A hexafluoride is a chemical compound with the general formula XF₆. Sixteen elements are known to form stable hexafluorides. Nine of these elements are transition metals, three are actinides, and four are nonmetals or metalloids.

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, one is a liquid (Re), and the others are volatile solids. The p-block and group 6 hexafluorides are colorless, but the other hexafluorides have colors ranging from yellow to orange, red, brown, and black.

The molecular geometry is generally octahedral, with the exception of XeF₆, which is a fluxional molecule with a distorted octahedral structure which, according to valence shell electron pair repulsion theory, is 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 two of the bonds along one axis are longer or shorter than the other four), but this has not been verified experimentally.

The hexafluorides have a wide range of chemical reactivity. Sulfur hexafluoride is nearly inert and non-toxic. It has several applications due to its stability, dielectric properties, and high density (it is the densest non-toxic gas). Selenium hexafluoride is nearly as unreactive as SF₆, but tellurium hexafluoride is toxic, not very stable and can be hydrolyzed by water within 1 day. In contrast, metal hexafluorides are corrosive, readily hydrolyzed and may react violently with water. Some of them can be used as fluorinating agents. The metal hexafluorides have a high electron affinity, which makes them strong oxidizing agents. Platinum hexafluoride in particular is notable for its ability to oxidize the dioxygen molecule, O₂, to form dioxygenyl hexafluoroplatinate, and for being the first compound that was observed to react with xenon (see xenon hexafluoroplatinate).

Some metal hexafluorides find applications due to their volatility. Uranium hexafluoride is used in the uranium enrichment process to produce fuel for nuclear reactors. Fluoride volatility can also be exploited for nuclear fuel reprocessing. Tungsten hexafluoride is used in the production of semiconductors through the process of chemical vapor deposition.

The table below lists the main physical and structural properties of the hexafluorides.

Compound	m.p (°C)	b.p. (°C)	MW	solid ρ (g cm−1)	Bond (pm)	Color
Sulfur hexafluoride	−50.54	−63.8 (sublimes)	146.06	1.88 (−50 °C)	156.4	colorless
Selenium hexafluoride	−35 (2 atm)	−47 (sublimes)	192.9534		167–170	colorless
Tellurium hexafluoride	−38	−39	241.59		184	colorless
Xenon hexafluoride	49.25	75.6	245.28	3.56		colorless
Molybdenum hexafluoride	17.4	34	209.94	3.50 (−140 °C)	181.7	colorless
Technetium hexafluoride	37.4	55.3	(212)	3.58 (−140 °C)	181.2	yellow
Ruthenium hexafluoride	54		215.07	3.68 (−140 °C)	181.8	dark brown
Rhodium hexafluoride	70		216.91	3.71 (−140 °C)	182.4	black
Tungsten hexafluoride	1.9	17.1	297.85	4.86 (−140 °C)	182.6	colorless
Rhenium hexafluoride	18.5	33.7	300.2	4.94 (−140 °C)	182.6	yellow
Osmium hexafluoride	33		304.2	5.09 (−140 °C)	182.9	yellow
Iridium hexafluoride	44	53	306.2	5.11 (−140 °C)	183.4	yellow
Platinum hexafluoride	61.3	69.1	309.1	5.21 (−140 °C)	184.8	deep red
Uranium hexafluoride	64		352.0			white
Neptunium hexafluoride	54.7		(358)			orange
Plutonium hexafluoride	52		(356)			brown

References

• Drews, T; Supeł, J; Hagenbach, A; Seppelt, K (2006). "Solid state molecular structures of transition metal hexafluorides". Inorganic chemistry 45 (9): 3782–3788.
• Kirss, Rein U., Lamartine Meda. "Chemical Vapor Deposition of Tungsten Oxide." Applied Organometallic Chemistry 12 (1998): 155–160.
• Bartlett, N. "The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds". Angewandte Chemie International Edition in English 7 (6): 433-439.