Gas phase structures of chalcogen tetrahalides MX4 with M = S, Se, Te and X = F, Cl, Br, I

Abstract

Structural and conformational properties of the tetrahalides MX₄ with M = S, Se, Te and X = F, Cl, Br, I were studied with quantum chemical calculations (MP2/aug-cc-pVTZ and relativistic core potentials for heavy atoms). The pseudotrigonal bipyramidal geometries (C_2v symmetry) of the three tetrafluorides and of TeCl₄, whose structures have been determined by gas electron diffraction, are very well reproduced with this computational method. No additional stable conformer with C_3v, C_S, C_4v or T_d symmetry is predicted for these four chalcogen tetrahalides. For all other MX₄ compounds, except SeI₄, the existence of two conformers with C_2v and T_d symmetry is predicted. The T_d structure is favoured in the case of SI₄ and SeBr₄ and SeI₄ is predicted to exist only as T_d conformer.