Technetium hexafluoride or technetium(VI) fluoride ( Tc F₆) is a yellow inorganic compound with a low

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

. It was first identified in 1961. In this compound, technetium has an

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

of +6, the highest oxidation state found in the technetium halides. In this respect, technetium differs from rhenium, which forms a heptafluoride, ReF₇. Technetium hexafluoride occurs as an impurity in

uranium hexafluoride Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...

, as technetium is a fission product of

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

( spontaneous fission in natural uranium, possible contamination from induced fission inside the reactor in

reprocessed uranium Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material s ...

). The fact that the boiling point of the hexafluorides of uranium and technetium are very close to each other presents a problem in using

fluoride volatility Fluoride volatility is the tendency of highly fluorinated molecules to vaporize at comparatively low temperatures. Heptafluorides, hexafluorides and pentafluorides have much lower boiling points than the lower- valence fluorides. Most difluor ...

in nuclear reprocessing.

Preparation

Technetium hexafluoride is prepared by heating technetium metal with an excess of F₂ at 400 °C. :Tc + 3 →

Description

Technetium hexafluoride is a golden-yellow solid at room temperature. Its melting point is 37.4 °C and its boiling point is 55.3 °C. Technetium hexafluoride undergoes a solid

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...

at −4.54 °C. Above this temperature (measured at 10 °C), the solid structure is cubic. Lattice parameters are ''a'' = 6.16 Å. There are two

formula unit In chemistry, a formula unit is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. E ...

s (in this case, discrete molecules) per

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

, giving a density of 3.02 g·cm⁻³. Below this temperature (measured at −19 °C), the solid structure is orthorhombic space group ''Pnma''. Lattice parameters are ''a'' = 9.55 Å, ''b'' = 8.74 Å, and ''c'' = 5.02 Å. There are four

s (in this case, discrete molecules) per

, giving a density of 3.38 g·cm⁻³. At −140 °C, the solid structure is still orthothombic, but the lattice parameters are now ''a'' = 9.360 Å, ''b'' = 8.517 Å, and ''c'' = 4.934 Å, giving a density of 3.58 g·cm⁻³. The TcF₆ molecule itself (the form important for the liquid or gas phase) has octahedral molecular geometry, which has point group ('' O_h''). The Tc–F

bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...

is 1.812 Å. Its

magnetic moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagne ...

has been measured to be 0.45 ''μ''_B.

Properties

Physical

TcF₆ is

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...

, as shown by

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

and Raman spectra. Its low-temperature orthorhombic form converts to the higher symmetry

body-centred cubic In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties of ...

form at room temperature, like other metal hexafluorides such as RhF₆ and OsF₆. Preliminary measurements of

yield a value of 0.45 µB, which is lower than expected for a d¹ octahedral compound.

Chemical

TcF₆ reacts with alkaline

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride sa ...

s in

iodine pentafluoride Iodine pentafluoride is an interhalogen compound with chemical formula IF5. It is one of the fluorides of iodine. It is a colorless liquid, although impure samples appear yellow. It is used as a fluorination reagent and even a solvent in special ...

(IF₅) solution to form hexafluorotechnetates. TcF₆ disproportionates on

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

with aqueous

NaOH Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

to form a black precipitate of TcO₂. In hydrogen fluoride solution, TcF₆ reacts with hydrazinium fluoride to yield N₂H₆TcF₆ or N₂H₆(TcF₆)₂.

References

{{fluorine compounds Technetium compounds Hexafluorides Octahedral compounds