page_title: Compounds of fluorine
section_title: High oxidation state metal fluorides
hierarchical_section_title: Compounds of fluorine / Metal fluorides / High oxidation state metal fluorides
caption_attribution_description: English: Uranium hexafluoride crystals sealed in an ampoule, from http://web.ead.anl.gov/uranium/about/index.cfm
context_page_description: Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds.
  For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.
context_section_description: Metal penta- and higher fluorides are all molecular and hence at least somewhat volatile.
  Vanadium, niobium, and tantalum form pentafluorides as their highest charge-neutral fluoride. Vanadium pentafluoride is the only non-volatile high-charged metal fluoride, with vanadium being centers of –VF₆– octahedra. The niobium and tantalum pentafluorides, have the same tetrahedra in their structures, with the difference being the formation of the tetra- (rather than poly-) meric molecules.
  Bismuth's highest fluoride is a volatile penta species that is a powerful fluorinating agent. In the solid state, it is polymeric, consisting of linear chains of octahedra, sharing axial fluorides. In combination with alkali metals, pentavalent bismuth can form hexafluorobismuthate, [BiF₆]⁻, upon reaction with a fluoride donor, either strong (such as NaF) or not (such as XeF₄).
  Many metals that form hexafluorides also can form pentafluorides. For instance, uranium, which has a well-known hexafluoride, also forms two different pentafluoride structures. The room-temperature (alpha) form has the same linear chain structure as bismuth pentafluoride. As a molecular (gas) species, UF₅ has a square pyramidal structure.
  The metals that make well-characterized hexafluorides include nine metals in the center of the periodic table (molybdenum, technetium, ruthenium, rhodium, tungsten, rhenium, osmium, iridium, and platinum) along with elements 92–94: uranium, neptunium, and plutonium. At room temperature, tungsten hexafluoride is a gas. Molybdenum hexafluoride and rhenium hexafluoride are liquids. The rest are volatile solids.
  Metal hexafluorides are oxidants because of their tendency to release fluorines: for example, platinum hexafluoride was the first compound to oxidize molecular oxygen and xenon. Polonium also forms a hexafluoride, but it is understudied.
  Rhenium is the only metal known to bond with seven fluorides, which is the record for number of charged ligands for a charge-neutral metal compound. Rhenium heptafluoride adopts a pentagonal bipyramid molecular geometry. Calculations shows that the currently unknown but perhaps possible iridium heptafluoride (report of synthesis is being prepared), technetium heptafluoride, and osmium heptafluoride will also have this structure).
  Osmium octafluoride was first reported in 1913, but in 1958 that compound was shown to be actually osmium hexafluoride.  A 1993 theoretical study predicted very weak bonds in osmium octafluoride and said that it would be difficult to ever detect experimentally.  The study predicted that, if made, OsF₈ would have Os–F bonds of two different lengths.
caption: Uranium hexafluoride in sealed glass
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