2-(3- and 4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-N-oxide (abbreviated as m- and p-MPYNN), the butyl derivative (m- and p-BuPYNN), 4-(N-ethylammonium)-2,2,5,5-tetramethylpiperidin-1-oxyl (ETEP) and N,N,N′,N′-Tetramethyl-1,4-phenylenediamine radical cation (TMPD⁺) have been successfully intercalated into saponite clay. The amount of intercalated material has been determined via UV/VIS spectroscopy, elemental analysis and EPR spectroscopy, and the expansion of the layer distance from ∼12.0 to ca. 15 Å has been measured by X-ray powder diffraction. The magnetic properties of these materials, which result from the interplay of the modified intermolecular interactions between the guest species, and the additional interaction with the host lattice, have been characterized by magnetic susceptibility, EPR and solid state NMR measurements. While the ²⁹Si and ²⁷Al NMR spectra show little influence of the radical species on the local structural environments of the nuclei in the host lattice, the guest–host interaction manifests itself in significant line-broadening and (in some cases) resonance displacements of the ¹H NMR signals belonging to the molecular radical cations. In the case of TMPD⁺ intercalates, the NMR and EPR data indicate predominant radical dimerization within the interlayer space.