Manganese(III) fluoride

Manganese(III) fluoride (also known as Manganese trifluoride) is the inorganic compound with the formula MnF₃. 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

MnF₃ can be prepared by treating a solution of MnF₂ in hydrogen fluoride with fluorine:

MnF₂ + 0.5 F₂ → MnF₃

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

Structure

Like vanadium(III) fluoride, MnF₃ 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 MnF₃^.3H₂O is obtained by crystallisation of MnF₃ from hydrofluoric acid. The hydrate exists as two polymorphs, with space groups P2₁/c and P2₁/a. Each consists of the salt [Mn(H₂O)₄F₂]⁺[Mn(H₂O)₂F₄]⁻ ).

Reactions

MnF₃ is Lewis acidic and forms a variety of derivatives. One example is K₂MnF₃(SO₄). MnF₃ reacts with sodium fluoride to give the octahedral hexafluoride:

3NaF + MnF₃ → Na₃MnF₆

Related reactions salts of the anions MnF₅²⁻ or MnF₄⁻. These anions adopt chain and layer structures respectively, with bridging fluoride. Manganese remains 6 coordinate, octahedral, and trivalent in all of these materials.

Manganese(III) fluoride fluorinates organic compounds including aromatic hydrocarbons, cyclobutenes, and fullerenes.

On heating, MnF₃ decomposes to manganese(II) fluoride.

MnF₃ is a source of MnCl₃ complexes by reaction with bismuth trichloride.

See also

• CoF₃, 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. 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. 521–525, google books

External links

• National Pollutant Inventory: Fluoride and compounds fact sheet
• National Pollutant Inventory: Manganese and compounds Fact Sheet