Manganese(III) fluoride (also known as Manganese trifluoride) is the inorganic compound with the formula MnF<sub>3</sub>. This red/purplish solid is useful for converting hydrocarbons into fluorocarbons, i.e., it is a fluorination agent. It forms a hydrate and many derivatives.

Synthesis, structure and reactions

MnF<sub>3</sub> can be prepared by treating a solution of MnF<sub>2</sub> in hydrogen fluoride with fluorine:

:MnF<sub>2</sub> + 0.5 F<sub>2</sub> → MnF<sub>3</sub>

It can also be prepared by the reaction of elemental fluorine with a manganese(II) halide at ~250&nbsp;°C.

Structure

Like vanadium(III) fluoride, MnF<sub>3</sub> features octahedral metal centers with the same average M-F bond distances. In the Mn compound, however, is distorted (and hence a monoclinic unit cell vs. a higher symmetry one) due to the Jahn-Teller effect, with pairs of Mn-F distances of 1.79, 1.91, 2.09 Å.

The hydrate MnF<sub>3</sub><sup>.</sup>3H<sub>2</sub>O is obtained by crystallisation of MnF<sub>3</sub> from hydrofluoric acid. The hydrate exists as two polymorphs, with space groups P2<sub>1</sub>/c and P2<sub>1</sub>/a. Each consists of the salt [Mn(H<sub>2</sub>O)<sub>4</sub>F<sub>2</sub>]<sup>+</sup>[Mn(H<sub>2</sub>O)<sub>2</sub>F<sub>4</sub>]<sup>−</sup> ).

Reactions

MnF<sub>3</sub> is Lewis acidic and forms a variety of derivatives. One example is K<sub>2</sub>MnF<sub>3</sub>(SO<sub>4</sub>). MnF<sub>3</sub> reacts with sodium fluoride to give the octahedral hexafluoride: cyclobutenes, and fullerenes.

On heating, MnF<sub>3</sub> decomposes to manganese(II) fluoride.

MnF<sub>3</sub> is a source of MnCl<sub>3</sub> complexes by reaction with bismuth trichloride.

See also

  • CoF<sub>3</sub>, another fluorinating agent based on a transition metal in an oxidising +3 state.

References

Further reading

  • Novel syntheses of some binary fluorides: the role of anhydrous hydrogen fluoride Acta Chim. Slov. 1999, 46(2), pp.&nbsp;229–238, Zoran Mazej, Karel Lutar and Boris Žemva
  • Knudsen Cell mass spectrometry study of Manganese Trifluoride vaporisation, High temperature corrosion and materials chemistry IV: proceedings of the International Symposium, pp.&nbsp;521–525, google books
  • National Pollutant Inventory: Fluoride and compounds fact sheet
  • National Pollutant Inventory: Manganese and compounds Fact Sheet