In the crystal structures of the two organic salts, namely, pyrimethamine hydrogen glutarate (1:1) 1 and pyrimethamine formate (1:1) 2, the pyrimethamine moieties are protonated at one of the nitrogen atoms of the pyrimidine rings. The carboxylate group of the respective anions (hydrogen glutarate and formate) interacts with the protonated pyrimidine moiety in a near linear fashion through a pair of N−H···O hydrogen bonds. The dihedral angle between the diaminopyrimidine and the p-chlorophenyl plane is 74.8(1)° in compound 1, and the corresponding value in compound 2 is 76.7(1)°. In both compounds, the pyrimidine moieties are centrosymmetrically paired through a pair of N−H···N hydrogen bonds. The 2-amino group of the one member of the pair and the 4-amino group of the other member are bridged by an O atom of the carboxylate group, using a pair of N−H···O hydrogen bonds. This combination of hydrogen bonds results in the complementary DADA (D = donor and A = acceptor in hydrogen bonds) arrays of quadruple hydrogen-bonding patterns. In compound 1, there are chains and ladders made up of the O−H···O, N−H···O, and C−H···N hydrogen bonds whereas compound 2 displays a three-dimensional network of hydrogen bonds.

Key indicatorsSingle-crystal X-ray study T = 293 K Mean '(C±C) = 0.004 A Ê R factor = 0.054 wR factor = 0.142 Data-to-parameter ratio = 11.8For details of how these key indicators were automatically derived from the article, see

Pyrimethamine [2,4-diamino-5-(p-chlorophenyl)-6-ethyl-pyrimidine] (PMN) is an antifolate drug. Four new organic salts, namely, PMN hydrogen maleate (1), PMN hydrogen succinate (2), PMN hydrogen phthalate (3), and PMN fumarate (4), have been synthesized and their hydrogen bonding patterns have been analyzed. As expected, in all the structures, the PMN moieties are protonated at one of the nitrogen atoms of the pyrimidine rings. The carboxylate group of the respective anions interacts with the protonated pyrimidine moiety in near linear fashion through a pair of N-H‚‚‚O hydrogen bonds to form a cyclic hydrogen-bonded motif. The crystal structures of compounds 1 and 2 are isomorphous as revealed by the very good agreement among their cell parameters. Interestingly, the hydrogen succinate mimics the hydrogen maleate here. In all three crystal structures (1-3), the hydrogen bonding motifs and their supramolecular patterns are the same, which is significant from a crystal engineering point of view in the building up of organic ionic ladders. In compound 4, the cyclic hydrogen-bonded motifs are self-organized through N-H‚‚‚O, N-H‚‚‚Cl, and C-H‚‚‚N hydrogen bonds to the formation of different types of hydrogen bonding patterns.