Influence of Protonation and Iron(II) Complexation on Magnetic Interactions in Spin‐Labeled Mechanically Interlocked Molecules

This study reports the effects of protonation and Fe(II) complexation on the exchange coupling and magnetic properties of a [2]-rotaxane and its corresponding free-axle biradicals. The rotaxane features nitronyl-nitroxide units as bulky stopper groups, a triazole-pyridine-triazole ligand as the axle component, and a bipyridine moiety within the macrocyclic ring. Our findings, obtained by Electron Paramagnetic Resonance spectroscopy in solution and magnetometry in solid state, demonstrate that rotaxanation and protonation induce profound changes in the magnetic interactions of the biradical both in its free form and as complexed with Fe(II). These results highlight the transformative impact of the mechanical bond on the electronic structure of interlocked radical systems.