31 P nuclear magnetic resonance investigation of solid dodecatungstophosphoric acid H 3 PW 12 O 40 ·xH 2 O at different hydration levels

The NMR linewidths and the T1 relaxation time of 31P in solid dodecatungstophosphoric acid at different hydration levels have been measured at room temperature, both in systems containing H2O and in systems where H2O was partially substituted by D2O. These data have been analysed in terms of relaxation contributions due to mechanisms such as the dipolar interaction of 31P with active tungsten nuclei and protons. Analysis of the experimental data indicates that polyanions do not rotate in the crystal lattice and that protons can penetrate into the Keggin cage.