A Stable Radical-Substituted Radical Cation with Strongly Ferromagnetic Interaction: Nitronyl Nitroxide-Substituted 5,10-Diphenyl-5,10-dihydrophenazine Radical Cation

摘要

Recently, the magnetic properties of organic compounds have attracted a great deal of attention. Various approaches toward organic magnetic materials have been taken, both theoretically and experimentally. Of these, an approach with a radical-substituted radical ion as a spin building block is particularly interesting. Yamaguchi and co-workers theoretically explored organic ferro- and ferrimagnets with various patterns of radical-substituted donor-acceptor charge transfer (CT) complexes. Although the related experimental studies have been examined using aniline-, ferrocene-, and TTF-frameworks as basic structures of CT-complexes, paramagnetic behavior has been observed in most cases and the expected ferro- or ferrimagnetic properties have not been observed. In general, spins on donors and acceptors in usual CT-complexes have large intermolecular antiferromagnetic interactions ranging between -100 and -1000 K. To realize the expected properties, a comparably large intramolecular J (half the singlet-triplet energy gap ΔE_(ST)) between the radical and radical ion moieties should therefore be essential. In this context, the thianthrene-based radical cations recently reported by Sugawara and co-workers seem to be attractive, although the J values of these spectroscopically detected species have not been determined because of their instability. The development of a molecular system with isolable stability and a large J is extremely important in the construction of molecular magnets. Dihydrophenazines are superior electron donors, giving highly stable radical cations that have large spin densities on the nitrogen and the C2 carbon atoms. We report the synthesis, structure, and magnetic properties of a nitronyl nitroxide-substituted 5,10-diphenyl-5,10-dihydrophenazine radical cation (1~+).