Structures of tetrabromothiophene and tetrabromoselenophene: the influence of the heteroatom on the heterophene packing

The crystal structures of C4Br4S and C4Br4Se have been determined from X-ray powder diffraction data, using directspace search techniques. In the case of C4Br4S two crystalline phases occur, a stable orthorhombic and a metastable monoclinic phase. For the orthorhombic phase two different structural models were found that fit the experimental data equally well. The diversity in crystal structure models and packings of C4Br4S is explained.