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

The crystal structures of C(4)Br(4)S and C(4)Br(4)Se have been determined from X-ray powder diffraction data, using direct-space search techniques. In the case of C(4)Br(4)S 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 C(4)Br(4)S is explained.