Magnesium fluoride

Magnesium fluoride is an inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs naturally as the rare mineral sellaite.

Magnesium fluoride[1]
Magnesium fluoride
Names
Other names
Sellaite
Irtran-1
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.086
EC Number
  • 231-995-1
RTECS number
  • OM3325000
UNII
  • InChI=1S/2FH.Mg/h2*1H;/q;;+2/p-2 checkY
    Key: ORUIBWPALBXDOA-UHFFFAOYSA-L checkY
  • InChI=1/2FH.Mg/h2*1H;/q;;+2/p-2
    Key: ORUIBWPALBXDOA-NUQVWONBAK
  • F[Mg]F
  • [Mg+2].[F-].[F-]
Properties
MgF2
Molar mass 62.3018 g/mol
Appearance White tetragonal crystals
Density 3.148 g/cm3
Melting point 1,263 °C (2,305 °F; 1,536 K)
Boiling point 2,260 °C (4,100 °F; 2,530 K)
0.013 g/(100 mL)
5.16⋅10−11
Solubility
−22.7⋅10−6 cm3/mol
1.37397
Structure
Rutile (tetragonal), tP6
P42/mnm, No. 136
Thermochemistry
61.6 J⋅mol−1⋅K−1
57.2 J⋅mol−1⋅K−1
−1124.2 kJ⋅mol−1
−1071 kJ/mol
Hazards[2][3]
GHS labelling:
Irritant
Warning
H303, H315, H319, H335
P261, P304+P340, P305+P351+P338, P405
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
3
0
0
Lethal dose or concentration (LD, LC):
2330 (rat, oral)
Safety data sheet (SDS) ChemicalBook
Related compounds
Other anions
Other cations
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

Production

Magnesium fluoride is prepared from magnesium oxide with sources of hydrogen fluoride such as ammonium bifluoride:

MgO + [NH4]HF2 → MgF2 + NH3 + H2O

Related metathesis reactions are also feasible:

Mg(OH)2 + CuF2 → MgF2 + Cu(OH)2

Structure

The compound crystallizes as tetragonal birefringent crystals. The structure of the magnesium fluoride is similar to that of rutile,[4][5] featuring octahedral Mg2+ cations and 3-coordinate F− anions.[6]

Coordination geometry in magnesium fluoride[7]
Magnesium coordination Fluorine coordination

In the gas phase, monomeric MgF2 molecules adopt a linear molecular geometry.[4][5]

Uses

Optics

Magnesium fluoride is transparent over an extremely wide range of wavelengths. Windows, lenses, and prisms made of this material can be used over the entire range of wavelengths from 0.120 μm (vacuum ultraviolet) to 8.0 μm (infrared). High-quality, synthetic magnesium fluoride is one of two materials (the other being lithium fluoride) that will transmit in the vacuum ultraviolet range at 121 nm (Lyman alpha). Lower-grade magnesium fluoride is inferior to calcium fluoride in the infrared range.

Magnesium fluoride is tough and polishes well but is slightly birefringent and should therefore be cut with the optic axis perpendicular to the plane of the window or lens.[6] Due to its suitable refractive index of 1.37, magnesium fluoride is commonly applied in thin layers to the surfaces of optical elements as an inexpensive anti-reflective coating. Its Verdet constant is 0.00810 arcmin⋅G–1⋅cm–1 at 632.8 nm.[8]

Safety

Chronic exposure to magnesium fluoride may affect the skeleton, kidneys, central nervous system, respiratory system, eyes and skin, and may cause or aggravate attacks of asthma.[9]

References
  1. W.M. Haynes, ed. (2016), "Physical Constants of Inorganic Compounds", Handbook of Chemistry and Physics (97th ed.), CRC Press, p. 4–71 (789), ISBN 978-1-4987-5429-3
  2. "Magnesium Fluoride Material Safety Data Sheet". Science Labs. May 21, 2013. Retrieved October 13, 2017.
  3. "Magnesium fluoride". CAS DataBase List. ChemicalBook. Retrieved October 13, 2017.
  4. Wells, A. F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford University Press. pp. 413, 441. ISBN 978-0-19-965763-6.
  5. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 117–119. ISBN 978-0-08-037941-8.
  6. Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.
  7. Haines, J.; Léger, J. M.; Gorelli, F.; Klug, D. D.; Tse, J. S.; Li, Z. Q. (2001). "X-ray diffraction and theoretical studies of the high-pressure structures and phase transitions in magnesium fluoride". Phys. Rev. B. 64 (13): 134110. Bibcode:2001PhRvB..64m4110H. doi:10.1103/PhysRevB.64.134110.
  8. J. Chem. Soc., Faraday Trans., 1996, 92, 2753 - 2757. doi:10.1039/FT9969202753
  9. "Magnesium Fluoride Material Safety Data Sheet". ESPI Metals. August 2004. Archived from the original on 2017-10-28. Retrieved October 13, 2017.
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