NMR investigation on molecular mobility of pyrazole and pyridazineintercalated in layered α-zirconium phosphate
Abstract Intercalation compounds of α-zirconium phosphate with pyrazole and pyridazine have been investigated by solid state NMR measurements, in order to have information about the proton conduction mechanism.13C chemical shifts, obtained under CP MAS conditions, show that both heterocycle guest molecules are in the protonated state, at least partially. Proton spin-spin relaxation experiments have been carried out in the temperature range 200–400 K. At 273 K no molecular motions occur in either sample on the measurement time scale. With increasing temperature, a narrow component appears in the free induction decay of the pyrazole intercalate, which can be assigned to proton containing fragments involved in translational diffusion. This component is absent when all the mobile acidic protons are substituted by deuterons; this excludes translational mobility of the guest molecules and supports the Grotthus type mechanism previously proposed. No significant changes are observed 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 intercalation compounds from spin-lattice relaxation experiments in the temperature range 150–350 K.