Melaminium maleate monohydrate.

In the title compound, 2,4,6-triamino-1,3,5-triazin-1-ium maleate monohydrate, C3H7N6+.C4H3O4-.H2O, containing singly protonated melaminium residues, maleate(1-) anions and water molecules, the components are linked by hydrogen bonds into a three-dimensional framework structure. The melaminium residues are connected by two pairs of N-H...N hydrogen bonds into chains in the form of stacks, with a distance of 3.26 (1) A between the triazine rings, clearly indicating pi-pi interactions. The maleate anion contains an intramolecular O-H...O hydrogen bond and the anions interact with the water molecules via O-H...O hydrogen bonds, forming zigzag chains, also in the form of stacks, in which the almost-planar maleate anions are separated by 3.26 (1) A. The experimental geometries of the ions are compared with molecular-orbital calculations of their gas-phase geometries.