The asymmetric unit of the polymeric title compound, {(C21H19N2)[HgCl3]} n , comprises one-half of the cationic mol-ecule, the other half being generated by application of twofold rotation symmetry, one Hg and two Cl atoms. The Hg(II) atom, lying on a twofold rotation axis, exhibits a distorted triangular coordination environment and is surrounded by three Cl atoms with Hg-Cl distances in the range 2.359 (2)-2.4754 (13) Å. Two additional longer distances [Hg⋯Cl = 3.104 (14) Å] lead to the formation of polymeric [HgCl1/1Cl4/2](-) chains extending along [001]. The crystal packing can be described by cationic layers alternating parallel to (-110) with the anionic chains located between the layers. The packing is consolidated by π-π stacking inter-actions between the benzene rings of the central benzimidazole entities, with centroid-to-centroid distances of 3.643 (3) Å.
Keywords: benzimidazole derivative; crystal structure; trichloridomercurate.