Aminopyrimidine derivatives are biologically important as they are components of nucleic acids and drugs. The crystals of two new salts, namely cytosinium 6-chloronicotinate monohydrate, C4H6N3O+·C6H3ClNO2−·H2O, (I), and 5-bromo-6-methylisocytosinium hydrogen sulfate (or 2-amino-5-bromo-4-oxo-6-methylpyrimidinium hydrogen sulfate), C5H7BrN3O+·HSO4−, (II), have been prepared and characterized by single-crystal X-ray diffraction. The pyrimidine ring of both compounds is protonated at the imine N atom. In hydrated salt (I), the primaryR22(8) ring motif (supramolecular heterosynthon) is formedviaa pair of N—H...O(carboxylate) hydrogen bonds. The cations, anions and water molecule are hydrogen bonded through N—H...O, N—H...N, O—H...O and C—H...O hydrogen bonds, formingR22(8),R32(7) andR55(21) motifs, leading to a hydrogen-bonded supramolecular sheet structure. The supramolecular double sheet structure is formedviawater–carboxylate O—H...O hydrogen bonds and π–π interactions between the anions and the cations. In salt (II), the hydrogen sulfate ions are linkedviaO—H...O hydrogen bonds to generate zigzag chains. The aminopyrimidinium cations are embedded between these zigzag chains. Each hydrogen sulfate ion bridges two cationsviapairs of N—H...O hydrogen bonds andvice versa, generating twoR22(8) ring motifs (supramolecular heterosynthon). The cations also interact with one anotherviahalogen–halogen (Br...Br) and halogen–oxygen (Br...O) interactions.
