Hexafluoride

The hexafluoride are a group of chemical compounds with the formula XF6. From 16 elements stable hexafluoride are known. 9 of these elements belong to the transition metals, actinides to 3, and 4 are non-metals.

Properties

Physical Properties

Most hexafluoride are covalent compounds with low melting and boiling points. 4 hexafluoride (S, Se, Te, W) at room temperature (25 ° C.) and atmospheric pressure (1013 mbar) gas, 2 are liquid (Re, Mo), the others are volatile solids. 4 hexafluoride (S, Se, Te, U) go over directly into the gaseous state when heated by sublimation. The Hexafluoride the main group (S, Se, Te, Xe ) and the subgroup 6 ( Mo, W) are colorless, the colors of the other hexafluoride move in areas from yellow to orange, red, brown and black.

Molecular structure

The molecular geometry is usually octahedral, an exception is xenon hexafluoride. The connection is square - bipyramidal ( distorted octahedral) built. The structure forms according to VSEPR theory, due to the remaining lone pair a pentagonal- pyramidal molecule. Due to quantum mechanical calculations and ReF6 RuF6 should tetragonally distorted structures have ( in which the two bonds of an axis are longer or shorter than that of the other four ), but so far this has not been observed.

Chemical Properties

The hexafluoride offer a broad spectrum of chemical reactivity. Sulfur hexafluoride is almost inert and nontoxic. Because of its stability, dielectric properties and high density, it has numerous applications. Selenium hexafluoride is nearly as unreactive as SF6, whereas tellurium hexafluoride is toxic, not very stable and can be hydrolyzed by water within a day. In contrast, the metal hexafluoride are corrosive, easily hydrolyzable and may react violently with water. Some of them can be used as a fluorinating agent. The metal hexafluoride have a high electron affinity, which makes it strong oxidants. Platinum hexafluoride is distinguished by its ability to oxidize the oxygen molecule (O2). Therefore, it was the first compound was reacted with xenon to the reaction (see Xenonhexafluoroplatinat ).

Use

Some of the metal hexafluoride find practical applications because of their volatility. Uranium hexafluoride is used for uranium enrichment to win as fuel for nuclear reactors. The Fluoridflüchtigkeit is used also for the reprocessing of nuclear fuels. Tungsten hexafluoride is used in the process of chemical vapor deposition in semiconductor manufacturing.

More hexafluoride

The synthesis of polonium hexafluoride ( PoF6 ) was attempted in 1945, but did not lead to clear results, the boiling point was estimated to be -40 ° C. Ab initio and Dirac - Hartree-Fock calculations describe some properties of the not yet synthesized radon hexafluoride ( RNF6 ). Americiumhexafluorid ( AmF6 ) could not be shown by direct fluorination of americium (IV ) fluoride; Also in 1990, the synthesis is not yet done.