Experimental

R factor = 0.047; wR factor = 0.131; data-to-parameter ratio = 21.0. In the 4-methoxyquinoline-2-carboxylate anion of the title salt, C5H8N3 +C11H8NO3, the dihedral angle between the quinoline ring system and the carboxylate group is 16.54 (15). In the crystal, the cations and anions are linked via N—H O and N—H N hydrogen bonds, forming a centrosymmetric 2 + 2 aggregate with R2 2(9) and R4 2(8) ring motifs. These units are further connected via N—H O hydrogen bonds into a layer parallel to the bc plane. The crystal structure is also stabilized by weak C—H O hydrogen bonds and – interactions between pyridine rings [centroid–centroid distance = 3.5886 (8) Å] and between pyridine and benzene rings [centroid–centroid distance = 3.6328 (8) Å]. Related literature For background to the chemistry of substituted pyridines, see: Pozharski et al. (1997); Katritzky et al. (1996). For background to and the biological activity of quinoline derivatives, see: Morimoto et al. (1991); Markees et al. (1970). For a related structure, see: Hemamalini & Fun (2011). For hydrogen-bond motifs, see: Bernstein et al. (1995). For bond-length data, see: Allen et al. (1987). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986)