Ethylene has been established to form stable π-complexes with Ag+ cations in Ag-modified zeolite H-ZSM-5 (Ag/H-ZSM-5), which strongly affect the reactivity of ethylene on this catalyst. With the aim of revealing the catalytic and adsorptive properties of Ag+ cations in Ag/H-ZSM-5, a characterization of the mobility of ethylene π-complex, located in the zeolite pores, has been performed with 2H solid-state NMR spectroscopy. Ethylene molecules were established to remain bound to the Ag+ cations at temperatures up to 556 K. In the bound state, ethylene exhibits a 2H NMR line shape typical for anisotropic motions. It is inferred that being adsorbed on Ag+ cation, ethylene molecule is involved in two internal rotations about its symmetry axes: along the C2 axis aligned with the C═C bond and about the second C2′ axis orthogonal to the molecule plane. The first rotation occurs with the rate k1 of 10–40 kHz and activation barrier E1 = 2.3 kJ mol–1, while the second motion occurs with the rate k2 of 10–400 kHz and...