Bis­(2-amino-5-methyl­pyridinium) fumarate–fumaric acid (1/1)

In the crystal structure of the title compound, C(6)H(9)N(2) (+)·0.5C(4)H(2)O(4) (2−)·0.5C(4)H(6)O(4), the fumarate dianion and fumaric acid mol­ecule are located on inversion centres. The 2-amino-5-methyl­pyrimidinium cation inter­acts with the carboxyl­ate group of the fumarate anion through a pair of N—H⋯O hydrogen bonds, forming an R (2) (2)(8) ring motif. These motifs are centrosymmetrically paired via N—H⋯O hydrogen bonds, forming a complementary DDAA array. The carboxyl groups of the fumaric acid mol­ecules and the carboxyl­ate groups of the fumarate anions are hydrogen bonded through O—H⋯O hydrogen bonds, leading to a supra­molecular chain along [101]. The crystal structure is further stabilized by weak C—H⋯O hydrogen bonds.