Elucidating structure and dynamics of crystalline alpha-zirconium phosphates intercalated with water and methanol by multinuclear solid-state MAS NMR: A comprehensive NMR approach

Solid-state NMR experiments on H-2, P-31, C-13, and H-1 nuclei, including P-31 T-1, H-1 T-1, and H-1 T-1 rho measurements, as well as on the kinetics of proton-phosphorus cross-polarization have been performed to characterize the crystalline and amorphous alpha-zirconium phosphates, which were intercalated with D2O and/or CD3OD. The C-13{H-1} CP MAS NMR experiment performed for compound 1-CD3OD (Zr (HPO4)(2)(.)0.2CD(3)OD) with carbon cross-polarization via protons of phosphate groups has provided a prove that the methanol was intercalated into the interlayer spaces of this compound. The variable-temperature H-2 solid-echo MAS NMR spectra of intercalated compounds demonstrated that the methanol molecules, in contrast to the mobile water, were immobile, keeping, however, free CD3 rotations around the C-3-axis. It has been demonstrated that the intercalated species, D2O and CD3OD, do not affect the high-frequency motions of the phosphate groups. By utilizing local structural models that satisfy the constraints of the experimental data, it has been suggested that the immobile methanol molecules are located in the cavity between two neighboring layers of the zirconium phosphates. Thus, the present work illustrates the reliable criteria in a comprehensive NMR approach to structural and dynamic studies of such systems.