2,2',6,6'-Tetrachloro-4,4'-propane-2,2-diyldiphenol, 2,2',6-tribromo-4,4'-propane-2,2-diyldiphenol and 2,2',6,6'-tetrabromo-4,4'-propane-2,2-diyldiphenol.

Three flame retardants with very similar molecular structures showing three different packing patterns have been studied. The crystal structure of 2,2',6,6'-tetrachloro-4,4'-propane-2,2-diyldiphenol, C(15)H(12)Cl(4)O(2), can be described as a packing of sheets. The packing shows a very short intermolecular Cl.Cl contact distance of 3.094 (2) A between pairs of molecules inside each sheet. The crystal structure of 2,2',6-tribromo-4,4'-propane-2,2-diyldiphenol, C(15)H(13)Br(3)O(2), can be described as a packing of doubly stranded helical square tubes. These square helices are interconnected through Br...Br contacts between different helices. Finally, a previously known structure, 2,2',6,6'-tetrabromo-4,4'-propane-2,2-diyldiphenol [Simonov, Cheban, Rotaru & Bels'skii (1986). Kristallografiya, 31, 397-399], C(15)H(12)Br(4)O(2), which is the most commonly used flame retardant and which has twofold rotational symmetry, has been refined in the correct absolute configuration. The structure shows large differences from the chloro analogue with regard to packing, van der Waals distances and hydrogen-bond distances.