Dynamic behavior of acetonitrile molecules adsorbed in AlPO₄-5 and SAPO-5 studied by ¹H and ²H NMR

We studied dynamic behavior of acetonitrile molecules adsorbed in molecular sieves AIPO₄-5 and SAPO-5 by ¹H and ²H solid state NMR methods and compared the result with that in bulk acetonitrile. The isotropic rotation of molecules is observed in AIPO₄-5 above 200 K but they are bound to Brønsted acid sites on the wall in SAPO-5 even at room temperature. An anomalous frequency dependency of ¹H NMR T₁ observed in acetonitrile in SAPO-5 implies a large distribution of the environment around the molecules. This distribution of environment is attributable to the random arrangement in positions of acid sites and acetonitrile molecules. It was shown that molecules in AIPO₄-5 are movable compared with those in bulk although the interaction with the pore wall seems to hinder motions.