Insight into Mechanism by Analytical Methods

Different spectroscopic, microscopic and diffraction methods like IR and Raman spectroscopy, TEM or XRD were applied to characterize educts, intermediates or products of the sol-gel process. For a detailed insight into the mechanism of the fluorolytic sol-gel process, however, the application of NMR spectroscopy is the method of choice. The NMR experiments, both in liquid and in solid state, allow direct observations of local structures and their changes even if the matrices suffer from a loss of lattice periodicity. For the fluorolytic so-gel process both liquid state NMR experiments were realized for the alkoxide solutions, sols and thin gels as well as solid state MAS NMR experiments for the alkoxide, dried alkoxide fluoride gels and high-surface fluorides including H, 

First NMR studies on possible structures of Al(OiPr)3 in different solutions range back to 1963 [18] followed by first Al NMR measurements in 1973 [19]. Since that 

2 Structural Changes at the Fluorination Process in Sols and Thin Gels 

Isolated single crystals and their structures only give an idea of very early steps of fluorination, producible only with an understoichiometric fluorine supply. Changes in the local aluminium and fluorine coordination in solutions, sols and thin gels are 

Moving to the third stage, a more and more stable network is formed with A1 F ratios equal to 1 2 and 1 3. The amount and spread of fourfold and fivefold coordinated Al-species decreases, ending up with sixfold AlFx(0 Pr)6 x species (x = 4 and 5) as deduced from the chemical shift correlation graphs [26—28, 36, 37]. 

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