Bis(2-amino-3-carb-oxy-pyrazin-1-ium) sulfate dihydrate.

The crystal structure of the title compound, 2C(5)H(6)N(3)O(2) (+)·SO(4) (2-)·2H(2)O, displays a variety of N-H⋯O and O-H⋯O hydrogen bonds in which all potential donors and acceptors are involved. In the crystal, cations and anions are inter-connected, forming R(3) (3)(10) and R(2) (2)(8) ring motifs whereas the anions and water mol-ecules form R(2) (3)(10) rings, which develop in chains running along [100]. The resulting three-dimensional network exhibits undulating sheets parallel to (011), marked by the presence of R(6) (6)(26) rings in which six cations are involved.