Molybdenum hexafluoride

Molybdenum hexafluoride, also molybdenum(VI) fluoride, is the inorganic compound with the formula MoF₆. It is the highest fluoride of molybdenum. It is a colourless solid and melts just below room temperature and boils in 34 °C.^[3] It is one of the seventeen known binary hexafluorides.

Molybdenum hexafluoride

Names
IUPAC names molybdenum(VI) fluoride
Other names molybdenum hexafluoride
Identifiers
CAS Number	7783-77-9 Y
3D model (JSmol)	Interactive image
ChemSpider	74199
ECHA InfoCard	100.029.114
EC Number	232-026-5
PubChem CID	82219
UNII	ZLT5J123W3 Y
CompTox Dashboard (EPA)	DTXSID0064834
InChI InChI=1S/6FH.Mo/h6*1H;/q;;;;;;+6/p-6
SMILES F[Mo](F)(F)(F)(F)F
Properties
Chemical 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 (63.5 °F; 290.6 K)[1]
Boiling point	34.0 °C (93.2 °F; 307.1 K)[1]
Solubility in water	hydrolyzes
Magnetic susceptibility (χ)	−26.0·10−6 cm3/mol
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 Molybdenum(VI) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Synthesis

Molybdenum hexafluoride is made by direct reaction of molybdenum metal in an excess of elemental fluorine:^[2]

Mo + 3 F
₂ → MoF
₆

The compound hydrolyzes easily,^[4] and typical impurities are MoO₂F₂ and MoOF₄.^[5]

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.^[2] The fluorine atoms are arranged in the hexagonal close packing.^[6]

In liquid and gas phase, MoF₆ adopt octahedral molecular geometry with point group O_h. The Mo–F bond length is 1.817 Å.^[2]

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.^[4] 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.^[7][8]

References

1. 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.
2. 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
3. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
4. 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
5. W. Kwasnik "Molybdenum(VI) Fluoride" Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 259.
6. 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.
7. 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
8. US-Patent 6896866: Method for Purification of Tungsten Hexafluoride Archived 2011-06-12 at the Wayback Machine, 24 May 2005.