High-spin Polycarbenes as Models for Organic Ferromagnets

Abstract

In response to the Mataga's prediction of ferromagnetic hydrocarbons (1968), we have taken up the study of two series of high-spin polycarbenes (1 and 2). The corresponding polydiazo compounds were prepared through a series of unambiguous synthetic reactions and photolyzed in 2-methyltetrahydrofuran matrices and in single crystals of a benzophenone host at cryogenic temperatures. The ESR fine structures and magnetic susceptibilities were measured and analyzed to show that the highest spin states were generated as the electronic ground state of 1 and 2. Similarly, isomeric bis(diazo)-[2.2]paracyclophanes were prepared añd photolyzed to find, in good agreement with the McConnell's theory on the ferromagnetic intermolecular interaction between organic free radicals (1963), that the pseudoortho and pseudopara dicarbenes have the ground quintet state while the pseudometa isomer is in the ground singlet state. A strategy for increasing the spin ordering over the high-spin aromatic molecules by orienting the stacking mode was thus obtained. Relevance of these results to macroscopic ferromagnets is discussed. © 1986 IUPAC