Hochfeld-27Al-NMR-Untersuchungen zur Aluminiumkoordination in kristallinen Aluminiumphosphaten

High-field ²⁷Al-NMR Investigations on the Aluminium Coordination in Crystalline Aluminium Phosphates The ²⁷Al NMR spectra of crystalline aluminium phosphates obtained at high-magnetic fields under magic-angle spinning (MAS) conditions allow a direct determination of the aluminium coordination. So for five new Al phosphates it is shown that, as it is almost exclusively the case for Al phosphates of known structures, the Al is octahedrally coordinated, too. Chemical shifts between ?13 and ?21 ppm for isolated AlO₆ octahedra, and 39 ppm for isolated AlO₄ tetrahedra (in crystalline AlPO₄), were determined. In comparison to the results on aluminates and aluminum oxides these values are generally upfield-shifted about 30 ppm. The stronger magnetic shielding is attributed to the influence of the phosphorus atoms present in the second coordination sphere of the aluminum.