Electron-transferreactions between iron and cobalt complexes were studied in β-cyclodextrin (βCD), 2-hydroxypropyl-β-cyclodextrin (HβCD), and 18-crown-6 ether (18C6) solutions. The results were rationalized taking as the basis the Marcus−Hush formalism. We employed two different approaches, depending on the kind of receptor and solvent, to obtain the reorganization and reactionfreeenergies that