10-Ethyl-4-oxo-2,3,4,10-tetrahydropyrimido[4,5-b]quinolin-2-iminium 4-toluenesulfonate: a polarized electronic structure in the cation and a hydrogen-bonded sheet structure.

In the title compound, C(13)H(13)N(4)O(+).C(7)H(7)O(3)S(-), the bond distances within the cation provide evidence for the delocalization of the positive charge in a manner reminiscent of guanidinium cations. Three independent N-H...O hydrogen bonds link the ions into centrosymmetric four-ion aggregates, and these are further linked into sheets by a single C-H...O hydrogen bond. This study shows how a single hydrogen bond can link centrosymmetric entities into a continuous sheet structure.