The quinoline rings with atoms O(1), C(11), O(3), and C(13) in both molecules lie in a single plane to within 0.02 Å despite the presence of shortened intramolecular contacts H(2)···C(11) 2.67 in A and 2.65 Å in B (sum of van der Waals radii 2.87 Å [6]). The bond lengths N(1)–C(9) 1.33(1) in A, 1.34(1) in B and O(1)–C(9) 1.34(1) in A and 1.33(1) Å in B are somewhat shortened when compared with the mean values of 1.355 and 1.370 Å [7], as a result of which the structure of the organic cation can be represented as a resonance hybrid of the two canonical structures 4 and 4a.