Manganese(IV) fluoride
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| Names | |
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IUPAC name
manganese tetrafluoride
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| Other names
manganese(IV) fluoride
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| Identifiers | |
| ChemSpider | |
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| Properties | |
| MnF4 | |
| Molar mass | 130.93 g mol−1 |
| Appearance | blue solid |
| Density | 3.61 g cm−3 (calc.) |
| Melting point | 70 °C (158 °F; 343 K) decomposes |
| reacts violently | |
| Structure | |
| tetragonal, tI80 | |
| I41/a (No. 88) | |
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a = 1263 pm, c = 604.9 pm
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| Related compounds | |
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Other cations
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Manganese(II) fluoride Manganese(III) fluoride |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Manganese tetrafluoride, MnF4, is the highest fluoride of manganese. It is a powerful oxidizing agent and is used as a means of purifying elemental fluorine.
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.
Other preparations of MnF4 include the fluorination of MnF2 with krypton difluoride, or with F2 in liquid hydrogen fluoride solution under ultraviolet light. Manganese tetrafluoride has also been prepared (but not isolated) in an acid–base reaction between antimony pentafluoride and K2MnF6 as part of a chemical synthesis of elemental fluorine.
Manganese tetrafluoride is in equilibrium with manganese(III) fluoride and elemental fluorine:
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 about 10−4 Pa (10−9 bar), and the enthalpy change of reaction at +44(8) kJ mol−1.
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