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

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.