NMR INVESTIGATION ON MOLECULAR MOBILITY OF PYRAZOLE AND PYRIDAZINE INTERCALATED IN LAYERED ALPHA-ZIRCONIUM PHOSPHATE

Intercalation compounds of alpha-zirconium phosphate with pyrazole and pyridazine have been investigated by solid state NMR measurements, in order to have information about the proton conduction mechanism. C-13 chemical shifts, obtained under CP MAS conditions, show that both het erocycle guest molecules are in the protonated state, at least partial ly. Proton spin-spin relaxation experiments have been carried out in t he temperature range 200-400 K. At 273 K no molecular motions occur in either sample on the measurement time scale. With increasing temperat ure, a narrow component appears in the free induction decay of the pyr azole intercalate, which can be assigned to proton containing fragment s involved in translational diffusion. This component is absent when a ll the mobile acidic protons are substituted by deuterons; this exclud es translational mobility of the guest molecules and supports the Grot thus type mechanism previously proposed. No significant changes are ob served in the free induction decay of the pyridazine intercalate with increasing temperature, thus indicating hindered rotation up to 350 K. These interpretations agree with the results obtained for both interc alation compounds from spin-lattice relaxation experiments in the temp erature range 150-350 K.