Magnesium fluoride

Magnesium fluoride

Names
Other names Sellaite Irtran-1
Identifiers
CAS Number	7783-40-6 Y
3D model (Jmol)	Interactive image
ChemSpider	22952 Y
ECHA InfoCard	100.029.086
EC Number	231-995-1
PubChem	24546
RTECS number	OM3325000
InChI InChI=1S/2FH.Mg/h2*1H;/q;;+2/p-2 Y Key: ORUIBWPALBXDOA-UHFFFAOYSA-L Y InChI=1/2FH.Mg/h2*1H;/q;;+2/p-2 Key: ORUIBWPALBXDOA-NUQVWONBAK
SMILES [Mg+2].[F-].[F-]
Properties
Chemical formula	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)
Solubility in water	0.013 g/100 mL
Solubility product (Ksp)	5.16·10−11
Solubility	Insoluble in ethanol
Magnetic susceptibility (χ)	−22.7·10−6 cm3/mol
Refractive index (nD)	1.37397
Structure
Crystal structure	Rutile (tetragonal), tP6
Space group	P42/mnm, No. 136
Thermochemistry
Specific heat capacity (C)	61.6 J·mol−1·K−1
Std molar entropy (So298)	57.2 J·mol−1·K−1
Std enthalpy of formation (ΔfHo298)	-1124.2 kJ·mol−1
Gibbs free energy (ΔfG˚)	-1071 kJ/mol
Hazards
R-phrases	R20, R22
NFPA 704	0 3 0
Lethal dose or concentration (LD, LC):
LD50 (median dose)	2330 (rat, oral)
Related compounds
Other anions	Magnesium chloride Magnesium bromide Magnesium iodide
Other cations	Beryllium fluoride Calcium fluoride Strontium fluoride Barium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

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

Related metathesis reactions are also feasible.

The compound crystallizes as tetragonal birefringent crystals. The structure of the compound is similar to that in rutile, featuring octahedral Mg²⁺ centers and 3-coordinate fluoride centres.

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 VUV grade MgF₂ is quite expensive, in the region of $3/kg (2007) but the real cost of optics in this material is due to relatively low volume manufacture. However, with lithium fluoride it is one of the two materials that will transmit in the vacuum ultraviolet range at 121 nm (Lyman alpha) and this is where it finds its application. Lower grade MgF₂ is sometimes used in the infrared but here it is inferior to calcium fluoride. MgF₂ is tough and works and polishes well, but it is slightly birefringent and should be cut with the optic axis perpendicular to the plane of the window or lens.