Di-tert-butyl nitroxide was adsorbed on LiY zeolites, and the formation of adsorption complexes of this radical with lithium cations was proven by means of two-dimensional electron spin-echo modulation spectroscopy. The evaluation of the experimental hyperfine sublevel correlation spectra revealed a negative isotropic hyperfine coupling for both lithium isotopes. Furthermore a complex geometry was obtained where the Li+ ion is located within the molecular mirror plane of the DTBN nitroxide radical with an oxygen-lithium cation bond length of 0.19 nm.