Magnetic Interaction Observed in Hetero Biradical Derivatives Containing a 2,2,5,5-Tetramethylpyrrolin-1-yloxyl Unit as a Localized Spin Center.

The magneto-structural correlation of hetero biradical derivatives containing a 2,2,5,5-tetramethylpyrrolin-1-yloxyl unit as a localized spin center and a verdazyl or nitronyl nitroxide radical is reported. The magnetic susceptibility measurement revealed that the verdazyl attached biradical 1 exhibits ferromagnetic interaction, whereas antiferromagnetic interaction is observed for nitronyl nitroxide attached biradical 2. An EPR study in toluene glass matrix suggests that both 1 and 2 have a ground triplet state. DFT calculations predict that there is intramolecular ferromagnetic interaction for both biradicals. The computation also suggests that the intramolecular magnetic interaction is weaker with larger dihedral angle between pyrroline ring and verdazyl ring/O-N-C-N-O plane of nitronyl nitroxide. The computations of model compounds 3 and 4 suggest that spin polarization on vinylic moiety without distribution of SOMO might be an essential condition for the intramolecular ferromagnetic interaction.