Nitronyl and imino nitroxide free radicals as precursors of magnetic phthalocyanine and porphyrin building blocks

Abstract

Phthalonitrile and benzaldehyde bearing α-nitronyl and α-imino nitroxide free radicals have been synthesized as precursors of nitroxide substituted phthalocyanine and porphyrin macrocycles. To ascertain the structure and radical type they have been characterized by single crystal X-ray crystallography and by electron paramagnetic resonance spectroscopy (EPR). Their EPR spectra coincide with those reported for previous nitroxides and are in good agreement with literature. Electrospray ionization mass spectroscopy (ESI) was used as a complementary and an alternative technique. Depending on the nature of the radical, two ionization behaviors have been underscored; imino radicals were detected as the [MH₂]⁺ cation ions and nitroxide radicals were detected as the [MH]⁺˙ radical cations. This differentiation is pointed out as an efficient and rapid method for preliminary characterization of the radical moieties and a judicious technique that allows the prompt detection of radicals at low concentration and straightforward confirmation of the structure.