2-Amino-5-chloro-pyridinium (Z)-3-carb-oxy-prop-2-enoate 0.25-hydrate

In the title hydrated salt, C(5)H(6)ClN(2) (+)·C(4)H(3)O(4) (-)·0.25H(2)O, the water O atom lies on a twofold axis with 0.25 occupancy. The 2-amino-5-chloro-pyridinium cation is almost planar, with a maximum deviation of 0.015 (3) Å. In the hydrogen malate anion, an intra-molecular O-H⋯O hydrogen bond generates an S(7) ring and results in a folded conformation. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) ring motif. The ion pairs are further connected via O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, forming layers parallel to the ab plane which stack down the c axis.