WATER-STRUCTURE AND DYNAMICS IN H3PW12O40.NH2O AND H3PMO12O40NH2O - A DEUTERIUM MAGNETIC-RESONANCE STUDY

2H NMR has been used to investigate the secondary water structures of H3PW12O40·rtD2O and H3PMo12O40·nD2O. In the case of H3PW12O40 water is not structured up to n≃ 6. At n ≃ 6 a cubic structure exists, and at a higher water content, two orthorhombic structures can exist, for which we found the cell axes ratios. These two structures are the only ones observed with high water content. The causes determining the formation of each one have not been investigated. In one case both structures have been formed in the same sample. We found that water is structured on planes, and its diffusion is fast compared to the NMR measurement time (τC < 10-5 s). Similar conclusions about water dynamics are found in H3PMo12O40·nD2O, but in this case water is not structured for n < 10. At higher water content 2H NMR spectra suggest the existence of a secondary water structure, which we were not able to identify. © 1990 American Chemical Society.