Ammonium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate monohydrate.

Each anion of the title salt, NH4+.C8HN4O2-.H2O, is linked by two N-H...O hydrogen bonds to another anion, thus forming an essentially planar centrosymmetric dimer. The dimers are considered to be molecular building blocks of an anionic wall. The building blocks form infinite ribbons via -C-N...N-C- dipole-dipole and pi-pi interactions. Adjacent ribbons are stacked by means of pi-pi interactions, thus forming an anionic wall. Neighbouring walls are connected by (NH4+...H2O)n chains running along the b axis.