Tris-pyridylmethylamine (TPMA) complexes functionalized with persistent nitronyl nitroxide organic radicals

Abstract

The chance to have persistent organic radicals in combination with metals has attracted much interest since it offers the possibility of having new functional molecules with multiple open-shell elements. In this study, we report the synthesis of two tripodal tris(2-pyridyl)methylamine ligands (TPMA) functionalized with nitronyl nitroxide persistent radicals. The newly formed ligands have been used to coordinate zinc(II), copper(II), iron(II) and cobalt(II). The resulting complexes have been investigated by means of electron paramagnetic resonance (EPR), ESI-MS, FT-IR spectroscopy and X-ray diffraction. An electron reduction of the N–O radical moiety has been observed, depending on the metal used for the formation of the complex and the reaction conditions. We have observed small differences in the EPR spectra depending on the meta or para position of the radical moiety in the complex structure and some antiferromagnetic interactions between the paramagnetic M(II) ions and the radical species.