Local Structural Changes at the Formation of Fluoride Sols and Gels: A Mechanistic Study by Multinuclear NMR Spectroscopy

A multinuclear NMR study using 27Al, 19F, 13C, and 1H as spin probes was performed (i) to address local structures in solutions of Al(OiPr)3 in isopropanol and (ii) to monitor the fluorination process passing sols and ending up with wet fluoride gels. On the basis of these findings, a possible reaction pathway could be derived for the sol−gel fluorination process: the first step of the synthesis of X-ray amorphous "high surface" (HS) AlF3. The mechanistic studies performed here give for the first time insights into the formation and changes of local structures of aluminum alkoxide fluoride sols and gels as necessary precursors for the new amorphous fluoride materials.