Pyridazine-3,6-di­carboxyl­ic acid monohydrate

The title compound, C4H4N2O4·H2O, is a triclinic polymorphic form of pyridazine-3,6-di­carboxyl­ic acid monohydrate. The dihedral angles between the planes of the carboxyl­ic acid groups and the planar pyrazine ring are 2.0 (2) and 5.6 (2)°. The acid and water mol­ecules form almost planar sheets connected by hydrogen bonds, with O⋯O distances ranging from 2.5143 (14) to 2.7330 (16) A and an O⋯N distance of 2.8234 (18) A. The shortest distance between two adjacent sheets is 3.2 (1) A, indicating van der Waals-type interactions.