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 [AlF 3/(ROH) x ], the structures of α- and β-AlF 3⋅3H 2O as well as of the nonahydrate AlF 3⋅9H 2O 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-AlF 3⋅3H 2O and AlF 3⋅9H 2O, while the β-phase material is structurally different forming chain structures. Thermal analysis of AlF 3/(ROH) x gave evidence for discrete AlF 3:ROH ratios of only 1:0.45 and 1:0.1, and solution NMR showed some similarities between aqueous and alcoholic systems.