A family of rare earth complexes with chelating furan biradicals: syntheses, structures and magnetic properties

Abstract

The combination of anisotropic Ln^III ions and the furan biradical results in six complexes, namely, [Ln(hfac)₃(NITFumbis)]₂ (Ln = La(1), Ce(2), Pr(3), Gd(4), Tb(5), Dy(6); hfac = hexafluoroacetylacetone; NITFumbis = (2,5-bis-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)furan). Compounds 1–3 are isostructural and crystallize in the P space group, while compounds 4–6 crystallize in the P2₁/c space group. For all the six complexes, the coordination number around the lanthanide ion is eight, and the polyhedron is in a distorted 4,4-bicappped trigonal prism or triangular dodecahedron coordination geometry (D_2d or C_2v symmetry) finished by three bischelate hfac⁻ ligands and one bidentate radical ligand. DC magnetic studies show that the Ln(III) ions interact antiferromagnetically with the directly bonding nitronyl nitroxide radicals in all the six complexes. Especially, for complex 4, an intramolecular antiferromagnetic interaction between the two radicals is observed with the largest J (J_Rad–Rad = −24.89 cm⁻¹) ever reported in Ln(III)-radical systems, and at low temperature, intermolecular ferromagnetic interaction also plays an important role. In addition, complex 6 exhibits field-induced single-molecule magnet (SMM) behavior.