Abstract Two polymorphic structures of rigid one-dimensional (1D) coordination polymers, [(HgBr 2) 2TPyP] · 2(1,1,2,2-tetrachloroethane, TCE) (1A, 1B), have been isolated in which the 1D polymers adopt either stacking or herringbone (or T-shaped) geometries as observed for simple aromatic hydrocarbons. Polymorph 1A has a 1D polymeric structure with each HgBr 2 tetrahedrally coordinated to a pyridyl moiety of two TPyP molecules. The 1D polymers in 1A are weakly cross-linked through long metal–halide bridges forming a 2D steplike sheet with each sheet stacked to form a continuous open porous structure. The 1D polymers in 1B adopt a T-shaped geometry such that the C–H groups of the pyrrole rings point toward the porphyrin cavity to maximize C–H ··· N or C–H ··· C interactions and the crest of the polymer (pyridyl–HgBr 2–pyridyl moiety) interdigitates into the supramolecular cavities to form long, but significant Hg ··· Br interactions. Indeed, the cause of the stacked versus herringbone structures in 1A and 1B can be traced to the different possible secondary interactions between Br and Hg: edge-on in 1A and side-on in 1B. (This is in contrast to the electrostatic interactions leading to face-to-face versus hydrogen bonding in edge-to-face aromatic packing.) Polymorph 1A crystallizes in the triclinic space group P-1 with a=7.3653(9), b=12.920(2), and c=14.320(2) Å, α=72.218(2), β=81.858(3), and γ=79.505(3)°, V=1270.5(3) Å 3, D calc=2.189 g cm −3, Z=1, and R=0.0672. Polymorph 1B is monoclinic, P2 1/ c with a=15.2397(2), b=30.4642(5), and c=11.2657(1) Å, β=93.212(1)°, V=5222.06(12) Å 3, D calc=2.131 g cm −3, Z=4, and R=0.0929.