Manganese tetrafluoride was first unequivocally prepared in 1961 by the reaction of manganese(II) fluoride (or other MnII compounds) with a stream of fluorine gas at 550 °C: the MnF4 sublimes into the gas stream and condenses onto a cold finger. This is still the commonest method of preparation, although the sublimation can be avoided by operating at increased fluorine pressure (4.5–6 bar at 180–320 °C) and mechanically agitating the powder to avoid sintering of the grains. The reaction can also be carried out starting from manganese powder in a fluidized bed.
Decomposition is favoured by increasing temperature, and disfavoured by the presence of fluorine gas, but the exact parameters of the equilibrium are unclear, with some sources saying that MnF4 will decompose slowly at room temperature, others placing a practical lower temperature limit of 70 °C, and another claiming that MnF4 is essentially stable up to 320 °C. The equilibrium pressure of fluorine above MnF4 at room temperature has been estimated at 10−4 Pa (10−9 bar), and the enthalpy change of reaction at +44(8) kJ mol−1.
Reaction with alkali metal fluorides or concentrated hydrofluoric acid gives the yellow hexafluoromanganate(IV) anion [MnF6]2−.
The main application of manganese tetrafluoride is in the purification of elemental fluorine. Fluorine gas is produced by electrolysis of anhydrous hydrogen fluoride (with a small amount of potassium fluoride added as a support electrolyte) in a Moissan cell. The technical product is contaminated with HF, much of which can be removed by passing the gas over solid KF, but also with oxygen (from traces of water) and possibly heavy-metal fluorides such as arsenic pentafluoride (from contamination of the HF). These contaminants are particularly problematic for the semiconductor industry, which uses high-purity fluorine for etching silicon wafers. Further impurities, such as iron, nickel, gallium and tungsten compounds, can be introduced if unreacted fluorine is recycled.
The technical-grade fluorine is purified by reacting it with MnF3 to form manganese tetrafluoride. As this stage, any heavy metals present will form involatile complex fluorides, while the HF and O2 are unreactive. Once the MnF3 has been converted, the excess gas is vented for recycling, carrying the remaining gaseous impurities with it. The MnF4 is then heated to 380 °C to release fluorine at purities of up to 99.95%, reforming MnF3, which can be reused. By placing two reactors in parallel, the purification process can be made continuous, with one reactor taking in technical fluorine while the other delivers high-grade fluorine. Alternatively, the manganese tetrafluoride can be isolated and transported to where the fluorine is needed, at lower cost and greater safety than pressurized fluorine gas.
WO patent 2006033480, Torisu, Junichi; Oka, Masakazu & Kuznetsov, Andrey Sergeyevich et al., "Method of manufacturing manganese tetrafluoride", published 2006-03-30, assigned to Astor Electronics and Showa Denko . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006033480
WO patent 2009074562, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Process for the purification of elemental fluorine", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074562
Reports of the preparation of MnF4 date back to the nineteenth century,[6] but are inconsistent with the now-known chemistry of the genuine compound.
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WO patent 2006033480, Torisu, Junichi; Oka, Masakazu & Kuznetsov, Andrey Sergeyevich et al., "Method of manufacturing manganese tetrafluoride", published 2006-03-30, assigned to Astor Electronics and Showa Denko . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006033480
WO application 2009074560, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Method for preparing manganese tetrafluoride", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074560
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WO patent 2006033480, Torisu, Junichi; Oka, Masakazu & Kuznetsov, Andrey Sergeyevich et al., "Method of manufacturing manganese tetrafluoride", published 2006-03-30, assigned to Astor Electronics and Showa Denko . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006033480
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These two results are inconsistent with one another, as ΔrHo would have to be about +80 kJ mol−1 for peq(F2) ≈ 10−9 bar at 298 K, given that the overwhelming contribution to ΔrSo is So(F2) = 202.791(5) J K−1 mol−1.[19] The quoted value of ΔrHo is consistent with most reported decomposition temperatures.
Hoppe, Rudolf; Dähne, Wolfgang; Klemm, Wilhelm (1961), "Mangantetrafluorid, MnF4", Naturwissenschaften, 48 (11): 429, Bibcode:1961NW.....48..429H, doi:10.1007/BF00621676, S2CID 30724467. /wiki/Rudolf_Hoppe
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WO patent 2009074562, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Process for the purification of elemental fluorine", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074562
WO patent 2006033480, Torisu, Junichi; Oka, Masakazu & Kuznetsov, Andrey Sergeyevich et al., "Method of manufacturing manganese tetrafluoride", published 2006-03-30, assigned to Astor Electronics and Showa Denko . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006033480
WO patent 2009074562, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Process for the purification of elemental fluorine", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074562
WO patent 2009074562, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Process for the purification of elemental fluorine", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074562
WO patent 2006033480, Torisu, Junichi; Oka, Masakazu & Kuznetsov, Andrey Sergeyevich et al., "Method of manufacturing manganese tetrafluoride", published 2006-03-30, assigned to Astor Electronics and Showa Denko . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006033480
WO application 2009074560, Seseke-Koyro, Ulrich; Garcia-Juan, Placido & Palsherm, Stefan et al., "Method for preparing manganese tetrafluoride", published 2009-06-18, assigned to Solvay Fluor . https://worldwide.espacenet.com/textdoc?DB=EPODOC&IDX=WO2009074560
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