Sulphur forms many compounds, in a range of oxidation states, with the halides. Oxygen forms only OF2 and O2F2.
The maximum oxidation state of sulphur, +6, is only achieved in combination with F, forming SF6. The sulphur fluorides in lower oxidation states are unstable with respect to formation of SF6 and fluorine.
The structures of the fluorides are all as predicted by VSEPR. For example, the SF4 molecule has 10 electrons around the central S atom, and hence a trigonal bipyramidal structure is adopted, with the lone pair in the larger equatorial position.
| SF2:[OS(S) = +2] | SF4:[OS(S) = +4] | S2F10:[OS(S) = +5] | SF6:[OS(S) = +6] |
The +2 oxidation state is demonstrated by SCl2, and further examples of the above oxidation states are: S2Cl2 [+1], SeX4 (X = F,Cl,Br) and TeX4 (X = F,Cl,Br,I) [+4], Se2F10 [+5], SeF6 and TeF6 [+6].
Reactions of Sulphur Halides
SF6: The six fluoride atoms around the central sulphur atom form a steric block to reaction. It is therefore inert, and is a gas at room temperature. This inertness prevents it from undergoing otherwise thermodynamically favourable reactions such as hydrolysis.
SF4: This is less sterically crowded than SF6, and so undergoes reactions more readily. Partial hydrolysis occurs rapidly (1). It also acts as a fluorinating agent, and converts carbonyl and phosphoryl groups to CF2 and PF2 respectively (2).