Comparative structural investigation of aluminium fluoride solvates

To get some insight by conclusions of analogy into the drying process of alcoholic aluminium fluoride sol–gels [AlF3/(ROH)x], the structures of α- and β-AlF3⋅3H2O as well as of the nonahydrate AlF3⋅9H2O are reinvestigated and discussed based on X-ray single crystal structural data. In addition, neutron diffraction experiments of the latter allowed the refinement of proton positions. In accordance with crystal structures, low-temperature solid state 27Al-, 1H- and 19F-MAS NMR spectra convincingly confirm the structural similarity between α-AlF3⋅3H2O and AlF3⋅9H2O, while the β-phase material is structurally different forming chain structures. Thermal analysis of AlF3/(ROH)x gave evidence for discrete AlF3:ROH ratios of only 1:0.45 and 1:0.1, and solution NMR showed some similarities between aqueous and alcoholic systems.

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