Hexabromo‐ and hexaiododisilane: small and simple molecules showing completely different crystal structures

The title compounds were prepared through dephenylation of hexaphenyldisilane with acetyl bromide or acetyl iodide in the presence of the corresponding aluminium halide. Both substances were purified via sublimation and, for the first time, single crystals of hexabromodisilane, Si₂Br₆, and a new polymorph of hexaiododisilane, Si₂I₆, could be isolated. Molecules of Si₂Br₆ are located on a special position of site symmetry 2/m with a quarter of a molecule in the asymmetric unit. Molecules of Si₂I₆ are located on a special position of site symmetry with a sixth of a molecule in the asymmetric unit. The bond lengths of Si₂Br₆ and Si₂I₆ are in the usual ranges and both molecules adopt a staggered conformation. It is interesting to note that Si₂Br₆ and Si₂I₆ do not form isomorphous structures. Moreover, an orthorhombic polymorph of the present structure of Si₂I₆ is already known Jansen & Friede (1996). Acta Cryst. C 52 , 1333–1334]. Although the title compounds feature such small and simple molecules they show completely different crystal structures.