The asymmetric unit of the title compound, 2C5H8N3 +·2C2HO4 −·H2O, contains two crystallographically independent 2,6-diamino­pyridinium cations, a pair of hydrogen oxalate anions and a water mol­ecule. Both 2,6-diamino­pyridinium cations are planar, with maximum deviations of 0.011 (2) and 0.015 (1) Å, and are protonated at the pyridine N atoms. The hydrogen oxalate anions adopt twisted conformations and the dihedral angles between the planes of their carboxyl groups are 31.01 (11) and 63.48 (11)°. In the crystal, the cations, anions and water mol­ecules are linked via O—H⋯O and N—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title hydrated mol­ecular salt, C7H11N2 +·Cl−·2H2O, the pyridine N atom of the 2-amino-4,6-dimethyl­pyridine mol­ecule is protonated. The cation is essentially planar, with a maximum deviation of 0.006 (2) Å. In the crystal, the components are linked by N—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds, thereby forming sheets lying parallel to (100). The crystal structure is further stabilized by aromatic π–π stacking inter­actions between the pyridinium rings [centroid–centroid distance = 3.4789 (9) Å].

In the title molecular salt, C7H16N+·Cl−, the piperidinium ring adopts a chair conformation. In the crystal, the two components are connected by N—H⋯Cl and C—H⋯Cl hydrogen bonds, forming a supra­molecular double-chain structure along the c axis.

In the title compound, C14H16N2O4S2, the dihedral angle between the terminal phenyl rings is 77.07 (13)°. The geometries around the S atoms are distorted tetra­hedral, with O—S—O angles of 120.66 (12) and 119.44 (11)°. In the crystal, mol­ecules are stacked in columns along the a axis via inter­molecular N—H⋯O and C—H⋯O hydrogen bonds.

The complete mol­ecule of the title compound, C27H18F4N2O2, is generated by crystallographic twofold symmetry, with one C atom lying on the rotation axis. The dihedral angle between fluoro-substituted phenyl ring and the adjacent benzene ring is 10.37 (5)°. In the crystal, mol­ecules are connected by N—H⋯O and C—H⋯F hydrogen bonds, resulting in supra­molecular chains propagating along the c direction.