Molybdenum hexafluoride, also molybdenum(VI) fluoride, is an inorganic compound with the formula MoF6. It is the fluoride of molybdenum in its highest oxidation state of +6. It is a colourless solid that melts just below room temperature and boils at 34 °C. It is one of the seventeen known binary hexafluorides.
Synthesis
Molybdenum hexafluoride is made by direct reaction of molybdenum metal in an excess of elemental fluorine:2
Mo + 3 F2 → MoF6The compound hydrolyzes easily,3 and typical impurities are MoO2F2 and MoOF4.4
Description
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−3.5 The fluorine atoms are arranged in the hexagonal close packing.6
In liquid and gas phase, MoF6 adopt octahedral molecular geometry with point group Oh. The Mo–F bond length is 1.817 Å.7
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.
The semiconductor industry constructs various integrated circuits through chemical vapor deposition of molybdenum hexafluoride.8 In some cases, the deposited molybdenum is an impurity in the intended tungsten hexafluoride. MoF6 can be removed by reduction of a WF6-MoF6 mixture with any of a number of elements including hydrogen iodide at moderately elevated temperature.910
References
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. 978-0-08-037941-8 ↩
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 /wiki/Inorg._Chem. ↩
Meshri, Dayal T. (2000), "Fluorine compounds, inorganic, molybdenum", Kirk-Othmer Encyclopedia of Chemical Technology, New York: John Wiley, doi:10.1002/0471238961.1315122513051908.a01, ISBN 9780471238966 9780471238966 ↩
W. Kwasnik "Molybdenum(VI) Fluoride" Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 259. ↩
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 /wiki/Inorg._Chem. ↩
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. /w/index.php?title=Journal_of_Fluorine_Chemistry&action=edit&redlink=1 ↩
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 /wiki/Inorg._Chem. ↩
Meshri, Dayal T. (2000), "Fluorine compounds, inorganic, molybdenum", Kirk-Othmer Encyclopedia of Chemical Technology, New York: John Wiley, doi:10.1002/0471238961.1315122513051908.a01, ISBN 9780471238966 9780471238966 ↩
US-Patent 5234679: Method of Refining Tungsten Hexafluoride Containing Molybdenum Hexafluoride as an Impurity Archived 2011-06-12 at the Wayback Machine, 10 August 1993 http://www.patentstorm.us/patents/5234679/description.html ↩
US-Patent 6896866: Method for Purification of Tungsten Hexafluoride Archived 2011-06-12 at the Wayback Machine, 24 May 2005. http://www.patentstorm.us/patents/6896866/description.html ↩