Benzene-d and toluene-d as guest molecules in micropores of a layered zirconium phosphonate: H, C{ H}, and P{ H} solid-state NMR, deuterium NMR relaxation, and molecular motions.

For the first time, pore spaces in the Zr (IV) phosphonate (1) as a representative of layered metal (IV) phosphonate materials have been investigated by studying mobility of guest molecules, benzene-d , and toluene-d . Guest molecules located in micropores of 1 have been characterized by solid-state C{ H} and H NMR spectra in static samples with varying temperatures. At moderately low temperatures, the benzene and toluene molecules experience fast isotropic reorientations and show the motionally averaged liquid-like carbon and deuterium line shapes in the NMR spectra. At lower temperatures, two anisotropic motional modes have been found for benzene molecules by analyzing the H NMR line shapes: the well-known in-plane C rotation and composite motions. Interpretation of the variable-temperature H T relaxation times identifies the composite motions as 120° flips around the C axis perpendicular to the molecular plane and the rotations around the molecular para-C-C axis. The data obtained resulted in the idealized (cylinder-shaped) model of micropores in compound 1 with the diameter of 20-30 Å. Furthermore, the activation energy of 20.1 kJ/mol determined for the benzene motions classifies the molecule-surface interactions as weak but enough for absorption.