Crystal structures of the co-crystalline adduct 5-(4-bromo­phen­yl)-1,3,4-thia­diazol-2-amine–4-nitro­benzoic acid (1/1) and the salt 2-amino-5-(4-bromo­phen­yl)-1,3,4-thia­diazol-3-ium 2-carb­oxy-4,6-di­nitro­phenolate

The structures of the 1:1 co-crystalline adduct C(8)H(6)BrN(3)S·C(7)H(5)NO(4), (I), and the salt C(8)H(7)BrN(3)S(+)·C(7)H(3)N(2)O(7) (−), (II), obtained from the inter­action of 5-(4-bromo­phen­yl)-1,3,4-thia­diazol-2-amine with 4-nitro­benzoic acid and 3,5-di­nitro­salicylic acid, respectively, have been determined. The primary inter-species association in both (I) and (II) is through duplex R (2) (2)(8) (N—H⋯O/O—H⋯O) or (N—H⋯O/N—H⋯O) hydrogen bonds, respectively, giving heterodimers. In (II), these are close to planar [the dihedral angles between the thia­diazole ring and the two phenyl rings are 2.1 (3) (intra) and 9.8 (2)° (inter)], while in (I) these angles are 22.11 (15) and 26.08 (18)°, respectively. In the crystal of (I), the heterodimers are extended into a chain along b through an amine N—H⋯N(thia­diazole) hydrogen bond but in (II), a centrosymmetric cyclic hetero­tetra­mer structure is generated through N—H⋯O hydrogen bonds to phenol and nitro O-atom acceptors and features, together with the primary R (2) (2)(8) inter­action, conjoined R (4) (6)(12), R (2) (1)(6) and S(6) ring motifs. Also present in (I) are π–π inter­actions between thia­diazole rings [minimum ring-centroid separation = 3.4624 (16) Å], as well as short Br⋯O(nitro) inter­actions in both (I) and (II) [3.296 (3) and 3.104 (3) Å, respectively].