Molecular cocrystals of 5-(4-bromophenyl)-1,3,4-thiadiazol-2-amine: hydrogen bonding in the structures of the 1:1 adduct with 2-(naphthalen-2-yloxy)acetic acid and the salt with 3,5-dinitrobenzoic acid.

The crystal structures of the anhydrous products from the interaction of 5-(4-bromophenyl)-1,3,4-thiadiazol-2-amine with 2-(naphthalen-2-yloxy)acetic acid, viz. the 1:1 adduct C8H6BrN3S·C12H10O3, (I), and with 3,5-dinitrobenzoic acid, viz. the salt 2-amino-5-(4-bromophenyl)-1,2,4-thiadiazol-3-ium 3,5-dinitrobenzoate, C8H7BrN3S(+)·C7H3N2O6(-), (II), have been determined. In adduct (I), a heterodimer is formed through a cyclic hydrogen-bonding motif [graph set R2(2)(8)], involving carboxylic acid-heteroatom O-H···N and amine-carboxylic acid N-H···O interactions. The heterodimers are essentially planar, with a thiadiazole-to-naphthalene ring dihedral angle of 15.9 (2)° and an intramolecular thiadiazole-to-benzene ring angle of 4.7 (2)°. An amine-heteroatom N-H···N hydrogen bond between the heterodimers generates a one-dimensional chain structure extending down [001]. Also present are weak benzene-benzene and naphthalene-naphthalene π-π stacking interactions down the b axis [minimum ring-centroid separation = 3.936 (3) Å]. With salt (II), the cation-anion association is also through a cyclic R2(2)(8) motif but involving duplex N-H···O(carboxylate) hydrogen bonds, giving a heterodimer that is close to planar [dihedral angles between the thiadiazole ring and the two benzene rings = 5.00 (16) (intra) and 7.23 (15)° (inter)]. A secondary centrosymmetric cyclic RR4(2)(8) N-H···O(carboxylate) hydrogen-bonding association involving the second amino H atom generates a heterotetramer. Also present in the crystal structure are weak π-π interactions between thiadiazolium rings [minimum ring-centroid separation = 3.9466 (18) Å], as well as a short Br···O(nitro) interaction [3.314 (4) Å]. The two structures reported here now provide a total of three crystallographically characterized examples of cocrystalline products from the interaction of 5-(4-bromophenyl)-1,3,4-thiadiazol-2-amine with carboxylic acids, of which only one involves proton transfer.