Binary Hexafluorides
Seventeen elements are known to form hexafluorides. Nine of these elements are transition metals, three are actinides, four are chalcogens, and one is a noble gas.Most hexafluorides are molecular compounds with low melting and boiling points. Four hexafluorides (S, Se, Te, and W) are gases at room temperature (25 °C) and a pressure of 1 atm, two are liquid (Re, Mo), and the others are volatile solids. The group 6, chalcogen, and noble gas hexafluorides are colourless, but the other hexafluorides have colours ranging from white, through yellow, orange, red, brown, and grey, to black.
The molecular geometry is generally octahedral, though it is sometimes distorted. XeF6 is a fluxional molecule with a distorted octahedral structure, which is, according to VSEPR theory, caused by the non-bonding lone pair. In the solid state, XeF6 has a complex structure involving tetramers and hexamers. According to quantum chemical calculations, ReF6 and RuF6 should have tetragonally distorted structures (where the two bonds along one axis are longer or shorter than the other four), but this has not been verified experimentally.
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