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

Structural and conformational properties of the tetrahalides MX(4) 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 TeCl(4), 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 MX(4) compounds, except SeI(4), the existence of two conformers with C(2v) and T(d) symmetry is predicted. The T(d) structure is favoured in the case of SI(4) and SeBr(4) and SeI(4) is predicted to exist only as T(d) conformer.