2-Aminopyrimidine–fumaric acid cocrystal

In crystals of the title compound, 2-aminopyrimidin-1-ium hemifumarate hemifumaric acid, C 4 H 6 N 3 + -0.5C 4 H 2 O 4 2- .0.5C 4 H 4 O 4 , the asymmetric unit contains one 2-aminopyrimidine cation, C 4 H 6 N 3 + , protonated at a pyrimidine ring-N atom, one half-molecule of fumaric acid, C 4 H 4 O 4 , and one half of a fumarate ion, C 4 H 2 O 4 2- . These are linked by N-H...O, O-H...O and relatively strong C-H...O bonds, resulting in eight- and nine-membered hydrogen-bonded rings and an extended supramolecular structure.