P-31 MAS-NMR study of R ' R-x '' yP6O19.nH(2)O cyclohexaphosphates

Several alkali/alkaline-earth Rx+Ry2+P6O18.nH(2)O cyclohexaphosphates, with R+=Li, Na, K, Cs, NH4, T1, DBA; R2+=Ca, Zn, Cd, have been analyzed by P-31 MAS-NMR spectroscopy. From their NMR spectra, the number and the multiplic ity of crystallographic sites have been analyzed and compared with those de duced by symmetry considerations from X-ray diffraction data. A linear depe ndence of the isotropic chemical shift values of NMR components on the POP angles of cycles has been obtained. However, some influence of the charge a nd polarizing strength of alkali and alkaline-earth cations has also been d etected. Finally, principal values of the chemical shift tensor of P atoms have been analysed in terms of local symmetry and tetrahedral ring distorti ons. (C) 2001 Elsevier Science B.V. All rights reserved.