Hyperfine anisotropy and mobility of organic radical cations in zeolites

Quantitative simulations of EPR powder spectra of organic radical cations in zeolites are reported. The anisotropy of the hypefine interactions and of the g-factor tensors is interpreted in terms of the mobility of the species. The radical cation formed by spontaneous oxidation of tetramethylethene in activated HZSM-5 is shown to rotate about the axis perpendicular to the molecular plane at room temperature, but it is immobile at 100 K. The radical cation derived from 2,5-dimethylhexa-1,5-diene in H-mordenite can execute only librational motion on a timescale of ca. 50 ns.