Three new mononuclear tri-spin lanthanide-nitronyl nitroxide radical compounds: syntheses, structures and magnetic properties

Based on the nitronyl nitroxide radical, 2-(4-(methoxycarbonyl)phenyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (1, NITPhCOOMe), and three mononuclear tri-spin compounds [Ln(hfac)(3)(NITPhCOOMe)(2)] (Ln = Gd (2), Tb (3), Dy (4); hfac = hexafluoroacetylacetonate) are successfully synthesized and fully characterized. Compounds 2 and 4 are isostructural and crystallize in the C2/c space group, while compound 3 crystallizes in the P2(1)/c space group. For compounds 2-4, the central metal ions are all eight-coordinate in distorted triangular dodecahedral LnO(8) coordination geometry (D-2d symmetry) completed by three bischelate hfac(-) ligands and two monodentate radicals. Magnetic studies show that radical 1 undertakes the transition from the paramagnetic state to 3D antiferromagnetic ordering at 4.2 K. In addition, compound 3 exhibits field-induced single-molecule magnet (SMM) behavior.