91Zr and 25Mg solid-state NMR characterization of the local environments of the metal centers in microporous materials

Solid-state NMR was used to examine the local environments around the metal centers in microporous zirconium silicates and an aluminophosphate incorporated with Mg. 91Zr and 25Mg Quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) spectra were obtained at different magnetic fields from which the quadrupolar and chemical shift parameters were extracted. The relationships between the NMR parameters and metal local structures were discussed. Theoretical calculations were performed on the model clusters. The work shows that using sensitivity enhancement techniques such as QCPMG and performing NMR experiments at the highest possible magnetic fields allow one to probe low-gamma, quadrupolar metal centres in microporous materials.