A. Philippou et al., P-31 MAGIC-ANGLE-TURNING NMR-STUDIES OF THE CHEMICAL AND ELECTRONIC NATURE OF PHOSPHORUS IN MAGNESIUM ALUMINOPHOSPHATE MGAPO-20, JOURNAL OF PHYSICAL CHEMISTRY B, 102(45), 1998, pp. 8974-8977
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.