Packing of tetrahedral EX4 molecules with E = C, Si, Ge, Sn, Pb and X = F, Cl, Br, I

The crystal structures of EX4 molecules with E = C, Si, Ge, Sn, Pb and X = F, Cl, Br and I were investigated by geometrical packing analysis, lattice-energy minimisations and analysis of the halogen–halogen interactions. The 18 known crystal structures group into seven different structure types. In most cases the halogen atoms as well as the molecules themselves are arranged in distorted close-sphere packings. The sphericity of the molecules seems to determine which structure types are adopted by the individual compounds. Lattice-energy minimisations show a high number of possible polymorphs. For EX4 compounds the same types of halogen–halogen interactions as for halogenated organic compounds were found but with different ranges for the E–X⋯X angle values.