Q. Describe about tetrahalides?

S, Se, Te and Po form tetrahalides with all the halogens. However, tetrafluoride of polonium, tetrabromide of sulphur and tetraiodides of sulphur and selenium are not formed. The tetrahalides are formed mainly by the reaction between the corresponding elements, e.g.,

Te + 2Cl₂ ------------> TeCl₄

These are covalent compounds which hydrolyse to give the corresponding dioxides.

SeBr₄ + 2H₂O--------------> SeO₂+ 4HBr

SF₄+ 2H₂O-------------------> SO₂ + 4HF

As stated' above, the tetrahalides dissociate in solution or in the vapour state to the corresponding dihalides.

SeCl₄----------------------------> SeCl₂ + Cl₂

The tetrahalides also form complex anions of, the type EX^2-₆ in the presence of excess of the corresponding halogen acid.

SeCl₄ + 2HCl -----------------------------------> H₂SeCl₆

There has been much controversy concerning the structure of tetrahalides. The presently accepted structure of SF₄, and SeF₄, is see-saw with one equatorial position occupied by an electron pair as shown in Fig.