Trimethoprim-hydrogen malonate (1/1)

In the title compound, 2,4-diamino-5-(3,4,5-trimethoxybenzyl) pyrimidinium hydrogen malonate, C14H19N4O3+.C3H3O4-, the trimethoprim molecule is protonated at one of the pyrimidine N atoms. The carboxylate group of the hydrogen malonate ion accepts a pair of N - H ... O hydrogen bonds from an adjacent trimethoprim molecule, which is similar to the carboxylate - trimethoprim cation interaction present in the complex of dihydrofolate reductase with trimethoprim. An O atom of the carboxyl group forms an intramolecular O - H ... O hydrogen bond with the carboxylate group, leading to a folded conformation for the hydrogen malonate ion. Each hydrogen malonate ion bridges two diaminopyrimidine cations, via N - H ... O and C - H ... N hydrogen bonds, leading to a supramolecular ribbon made up of alternating cations and anions. Two such inversion-related ribbons are cross-linked by ( amino) N - H ... O( methoxy) hydrogen bonds, ( pyrimidine) C - H ... O( methoxy) hydrogen bonds and pi-pi stacking involving the benzene planes.