Pentahedral and Tetrahedral Aluminium Fluoride Species

6 Nanostructured Aluminium Hydroxyfluorides and Aluminium Fluoride Hydrate with Cationic Vacancies 

7 Siso Scale for Al and in Octahedral Aluminium Environments with Hydroxyl and Fluorine in the First Coordination Sphere 

Following the studies mentioned above, pyrochlore AlFx(OH)3 x H2O with variable F-content was investigated by F MAS NMR and Al NMR at different magnetic fields up to 21.1 T, by Konig et al. [104,105]. In AlFg x(OH)x species Al iso increases nearly linearly with x (the studied samples are too numerous to be reported in Table 5.1) [105]. The F MAS NMR experiments show that F iso increases also nearly linearly with x for the same species [102]. Dehydration of the samples revealed the influence of the water molecules on F iso [104] and allows determining trend analysis for F in proton-poor substances. 

To conclude this section, we would like to indicate that Al, A1 and A1 coordination are easily discriminated due to their different Al chemical shifts. Moreover for crystallized disordered compounds with homogeneous composition and known structure, high field NMR experiments allow differentiating species with the same coordination number. On the contrary, for fluorinated aluminas and zeolithes and amorphous compounds, despite proximities between and Al clearly revealed by correlation experiments, the differentiation of such species remains difficult. 

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