10-Benzyl-4-oxo-2,3,4,10-tetrahydropyrimido[4,5-b]quinolin-2-iminium chloride sesquihydrate: a polarized electronic structure within a complex hydrogen-bonded sheet structure.

In the title compound, C(18)H(15)N(4)O(+).Cl(-).1.5H(2)O, one water site is fully ordered with unit occupancy while the other, which lies close to an inversion centre in the space group C2/c, has only 0.5 occupancy. The cation exhibits bond fixation in the fused carbocyclic ring and electronic polarization in the terminal heterocyclic ring. The components are linked into complex sheets by a combination of N-H...O, N-H...Cl, O-H...O, O-H...Cl and C-H...O hydrogen bonds.