The crystal structure of the title compound, 2C3H5N4O2 +·SO4 2−·2H2O, displays a three-dimensional framework in which mixed infinite chains [oriented parallel to (510) and (10)] inter­fere, forming tunnels extending parallel to the c axis. Inter­molecular O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds ensure the unity of the structure and generate centrosymmetric R 4 4(14) and R 4 2(8) rings. The S atom lies on a twofold axis.

In crystal structure of the title compound, C5H6N3O2 +·NO3 −·H2O, inter­molecular N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds link the cations, anions and water mol­ecules into ribbons extending in [10]. Weak inter­molecular C—H⋯O hydrogen bonds further link these ribbons into sheets parallel to ( 3).

In the title compound, 2C6H7N2O2 +·SO4 2−·3H2O, there are two independent cations which are connected into N—H⋯O hydrogen-bonded dimers. In the crystal, O—H⋯O hydrogen-bonded sulfate–water sheets run parallel to (001) and are linked into a three-dimensional network via inter­molecular N—H⋯O and O—H⋯O hydrogen bonds through the 2-amino­nicotinium dimers. Further stabilization is provided by weak inter­molecular C—H⋯O hydrogen bonds. R 4 3(10) and R 2 2(8) graph-set rings are observed. The crystal studied was an inversion twin with refined components of 0.45 (6) and 0.55 (6).

The crystal structure of the title compound, 2C5H6N3O2 +·SO4 2−·2H2O, 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 inter­connected, forming R 3 3(10) and R 2 2(8) ring motifs whereas the anions and water mol­ecules 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.

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