Cadmium and mercury dihalides were reacted with benzopyridine- and benzopyrazine-type N-donor ligands as Lewis bases. The solid-state structures of 13 novel reaction products were studied by X-ray diffraction. Eleven of the structures can be classified as one-dimensional halide-bridged polymers of composition [M(μ-X)₂(L)]_∞, in which the metal ion displays a coordination number of five, while the remaining two structures exhibit one-dimensional dimers that are linked by long, semi-coordinate M–X⋯M–X interactions to form pseudo-halide-bridged polymers. Four of the structures contain Cd²⁺ as the metal ion, while the remaining nine have Hg²⁺ as the metal ion. Although all the halide-bridged polymers show a coordination number of five, two different metal cation geometries are displayed. A detailed comparison of all structural results, which includes related compounds from the literature and allows for the study of the effect of an increase in the width of the N-donor ligand on the halide-bridged chain geometries and other structural features, concludes the discussion.