Single-molecule magnets based on rare earth complexes with chelating benzimidazole-substituted nitronyl nitroxide radicals

Abstract

Three rare earth–nitronyl nitroxide radical complexes [Ln(tfa)₃(NIT-BzImH)] (Ln(III) = Gd 1, Tb 2, Dy 3; tfa = trifluoroacetylacetonate; NIT-BzImH = 2-(2′-benzimidazolyl)-4,4,5,5-tetramethylimidazolyl-1-oxyl-3-oxide) have been successfully prepared and structurally characterized. X-Ray crystallographic analysis reveals that all three complexes are isomorphous. Their crystal structures consist of mononuclear molecule units in which lanthanide(III) is 8-coordinated to one NIT-BzImH and three trifluoroacetylacetonate ligands. The NIT-BzImH acts as a bidentate ligand via its nitrogen atom of the imidazole ring and the oxygen atom of the N–O group. The magnetic properties of complexes 1–3 were studied. All the three complexes exhibit ferromagnetic Ln(III)–radical coupling. AC magnetic susceptibility studies of 2 and 3 show slow magnetic relaxation suggesting that they behave as SMMs.