Bis(melaminium) sulfate dihydrate.

The crystals of a new melaminium salt, bis(2,4,6-triamino-1,3,5-triazin-1-ium) sulfate dihydrate, 2C3H7N6+*SO4(2-)*2H2O, are built up from monoprotonated melaminium(1+) residues, sulfate(2-) anions and water molecules. The SO4(2-) ion has a slightly distorted tetrahedral geometry. The melaminium residues are interconnected by N-H.N hydrogen bonds, forming chains. The chains of melaminium residues develop a three-dimensional network through multiple donor-acceptor hydrogen-bond interactions with sulfate anions and water molecules.