31P nuclear magnetic resonance investigation of solid dodecatungstophosphoric acid H3PW12O40·xH2O at different hydration levels

Abstract

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.