2-[(E)-2-(1H-Indol-3-yl)ethenyl]-1-methylpyridinium 4-chlorobenzenesulfonate

In the title compound, C16H15N2+center dot C6H4ClO3S-, the cation exists in an E configuration with respect to the central C=C bond and is approximately planar, with a dihedral angle of 2.95 (5)degrees between the pyridinium and indole rings. The mean plane of the pi-conjugated system of the cation and the benzene ring of the anion are inclined to each other at a dihedral angle of 69.65 (4)degrees. In the crystal packing, the cations are stacked in an antiparallel manner along the a axis, resulting in a pi-pi interaction with a centroid-centroid distance of 3.5889 (7) angstrom. The anions are linked into a chain along the a axis by weak C-H center dot center dot center dot O interactions. The cations are linked with the anions into a three-dimensional network by N-H center dot center dot center dot O hydrogen bonds and weak C-H center dot center dot center dot O interactions. There are also short O center dot center dot center dot Cl [3.1272 (10) angstrom] and C center dot center dot center dot O [3.1432 (14)-3.3753 (14) angstrom] contacts. The crystal structure is further stabilized by C-H center dot center dot center dot pi interactions.