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In the crystal structure of the title compound, C6H10N3+·Br−·C6H9N3·H2O, the asymmetric unit contains a 2-amino-4,6-di­methyl­pyrimidinium cation, a Br− anion, a neutral 2-amino-4,6-di­methyl­pyrimidine mol­ecule and a water mol­ecule. Each neutral base molecule is paired with another inversion-related molecule through N—H⋯N hydrogen bonds to form dimers, and these are linked to one another through water-mediated hydrogen bonds, generating a supramolecular ribbon. The cations also pair with one another through N—H⋯N hydrogen bonds. The cation pairs are stacked on top of the neutral pairs. The Br− anion also takes part in hydrogen bonding (N/O—H⋯Br). [ABSTRACT FROM AUTHOR]

In the title compounds, namely 2,4-diamino-5-[(3,4,5-trimethoxy­phenyl)methyl]­pyrimidin-1-ium pyridine-2-carboxyl­ate, C14H19N4O3+·C6H4NO2−, (I), and 2-amino-4,6-dimethyl­pyrimidin-1-ium pyridine-2-carboxyl­ate hemihydrate, C6H10N3+·C6H4NO2−·0.5H2O, (II), the trimethoprim and 2-amino-4,6-dimethyl­pyrimidin-1-ium cations are protonated at one of the pyrimidine N atoms. In (I), bifurcated hydrogen bonds are observed between a picolinate O atom, the protonated N atom and the 2-amino group; the graph-set designator is R21(6). The pyrimidine moieties of the trimethoprim cations are centrosymmetrically paired through a pair of N—H⋯N hydrogen bonds. In addition to the base pairing, one of the picolinate O atoms bridges the 2- and 4-amino groups on either side of the paired bases, resulting in a complementary DADA array. In (II), the carboxyl­ate group of the picolinate anion binds with the protonated pyrimidine N atom and the 2-amino group of the pyrimidine moiety through a pair of N—H⋯O hydrogen bonds, leading to the common ring motif R22(8). The water mol­ecule, which resides on a twofold rotation axis, bridges the carboxyl­ate group of the picolinate anion via O—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]