Formula MoF6 Density 2.54 g/cm³ | Molar mass 209.93 g/mol | |
 | ||
Appearance white crystals or colorless liquid; hygroscopic | ||
Molybdenum hexafluoride, also molybdenum(VI) fluoride is the inorganic compound with the formula MoF6. It is the highest fluoride of molybdenum. A colourless solid, it melts just below room temperature. It is highly unstable toward hydrolysis. It is one of the seventeen known binary hexafluorides.
Contents
Synthesis
Molybdenum hexafluoride is made by direct reaction of molybdenum metal in an excess of elemental fluorine gas.
Mo + 3 F2 → MoF
6
Typical impurities are MoO2F2 and MoOF4.
Description
Molybdenum hexafluoride is a liquid at room temperature. It reacts violently with water with release of hydrofluoric acid and molybdenum oxides.
At −140 °C, it crystallizes in the orthorhombic space group Pnma. Lattice parameters are a = 9.394 Å, b = 8.543 Å, and c = 4.959 Å. There are four formula units (in this case, discrete molecules) per unit cell, giving a density of 3.50 g·cm−3. The fluorine atoms are arranged in the hexagonal close packing.
In liquid and gas phase, MoF6 adopt octahedral molecular geometry with point group Oh. The Mo–F bond length is 1.817 Å.
Applications
Molybdenum hexafluoride has few uses. In the nuclear industry, MoF6 occurs as an impurity in uranium hexafluoride since molybdenum is a fission product of uranium. It is also an impurity in tungsten hexafluoride, which is used in the semiconductor industry. MoF6 can be removed by reduction of a WF6-MoF6 mixture with any of a number of elements including molybdenum at moderately elevated temperature.