The title co-crystal, C9H9NO2·C6H6O2, is composed of one 2,6-diacetyl­pyridine mol­ecule and one resorcinol mol­ecule as the asymmetric unit. In the 2,6-diacetyl­pyridine mol­ecule, the two carbonyl groups are anti­periplanar to the pyridine N atom. In the crystal, the 2,6-diacetyl­pyridine and resorcinol mol­ecules are connected by two O—H⋯O hydrogen bonds, forming planar chains of alternating components running along [120].

Chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) and 2,6-diaminopyridine react to form the title salt, C5H8N3+·C7H4NO5−; there are two formula units in the asymmetric unit. The pyridine N atom of 2,6-diaminopyridine is protonated whereas chelidamic acid is deprotonated at both carboxylate groups but protonated at the N atom; the reaction involves intra- and intermolecular proton transfer. In the crystal, each 2,6-diaminopyridinium cation participates in five strong N—H...O hydrogen bonds (including one bifurcated hydrogen bond). The crystal structure also features strong O—H...O hydrogen bonds between the chelidamate anions, leading to chains along the a axis

The title compound, C15H25N5, is an aminalization product between 2,6-diacetyl­pyridine and 1,3-diamino­propane. It crystallizes with two independent mol­ecules in the asymmetric unit with different conformations. In the first mol­ecule, the methyl groups are cis oriented with respect to the pyridine ring [N—C—C—C torsion angles = 72.5 (1) and 80.3 (1)°], while they are trans oriented in the second mol­ecule [N—C—C—C torsion angles = 82.6 (1) and −90.8 (1)°]. Each of the two mol­ecules forms centrosymmetric dimers held together by N—H⋯N hydrogen bonds, thus forming R 2 2(16) rings. The two dimers are inter­linked by additional N—H⋯N bonds into R 4 4(14) rings, building chains along the a axis. These patterns influence the orientation (either equatorial or axial) of the N—H bonds.