Theoretical studies on contributions of SOMO–SOMO and other couplings to the magnetic interaction in radical clusters

The origin of intermolecular magnetic interactions of benzyl radical dimers (BRDs), which are key models of molecule-based magnetic materials, has been investigated by complete active space (CAS) SCF calculations. Effective exchange integrals (J-values) were obtained in combination with Heisenberg model. The results have been discussed on the basis of the extended McConnell (EM) model proposed by us. For the face-to-face stacking BRD, the J-value was negative, indicating anti-ferromagnetic interaction, because of the SOMO–SOMO overlap (OO) effect. On the other hand, J-value showed the ferromagnetic interaction for the para-stacking mode, because of the spin polarization (SP) plus electron correlation (EC). The CASSCF results are wholly consistent with the EM model.