Magnesium fluoride
Magnesium fluoride is an ionically bonded inorganic compound with the formula. The compound is a colorless to white crystalline salt that is transparent over a wide range of wavelengths, such that it is used in the optical windows of space telescopes. It occurs naturally as the rare mineral sellaite.
Production
is prepared from magnesium oxide with sources of hydrogen fluoride such as ammonium bifluoride, by the breakdown of it:Related metathesis reactions are also feasible:
Structure
The compound crystallizes as tetragonal birefringent crystals. The structure of the magnesium fluoride is similar to that of rutile, featuring octahedral cations and 3-coordinate fluoride| anions.| Magnesium coordination | Fluorine coordination |
In the gas phase, monomeric molecules adopt a linear molecular geometry.
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 to 8.0 μm. High-quality, synthetic magnesium fluoride is one of two materials that will transmit in the vacuum ultraviolet range at 121 nm.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. 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 0.00810arcmin⋅G−1⋅cm−1 at 632.8 nm.