In this thesis, I will address the solid state chemistry of certain derivatives of the pharmaceutically active compounds sulfadiazine and sulfapyridine, and specifically analyze the intermolecular interactions and packing modes. Supramolecular synthons can be drawn from the structural features. In crystals of the neutral sulfadiazine and N-(6-methyl-2-pyridyl)mesitylene-sulfonamide (MPMS), dimers always form. In crystals of the protonated sulfonamide, however, the situation is different: In the case of protonated sulfadiazine, the protonation always occurs at the aniline NH2 group. Consequently, the anions are more inclined to form hydrogen bond with this NH2 group because of its higher acidity, and this makes the formation of dimers still possible although the proton moves from amide-N to pyrimidine-N. Pronation occurs at the only remaining N atom in the MPMS cation, therefore two N-H groups separated by one carbon atom clamp the counter anion by way of hydrogen bonds. In addition to these neighbouring hydrogen bonds, aromatic interactions such as pi - or T - stacking among rings rely more on the space filling effect.