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

Abstract

Abstract The dynamics of interlayer H2O in VOPO4·2H2O have been studied by 1H and 2H 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 2H NMR spectrum at 150 K was reproduced by one component with the quadrupole-coupling constant QCC = 220 kHz and the asymmetry parameter η = 0.12. This result suggests that all H2O molecules are static at this temperature. In the temperature range of 160–240 K, both interlayer H2O molecules show 180°-flipping motion from the 2H NMR spectra. This motion of the two different H2O molecules suggests the hydrogen-bonding network between these interlayer H2O. The activation energies of this motion could be determined to be 30 kJ mol−1 from the 2H 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.