Effective exchange integrals and chemical indices for a phenalenyl radical dimeric pair

UHF, spin-polarized DFT, and CASSCF calculations have been performed for a 2,5,8-tri-t-butylphenalenyl radical dimeric pair and its simplified model to elucidate the characteristics of chemical bonding and the origin of strong antiferromagnetic coupling. The results show that the SOMO–SOMO overlap interaction is responsible for the strong antiferromagnetic interaction and intermediate covalent-bonding between the phenalenyl radicals. The t-butyl groups in the three β-positions hardly affect the magnetic coupling, simply playing steric hindrances in a crystalline state. Chemical indices can explain the bonding character and the efficiency of the electron correlation for the dimeric pair.