Manganese(III) fluoride


Manganese fluoride 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:
It can also be prepared by the reaction of elemental fluorine with a manganese halide at ~250 °C.

Structure

Like vanadium fluoride, MnF3 features octahedral metal centers with the same average M-F bond distances. In the Mn compound, however, is distorted 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.

Reactions

MnF3 is Lewis acidic and forms a variety of derivatives. One example is K2MnF3. MnF3 reacts with [sodium fluoride to give the octahedral hexafluoride:
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 fluoride fluorinates organic compounds including aromatic hydrocarbons, cyclobutenes, and fullerenes.
On heating, MnF3 decomposes to manganese fluoride.