2,2 ',6,6 '-Tetrachloro-4,4 '-propane2,2-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, C15H12Cl4O2, can be descr ibed as a packing of sheets. The packing shows a very short intermolecular Cl . . . Cl contact distance of 3.094 (2) Angstrom between pairs of molecul es inside each sheet. The crystal structure of 2,2',6-tribromo-4,4'-propane -2,2-diyldiphenol, C15H13Br3O2, can be described as a packing of doubly str anded helical square tubes. These square helices are interconnected through Br . . . Br contacts between different helices. Finally, a previously know n structure, 2,2',6,6'-tetrabromo-4,4'-propane-2,2-diyldiphenol [Simonov, C heban, Rotaru & Bels'skii (1986). Kristallografiya, 31, 397-399], C15H12Br4 O2, which is the most commonly used flame retardant and which has twofold r otational 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.