In crystals of the title compound, 2-aminopyrimidin-1-ium hemifumarate hemi
fumaric acid, C4H6N3+. 0.5C(4)H(2)O(4)(2-). 05C(4)H(4)O(4), the asymmetric
unit contains one 2-aminopyrimidine cation, C4H6N3+, protonated at a pyrimi
dine ring-N atom, one half-molecule of fumaric acid, C4H4O4, and one half o
f a fumarate ion, C4H2O42-. These are linked by N-H ... O, O-H ... O and re
latively strong C-H ... O bonds, resulting in eight- and nine-membered hydr
ogen-bonded rings and an extended supramolecular structure.