Two isomorphous azastilbene derivatives: 1-(2-chlorobenzyl)-4-[(E)-2-(4-hydroxyphenyl)ethenyl]pyridinium chloride and 1-(2-bromobenzyl)-4-[(E)-2-(4-hydroxyphenyl)ethenyl]pyridinium bromide

The crystal structures of the two title (E)-stilbazolium halogenates, C(20)H(17)ClNO+center dot Cl- and C(20)H(17)BrNO+center dot Br-, are isomorphous, with an isostructurality index of 0.985. The azastyryl fragments are almost planar, with dihedral angles between the benzene and pyridine rings of ca 4.5 degrees. The rings of the benzyl groups are, in turn, almost perpendicular to the azastyryl planes, with dihedral angles larger than 80 degrees. The cations and anions are connected by O-H...X - (X = halogen) hydrogen bonds. The halide anions are `sandwiched' between the charged pyridinium rings of neighbouring molecules, and weak C-H...O hydrogen bonds and C-H...X and C-H...pi interactions also contribute to the crystal structures.