P-31 MAGIC-ANGLE-TURNING NMR-STUDIES OF THE CHEMICAL AND ELECTRONIC NATURE OF PHOSPHORUS IN MAGNESIUM ALUMINOPHOSPHATE MGAPO-20

The chemical and electronic nature of the various phosphorus environme nts in the microporous magnesium aluminophosphate MgAPO-20 has been in vestigated by P-31 magic-angle-turning NMR. Although the P(4Al) unit i s highly symmetric, Mg incorporation into the lattice distorts this sy mmetry by altering the three P-31 shielding tensors unevenly and thus producing chemical shift anisotropy (CSA) patterns. The P(3Al, 1Mg) un it is close to axial symmetry whereas P(2Al, 2Mg) is highly asymmetric . The dramatic change in the electronic nature of phosphorus by magnes ium substitution correlates with the number of magnesium atoms adjacen t to phosphorus. These experimental findings not only reveal a wealth of information on the electronic nature of phosphorus in MgAPO-20 but also constitute strong evidence as to the magnesium incorporation into the AlPO-20 lattice. In like manner, this contribution may extend to a new strategy for the understanding of isomorphous substitutions in m icroporous materials.