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.