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In poly[di-μ-chlorido-μ-(4,4′-bipyridazine)-κ2N1:N1′-cadmium(II)], [CdCl2(C8H6N4)]n, (I), and its isomorphous bromide analogue, [CdBr2(C8H6N4)]n, (II), the halide atom lies on a mirror plane and the CdII ion resides at the intersection of two perpendicular mirror planes with m2m site symmetry. The pyridazine rings of the ligand lie in a mirror plane and are related to each other by a second mirror plane perpendicular to the first. The compounds adopt the characteristic structure of the [MIIX2(bipy)] type (bipy is bipyridine) based on crosslinking of [Cd(μ-X)2]n chains [Cd—Cl = 2.5955 (9) and 2.6688 (9) Å; Cd—Br = 2.7089 (4) and 2.8041 (3) Å] by bitopic rod-like organic ligands [Cd—N = 2.368 (3)–2.380 (3) Å]. This feature is discussed in terms of supramolecular stabilization, implying that the periodicity of the inorganic chain [Cd...Cd = 3.7802 (4) Å in (I) and 3.9432 (3) Å in (II)] is favourable for extensive parallel π–π stacking of monodentate pyridazine rings, with centroid–centroid distances of 3.7751 (4) Å in (I) and 3.9359 (4) Å in (II). This is not the case for the longer iodide bridges, which cannot stabilize such a pattern. In poly[tetra-μ-iodido-μ4-(4,4′-bipyridazine)-κ4N1:N2:N1′:N2′-dicadmium(II)], [Cd2I4(C8H6N4)]n, (III), the ligands are situated across a centre of inversion; they are tetradentate [Cd—N = 2.488 (2) and 2.516 (2) Å] and link successive [Cd(μ-I)2]n chains [Cd—I = 2.8816 (3)–3.0069 (4) Å] into corrugated layers.