PO43- tetrahedra in SbPO4 and SbOPO4:: a 31P NMR and XPS study

Crystalline SbPO4 and SbOPO4 have been investigated by using NMR, XPS and IR techniques to understand the changes in the electronic characteristics of phosphorus in PO43- tetrahedra. The observed values of P-31 chemical shift for SbPO4 and SbOPO4, are found to be -18 and -31.8 ppm, respectively, indicating that P-31 nuclei are more shielded in SbOPO4. The binding energy values for 2p electrons of phosphorus in SbPO4 and SbOPO4 are 133.9 and 137.8 eV, respectively, suggesting that the electron density around phosphorus is less for SbOPO4. These two apparently contradictory inferences have been explained by considering the decreased paramagnetic contribution to the P-31 chemical shift values brought about by the decreased electron density around oxygen atoms present in P-O-Sb5+ linkages as compared to that of P-O-Sb3- linkages. Oxygen is XPS and IR studies of these samples provide direct evidence in support of these explanations. (C) 2002 Elsevier Science B.V. All rights reserved.