Solid-state aluminium-27 nuclear magnetic resonance chemical shift and quadrupole coupling data for condensed AlO4 tetrahedra

Abstract

Aluminium-27 n.m.r. isotropic chemical shifts and quadrupole coupling data for AlO₄ tetrahedra in polycrystalline aluminates and aluminate hydrates with various degrees of anion condensation and with different cations have been studied. It is shown that the various types of condensed AlO₄ tetrahedra differ in size and symmetry of the electric field gradient tensor at the Al site, but not in the ²⁷Al chemical shift. A slight variation in the chemical shift values of entirely connected AlO₄ tetrahedra around 80 p.p.m. indicates weak cation effects and other structural influences. A markedly increased Al shielding, however, was observed for tetrahedra with lengthened Al–O distances which occur in AlO₄ tetrahedra with neighbouring AlO₆ octahedra.