31P, 1H NMR Relaxation and Molecular Mobility in Layered α-Zirconium Phosphate: Variable-Temperature NMR Experiments

Internal rotations in HPO4- groups and proton transfer between them have been characterized in static alpha-zirconium phosphate by variable-temperature measurements of P-31 T-1 and H-1 T-1 rho times. The H-1 T-1 rho times have been obtained by the kinetic of phosphorus proton cross polarization treated with the model. The calculations of the temperature T-1 relaxation dependences have resulted in the rotational activation energy of 2.6 kcal/mol (or 3.9 kcal/mol in account for the tau(C) distribution) and the proton transfer activation energy of 5.5 kcal/mol. Thus, two types of motions have been found in a-zirconium phosphate: the low-frequency proton transfer with the correlation time of 1.5 X 10(-5) s at 295 K and the high-frequency rotation in P-OH groups with the correlation time tau(c), of 2.2 X 10(-8) s at 295 K.