Imidazoline-nitroxide radicals, paramagnetic molecular building blocks fromagnetic structures

The synthesis, characterization and magnetic properties of new series of me tal complexes based on spin-labelled pyridine, bipyridine, terpyridine, pol yaza-macrocycles and calix[4]arene scaffolds have been described. Magneto-s tructural correlations revealed that the nature and the amplitude of the ma gnetic interactions strongly depend on the torsion angles between the radic al and the metallic centre. In the 6,6'-bis-NIT-2,2'-bipyridine/Cu2- case. the interaction is antiferromagnetic, with J approximate to -167 cm(-1), wh ile with Ni2+ a large range of ferromagnetic interactions is found, dependi ng on the geometry of the first coordination sphere [from 40 to 7 cm(-1)], NIT for a nitronyle-nitroxyde radical. The presence of a pyridine spacer be tween the NIT radical and the metallic centre (4'-NIT-2,2':6',6''-terpyridi ne case) notably mitigates the interaction, which remains antiferromagnetic in all cases (J approximate to -7 cm(-1) with Ni2+). In the podand bipyrid ine-ligand. one nitroxide arm is bound equatorially and the second arm is a xially coordinated to Cu2+. With the Ni2+ and Zn2+ cations, both radicals a re axially bounded. In all complexes, the bipyridine/aminomethyl fragment i s meridionally complexed to the metal centre. (C) 2001 Academie des science s / Editions scientifiques et medicales Elsevier SAS.