Hydrogen‐bonding patterns in trimethoprim picolinate and 2‐amino‐4,6‐dimethyl­pyrimidinium picolinate hemihydrate

In the title compounds, namely 2,4‐diamino‐5‐[(3,4,5‐trimethoxy­phenyl)methyl]­pyrimidin‐1‐ium pyridine‐2‐carboxyl­ate, C 14 H 19 N 4 O 3 + ·C 6 H 4 NO 2 − , (I), and 2‐amino‐4,6‐dimethyl­pyrimidin‐1‐ium pyridine‐2‐carboxyl­ate hemihydrate, C 6 H 10 N 3 + ·C 6 H 4 NO 2 − ·0.5H 2 O, (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 R 2 1 (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 R 2 2 (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.