central heterocylic ring system is oriented with respect to the trimethoxyphenyl and 2-methylphenyl rings at dihedral angles of 4.43 (3) and 4.32 (3)°, respectively. The dihedral angle between the two benzene rings is 7.65 (4)°. In the crystal structure, intermolecular C—H⋯N hydrogen bonds link the molecules into centrosymmetric R 2 2(18) dimers. These dimers are connected via a C—H⋯π contact between the 2-methylphenyl and trimethoxyphenyl rings, and a π–π contact between the thiadiazole and trimethoxyphenyl rings [interplanar distance 3.51 Å, dihedral angles 4.17(4)°]. An intramolecular C—H⋯N hydrogen bond is also present.

In the molecule of the title compound, C 19 H 18 N 4 O 3 S, the planar central heterocylic ring system is oriented with respect to the trimethoxyphenyl and 2-methylphenyl rings at dihedral angles of 4.43 (3) and 4.32 (3) , respectively. The dihedral angle between the two benzene rings is 7.65 (4) . In the crystal structure, intermolecular C-HÁ Á ÁN hydrogen bonds link the molecules into centrosymmetric R 2 2 (18) dimers. These dimers are connected via a C-HÁ Á Á contact between the 2methylphenyl and trimethoxyphenyl rings, and acontact between the thiadiazole and trimethoxyphenyl rings [interplanar distance 3.51 Å , dihedral angles 4.17 (4) ]. An intramolecular C-HÁ Á ÁN hydrogen bond is also present.
In the molecule of the title compound ( In the crystal structure, intermolecular weak C-H···N hydrogen bonds (Table 1) link the molecules to form a R 2 2 (18) ring motif ( Fig. 2) (Bernstein et al., 1995), in which they may be effective in the stabilization of the structure. The C-H···π contact (Table 1) between the 2-methylphenyl and trimethoxyphenyl rings and a π-π contact between the thiadiazole and trimethoxyphenyl rings CgC···CgA i [symmetry code: (i) 1 -x, 1 -y, 1 -z] further stabilize the structure, with centroid-centroid distance of 3.506 (1) Å.

S2. Experimental
For the preparation of the title compound, 4-amino-5-(3,4,5-trimethoxyphenyl) -4H-1,2,4-triazole-3-thiol (0.01 M) and 2methylbenzoic acid (0.01 M) were dissolved in dry phosphorous oxychloride (10 ml). The resulted solution was further heated under reflux for 7 h. The reaction mixture was cooled to room temperature and the mixture was gradually poured onto crushed ice with stirring. Finally, powdered potassium carbonate and the required amount of solid potassium hydroxide were added until the pH of the mixture was raised to 8, to remove the excess of phosphorous oxychloride. The mixture was allowed to stand overnight and the solid was separated. It was filtered, washed with cold water, and then dried. Crystals suitable for X-ray analysis were obtained by the recrystallization of the solid residue from a mixture of N,N-dimethyl-formamide/ethanol (1:1) by slow evaporation at room temperature.

S3. Refinement
H atoms were positioned geometrically, with C-H = 0.95 and 0.98 Å for aromatic and methyl H, respectively, and constrained to ride on their parent atoms with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for aromatic H supporting information atoms.

Figure 1
The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.  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 > 2sigma(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.