Reaction of the ligand 2,2 0 -biquinoline (bq) with Zn(ClO 4 ) 2 , CdCl 2 and Hg(SCN) 2 gives complexes [Zn(bq) 2 ] (ClO 4 ) 2 , [Cd(bq) 2 Cl 2 ] and [Hg(bq)(SCN) 2 ] which were characterized by elemental analyses and IR spectroscopy. The crystal structure of [Hg(bq)(SCN) 2 ] was determined by X-ray crystallography. The complex comprises a monomeric Hg(SCN) 2 unit with one 2,2 0 -biquinoline (bq) ligand coordinated to the Hg atom via the two quinolinic nitrogens, giving rise to a five-membered chelate ring in a distorted tetrahedral environment. A -stacking interaction exists between the parallel aromatic rings in adjacent chains, resulting in a planar species in which the mean molecular planes are close to parallel and separated by a distance of $3.5 Å , close to that of the planes in graphite.