Dynamic Property of H2O in Layered VOPO4·2H2O Studied by Solid-State NMR

The dynamics of interlayer H 2 O in VOPO 4 ·2H 2 O have been studied by 1 H and 2 H NMR measurements. This compound contains two different kinds of water molecules. One of the two water molecules has a coordination bond to the V in the layer. The 2 H NMR spectrum at 150 K was reproduced by one component with the quadrupole-coupling constant QCC = 220kHz and the asymmetry parameter η = 0.12. This result suggests that all H 2 O molecules are static at this temperature. In the temperature range of 160-240 K, both interlayer H 2 O molecules show 180°-flipping motion from the 2 H NMR spectra. This motion of the two different H 2 O molecules suggests the hydrogen-bonding network between these interlayer H 2 O. The activation energies of this motion could be determined to be 30 kJ mol -1 from the 2 H NMR spectrum simulation. Additionally, the diffusional component also appeared above 240 K. Above 270 K, two-dimensional diffusion of the interlayer species is suggested in this material.