NMR - Crystallographic studies of aluminophosphate AIPO4-40

International audienceIn the solid-state NMR of inorganic materials, double-resonance (or 1H triple-resonance) experiments often involve a half-integer quadrupolar nucleus that has the disadvantage of exhibiting second-order anisotropic broadening. However, the introduction of two-dimensional multiple-quantum magic-angle spinning (MQMAS) has been the source of a tremendous improvement in the solid-state NMR of half-integer quadrupolar nuclei. By correlating triple (or higher) quantum with observable single-quantum coherences, Frydman demonstrated that it is possible to remove the second-order quadrupolar interaction leading to high-resolution spectra. Taking advantage of the highly resolved dimension of the experiment, double-resonance schemes such as CP, REDOR, or HETCOR have been proposed to obtain a better insight into the connectivity of solids. The MQMAS method not only produces highly resolved 27Al NMR spectra, making easy the determination of the aluminum coordination, but also allows the extraction of additional parameters such as the quadrupolar coupling constants, the isotropic chemical shifts, and the access to the distribution of these parameters