Sol–gel-fluorination synthesis of amorphous magnesium fluoride

The sol–gel fluorination process is discussed for the reaction of magnesium alkoxides with HF in non-aqueous solvents to give X-ray amorphous nano-sized magnesium fluoride with high surface areas in the range of 150–350 m2/g (HS-MgF2). The H2 type hysteresis of nitrogen adsorption–desorption BET-isotherms is indicative for mesoporous solids. A highly distorted structure causes quite high Lewis acidity, shown by NH3 temperature-programmed desorption (NH3-TPD) and catalytic test reactions. XPS data of amorphous and conventionally crystalline MgF2 are compared, both show octahedral coordination at the metal site. Thermal analysis, F-MAS NMR- and IR-spectroscopy give information on composition and structure of the precursor intermediate as well as of the final metal fluoride. The preparation of complex fluorides, M+MgF3−, by the sol–gel route is reported. From the magnesium fluoride gel of the above process thin films for optical application are obtained by, e.g., spin coating.