Hydrogen-bonding patterns in pyrimethaminium pyridine-3-sulfonate

Abstract

In the asymmetric unit of the title salt [systematic name: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium pyridine-3-sulfonate], C12H14N4Cl+·C5H4NSO3−, there are two independent pyrimethaminium cations and two 3-pyridine sulfonate anions. Each sulfonate group interacts with the corresponding protonated pyrimidine ring through two N—H...O hydrogen bonds, forming a cyclic hydrogen-bonded bimolecular R22(8) motif. Even though the primary mode of association is the same, the next higher level of supramolecular architectures are different due to different hydrogen-bonded networks. In one of the independent molecules in the asymmetric unit, the pyrimethamine cation is paired centrosymmetrically through N—H...N hydrogen bonds, generating an R22(8) ring motif. In the other molecule, the pyrimethamine cation does not form any base pairs; instead it forms hydrogen bonds with the 3-pyridine sulfonate anion. The structure is further stabilized by C—H...O, C—H...N and π–π stacking [centroid–centroid distance = 3.9465 (13) Å] interactions.