Über basische Aluminiumsalze und ihre Lösungen. XI. Vergleichende 27Al-NMR-Untersuchungen am Mineral Zunyit und basischen Aluminium-Salzen mit tridekameren Al-oxo-hydroxo-aquo-Kationen

Basic Aluminium Salts and their Solutions. XI. ²⁷Al-NMR Studies Comparing the Mineral Zunyite and Basic Aluminium Salts of Tridecameric Al-oxo-hydroxo-aquo-Cations Solid-state high resolution ²⁷Al NMR studies of basic aluminum sulphate and the mineral zunyite, both containing tridecameric Al-oxo-hydroxo groups, show different ²⁷Al spectra. While for zunyite both AlO₆ octahedra (0 ppm) and the central AlO₄ tetrahedron (69 ppm) are observed in the spectrum, in the case of the basic aluminum sulphate only the tetrahedrally coordinated Al (59 ppm) is detected by NMR. This behaviour is explained by structural data, which indicate stronger distortions of the AlO₆ octahedra in the case of the basic aluminum sulphate. The increased shielding of the fourcoordinated Al of the basic sulphate is attributed to an increased ionic character of the Al? O bond in this compound.