Molybdenum hexafluoride
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Molybdenum hexafluoride
| Molybdenum hexafluoride | |
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-fluoride.svg) |
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Other names
molybdenum hexafluoride |
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| Identifiers | |
| CAS number | 7783-77-9  |
| PubChem | 82219 |
| EC number | 232-026-5 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | MoF6 |
| Molar mass | 209.93 g/mol |
| Appearance | white crystals[1] or colorless liquid hygroscopic |
| Density | 3.50 g/cm3[2] |
| Melting point |
17.5 °C[1] |
| Boiling point |
34.0 °C[1] |
| Solubility in water | hydrolyzes |
| Structure | |
| Crystal structure | Orthorhombic, oP28 |
| Space group | Pnma, No. 62 |
| Coordination geometry |
octahedral (Oh) |
| Dipole moment | 0 |
| Related compounds | |
| Other cations | Tungsten hexafluoride Uranium hexafluoride |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Molybdenum hexafluoride, also molybdenum(VI) fluoride, (MoF6) is the highest fluoride of molybdenum. It is a solid which melts just below room temperature; in water, it hydrolyses to give hydrofluoric acid.[3] It is one of the eighteen known binary hexafluorides.
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Contents
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Synthesis
Molybdenum hexafluoride is made by direct reaction of molybdenum metal in an excess of elemental fluorine gas.[2]
Description
Molybdenum hexafluoride is a liquid at room temperature. At 17.5 °C, it freezes into a white crystalline solid. The boiling point is 34.0 °C.[1]
The solid structure measured at −140 °C is 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.[2] The fluorine atoms are arranged in the hexagonal close packing.[4]
The MoF6 molecule itself (the form important for the liquid or gas phase) has octahedral molecular geometry, which has point group (Oh). The Mo–F bond length is 1.817 Å.[2]
Applications
Molybdenum hexafluoride has few uses, and generally appears as an impurity in uranium hexafluoride (in the nuclear industry, since molybdenum is a fission product of uranium) or tungsten hexafluoride (in the semiconductor industry; WF6 is used for chemical vapour deposition of tungsten, and MoF6 appears due to the chemical similarity of molybdenum and tungsten); it can be removed from the latter by reduction of a WF6-MoF6 mixture with any of a number of elements including molybdenum at moderately elevated temperature.[5][6]
References
- This article incorporates information from the German Wikipedia.
- ^ a b c d CRC Handbook of Chemistry and Physics, 90th Edition, CRC Press, Boca Raton, Florida, 2009, ISBN 978-1-4200-9084-0, Section 4, Physical Constants of Inorganic Compounds, p. 4-85.
- ^ a b c d T. Drews, J. Supeł, A. Hagenbach, K. Seppelt: "Solid State Molecular Structures of Transition Metal Hexafluorides", in: Inorganic Chemistry, 2006, 45 (9), S. 3782–3788; doi:10.1021/ic052029f; PMID 16634614
- ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.
- ^ J. H. Levy, J. C Taylor, A. B. Waugh: "Neutron Powder Structural Studies of UF6, MoF6 and WF6 at 77 K", in: Journal of Fluorine Chemistry, 1983, 23 (1), pp. 29–36; doi:10.1016/S0022-1139(00)81276-2.
- ^ US-Patent 5234679: Method of Refining Tungsten Hexafluoride Containing Molybdenum Hexafluoride as an Impurity, 10 August 1993.
- ^ US-Patent 6896866: Method for Purification of Tungsten Hexafluoride, 24 May 2005.
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