Crystalline aluminium hydroxy fluorides—Suitable reference compounds for 19F chemical shift trend analysis of related amorphous solids

On the basis of MAS NMR-data for crystalline AlFx(OH)3−x·H2O samples in the pyrochlore structure, 19F chemical shifts correlate with the average chemical composition of the octahedral environment, given by AlFxO6−x in these compounds. tribution of local structures in sol–gel derived amorphous AlFx(OX)3−x·XOH (X = H, R (alkyl)) compounds is of special interest as these or consecutively prepared solids exhibit remarkable features, for example, a high surface (HS) area accompanied by a high Lewis acidity. nsferring this scale of a 19F chemical shift trend analysis to such compounds a prediction of the chemical nature of the average Al coordination becomes possible. synthetic approach to crystalline aluminium hydroxy fluorides involving a sol gel fluorination as the first reaction step and an aluminium alkoxide as precursor compound is presented. Varying the amount of HF leads to different F–OH-ratios in the AlFx(OH)3−x compounds.