Supramolecular architectures in cytosinium 6-chloronicotinate monohydrate and 5-bromo-6-methylisocytosinium hydrogen sulfate.

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 primary R22(8) ring motif (supramolecular heterosynthon) is formed via a 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, forming R22(8), R32(7) and R55(21) motifs, leading to a hydrogen-bonded supramolecular sheet structure. The supramolecular double sheet structure is formed via water-carboxylate O-H...O hydrogen bonds and π-π interactions between the anions and the cations. In salt (II), the hydrogen sulfate ions are linked via O-H...O hydrogen bonds to generate zigzag chains. The aminopyrimidinium cations are embedded between these zigzag chains. Each hydrogen sulfate ion bridges two cations via pairs of N-H...O hydrogen bonds and vice versa, generating two R22(8) ring motifs (supramolecular heterosynthon). The cations also interact with one another via halogen-halogen (Br...Br) and halogen-oxygen (Br...O) interactions.