Melaminium bis(4-hydroxybenzenesulfonate) dihydrate.

The crystals of a new melaminium salt, 2,4,6-triamino-1,3,5-triazine-1,3-diium bis(4-hydroxybenzenesulfonate) dihydrate, C3H8N6(2+)*2C6H5O4S-*2H2O, are built up from doubly protonated melaminium(2+) residues, dissociated p-phenolsulfonate anions and water molecules. The doubly protonated melaminium dication lies on a twofold axis. The hydroxyl group of the p-hydroxybenzenesulfonate residue is roughly coplanar with the phenyl ring [dihedral angle 13 (2) degrees ]. A combination of ionic and donor-acceptor hydrogen-bond interactions link the melaminium and p-hydroxybenzenesulfonate residues and the water molecules to form a three-dimensional network.