Proton-transfer compounds with 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide (sulfamethazine): the structures and hydrogen bonding in the salts with 5-nitrosalicylic acid and picric acid

The structures of the anhydrous proton-transfer compounds of the sulfa drug sulfamethazine with 5-nitrosalicylic acid and picric acid, namely 2-(4-aminobenzenesulfonamido)-4,6-dimethylpyrimidinium 2-hydroxy-5-nitrobenzoate, C12H15N4O2S+C7H4NO4, (I), and 2-(4-aminobenzenesulfonamido)-4,6-dimethylpyrimidinium 2,4,6-trinitrophenolate, C12H15N4O2S+C6H2N3O7, (II), respectively, have been determined. In the asymmetric unit of (I), there are two independent but conformationally similar cationanion heterodimer pairs which are formed through duplex intermolecular N+H...Ocarboxylate and NH...Ocarboxylate hydrogen-bond pairs, giving a cyclic motif [graph set R22(8)]. These heterodimers form separate and different non-associated substructures through aniline NH...O hydrogen bonds, one one-dimensional, involving carboxylate O-atom acceptors, the other two-dimensional, involving both carboxylate and hydroxy O-atom acceptors. The overall two-dimensional structure is stabilized by interactions between the pyrimidinium ring and the 5-nitrosalicylate ring in both heterodimers [minimum ring-centroid separation = 3.4580(8)angstrom]. For picrate (II), the cationanion interaction involves a slightly asymmetric chelating NH...O R21(6) hydrogen-bonding association with the phenolate O atom, together with peripheral conjoint R12(6) interactions between the same NH groups and O atoms of the ortho-related nitro groups. An inter-unit amine NH...Osulfone hydrogen bond gives one-dimensional chains which extend along a and inter-associate through interactions between the pyrimidinium rings [centroidcentroid separation = 3.4752(9)angstrom]. The two structures reported here now bring to a total of four the crystallographically characterized examples of proton-transfer salts of sulfamethazine with strong organic acids.