Magnetic relaxation in mononuclear Tb and Dy complexes involving chelate nitronyl nitroxide ligand

Three new lanthanide-nitronyl nitroxide radical complexes [Ln(tfac) 3 (NIT-2thz)] (Ln(III) = Gd 1, Tb 2, Dy 3; tfac = trifluoroacetylacetonate; NIT-2thz = 2-(2′-thiazolyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized. Single crystal X-ray diffraction analyses reveal that complexes 1 – 3 are isomorphous. They all crystallized in the C2/ c space groups. Each central Ln(III) ion is eight-coordinated by three bischelate tfac ligands and one radical ligand. More specifically, NIT-2thz acts as a chelate ligand to link one Ln(III) ion through its nitrogen atom of the thiazole ring and oxygen atom of the N–O group to form a two-spin system. Magnetic studies show that Gd complex exhibits ferromagnetic Gd(III)–radical coupling, Tb and Dy complexes exhibit frequency-dependent out-of-phase signals.