Simple but useful scheme toward understanding of intramolecular magnetic interactions: Benzene-bridged oxoverdazyl diradicals

It has recently been shown that the types of intramolecular magnetic interactions of diradical systems can be changed by the types of radical group: syn-group (or α-group) and anti-group (or β-group). The aim of this study is to establish a useful scheme to understand and explain the intramolecular magnetic interactions in diradical systems regardless of radical groups and the topology of a coupler. We investigated the intramolecular magnetic coupling constant (J) of six oxoverdazyl diradicals (i-vi) coupled with a benzene ring based on the unrestricted DFT calculations. On the basis of our results, we devised a simple but useful scheme by combining the spin alternation rule and the concept of radical group classification. Consequently, it was found that the calculated J values and plots of spin density distributions were consistent with our proposed scheme. In addition, we discussed the closed-shell singlet (CS) state and the dihedral angle effect on J values in detail to comprehensively understand the magnetic interactions of diradical systems. Our scheme can provide the basic framework to design future organic high-spin molecules and organic magnetic materials.