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.