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Three salts, namely 2-amino-4,6-dimethylpyrimidin-1-ium thiobarbiturate trihydrate (I), 2-amino-4,6-dimethoxypyrimidin-1-ium thiobarbiturate dihydrate (II) and 2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidin-1-ium thiobarbiturate (III), were synthesized and characterized by IR and X-ray diffraction techniques. The primary interaction between the acid and base happens via N-H...O hydrogen bonds in (II) and (III), and via water-mediated N-H...O W and O W-H W...S in (I). The water molecules present in compound (I) form a (H2O)12 water cluster via water-water interactions. In all three compounds (I)-(III), thiobarbiturate anions form self-complementary pairs with a robust R22(8) motif via a pair of N-H...O/N-H...S hydrogen bonds. They mimic the nucleobase base pairs by utilizing the same groups (thymine/uracil uses N3-H and C4=O8 groups during the formation of Watson-Crick and Hoogsteen base pairs with adenine). Compound (I) forms a water-mediated base pair through N-H...O W hydrogen bonds and forms an R42(12) motif. The formation of N-H...S hydrogen bonds, water-mediated base pairs and water-water interactions in these crystal systems offers scope for these systems to be considered as a model in the study of hydration of nucleobases and water-mediated nucleobase base pairs in macromolecules. [ABSTRACT FROM AUTHOR]

In the crystal structure of the title compound, 2C6H9N3 C8H6O4, terephthalic acid has a crystallographic inversion centre and the dimethylpyrimidine molecule shows approximate non-crystallographic mirror and twofold rotation symmetry. The inversion-related pyrimidine molecules form a base pair [R2 2(8) ring motif] via a pair of NH⋯N hydrogen bonds. The carboxyl groups of terephthalic acid link the base pairs via OH⋯N and NH⋯O hydrogen bonds [R2 2(8) motif] to generate a supramolecular ribbon. [ABSTRACT FROM AUTHOR]

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 π–π stacking involving the benzene planes. [ABSTRACT FROM AUTHOR]

In the title compound, C12H14ClN4+·C6H4NO2−·H2O, the pyrimethamine molecule is protonated at one of the pyrimidine N atoms. The protonated N atom and 2-amino group of the cation interact with an adjacent nicotinate anion through a pair of N—H...O hydrogen bonds [graph set R22(8)]. The cation, anion and water molecule form a hydrogen-bonded ring motif with graph-set notation R42(8). The crystal structure is further stabilized by N—H...O and O—H...O hydrogen bonds and π–π interactions [centroid–centroid distance = 3.637 (6) Å]. [ABSTRACT FROM AUTHOR]

Polymorphs of 2-amino-4,6-dimethoxypyrimidine [ADMP (1)], 2,4-diamino-6-methyl-1,3,5-triazine [DAMT ( 2 )], 2,4-diamino-6-phenyl-1,3,5-triazine [DAPT ( 3 )] and a solvate of DAPT with DMF solvent, [DAPT·DMF ( 4 )] were obtained either during a systematic screening using various solvents or by serendipity. These polymorphs and solvates were then characterized using single crystal X-ray diffraction technique and their structural and supramolecular aspects are analyzed. The supramolecular architecture of compounds ( 1 – 4 ) are predominantly hydrogen bonded via N–H⋯N base pairs. These base pairs are formed either between crystallographically independent molecules in the lattice or between symmetry related molecules. The molecular self assembly process involved in 2 , 3 and 4 , facilitates the formation of some base pair motifs with graph-set of R 2 2 (8) and a rare non-complementary base pair motif with graph-set R 2 2 (10). The other interesting supramolecular patterns and non-covalent interactions which lead to the formation of new forms are discussed in detail. [ABSTRACT FROM AUTHOR]