5-Amino-6-methyl­quinolin-1-ium hydrogen malonate–malonic acid (2/1)

The asymmetric unit of the title compound, 2C(10)H(11)N(2) (+)·2C(3)H(3)O(4) (−)·C(3)H(4)O(4), consists of one 5-amino-6-methyl­quinolin-1-ium cation, one hydrogen malonate (2-carb­oxy­acetate) anion and one-half mol­ecule of malonic acid which lies on a twofold rotation axis. The quinoline ring system is essentially planar, with a maximum deviation of 0.062 (2) Å for all non-H atoms. In the anion, an intra­molecular O—H⋯O hydrogen bond generates an S(6) ring. In the crystal, the components are linked via N—H⋯O and O—H⋯O hydrogen bonds into layers parallel to the ac plane. The crystal structure also features weak C—H⋯O hydrogen bonds and a π–π stacking inter­action with a centroid–centroid distance of 3.8189 (10) Å.