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The structures of three 3-methyl-1H-1,2,4-triazole-5-thione derivatives are reported. The structure of 4-amino-3-methyl-1H-1,2,4-triazole-5(4H)-thione, C3H6N4S, (I), has been redetermined with an improved model for the H atoms: the non-H atoms of (I) all lie on mirror planes in space group Pbcm, and the H atoms of the methyl group are disordered over two sets of reflection-related atomic sites having occupancy 0.5: two independent N—H...S hydrogen bonds link the molecules of compound (I) into complex sheets. The non-H atoms in the molecules of 4-[(E)-(3,4-dimethoxybenzylidene)amino]-3-methyl-1H-1,2,4-triazol-5(4H)-thione, C12H14N4O2S, (II), despite lying in general positions are close to planar, with a dihedral angle between the two rings of 6.31 (10)°: the molecules of compound (II) are linked by a three-centre N—H...(O)2 hydrogen bond into a C(10)C(11)[R12(5)] chain of rings. A second polymorph of 4-[(E)-(5-bromo-2-hydroxy-5-bromobenzylidene)amino]-3-methyl-1H-1,2,4-triazole-5(4H)-thione, C10H9BrN4OS, (III), has been identified; the non-H atoms are nearly co-planar with a dihedral angle between the two rings of 1.9 (4)°. There is an intramolecular O—H...N hydrogen bond and the molecules are linked by N—H...S hydrogen bonds, forming centrosymmetric R22(8) dimers. Comparisons are made with some related structures.

The title compound, C10H9FN4S, crystallizes with two molecules (A and B) in the asymmetric unit. The dihedral angle between the planes of the trizole and fluorobenzene rings is 7.3 (3)° in molecule A and 41.1 (3)° in molecule B. Molecule A features an intramolecular C—H...S hydrogen bond, which closes an S(6) ring. In the crystal, A+B dimers linked by pairs of N—H...S hydrogen bonds occur, generating R22(8) loops. Weak π–π stacking contacts [centroid–centroid separation = 3.739 (6) Å] are also observed.

In the title compound, C17H16N4OS2, the triazole and methylthiobenzylidene rings are nearly coplanar, making a dihedral angle of 6.52 (12)°. An intramolecular C—H...S hydrogen bond forms an S(6) ring motif. The hydroxybenzyl ring is almost normal to the triazole and methylthiobenzylidene rings, making dihedral angles of 78.56 (12) and 84.79 (11)°, respectively. In the crystal, molecules are linked through O—H...N and N—H...O hydrogen bonds, forming layers parallel to the ac plane. The layers are linked via C—H...N hydrogen bonds, forming a three-dimensional structure. In addition, a short π–π interaction is observed [inter-centroid distance = 3.764 (3) Å], involving inversion-related methylthiobenzylidene rings.