Magnetic coupling in bis-nitronylnitroxide radicals: The role of aromatic bridges

Configuration interaction calculations have been applied to the study of the magnetic coupling in bis-nitronyl nitroxide radicals with benzene bridges. Molecular orbitals obtained with different localization schemes have been considered in the generation of the CI space, with the aim of investigating the role played by the various fragments in the magnetic interaction. The aromatic bridge is found significant, while fragments outside the magnetic-bridge-magnetic moiety can be neglected. Using simplified model molecular species, an accurate analysis of the ferromagnetic/antiferromagnetic coupling in the meta and para diradicals is reported.