Lanthanide Complexes with a Tripodal Nitroxyl Radical Showing Strong Magnetic Coupling

A series of isomorphous mononuclear complexes of Ln(III) ions comprising one stable tripoidal oxazolidine nitroxyl radical were obtained in acetonitrile media starting from nitrates. The compounds, [LnRad(NO₃)₃] (Ln = Gd, Tb, Dy, Tm, Y; Rad = 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl), have molecular structure. Their coordination polyhedron, LnO₇N₂, can be described as a tricapped trigonal prism with symmetry close to D_3h. The value of 23 cm^-1 for the antiferromagnetic coupling Gd-Rad established from the DC magnetic and EPR data is a record strength for the complexes of 4f-elements with nitroxyl radicals. The terbium derivative displays frequency-dependent out-of-phase signals in zero field indicating single-molecule magnetic behavior with an effective barrier of 57 cm^-1.