Structures and magnetic properties of five lanthanide-radical complexes constructed by 8-methoxyquinoline substituted tridentate chelating nitronyl nitroxide radical

Highlights: • Five new Ln-radical complexes were synthesized and magnetically characterized. • Tb-radical and Dy-radical complexes show the weak slow magnetic relaxation behaviors. • Weak ferromagnetic interactions were estimated in Gd/Tb-radical complexes. • The antiferromagnetic interactions were existed in Dy/Ho/Er-Rad complexes. Five lanthanide complexes [Ln(hfac)₃(8-MeOTQ-2-NIT)] constructed by a tridentate chelating 8-methoxyquinoline substituted nitronyl nitroxide radical (Ln=Gd (1), Tb (2), Dy (3), Ho (4), Er (5), hfac=hexafluoroacetylacetonate, 8-MeOTQ-2-NIT=2-(8-methoxyquinoline)-4,4,5,5- tetra-methylimidazoline-1-oxyl-3-oxide) have been successfully synthesized and characterized. The five complexes have similar mononuclear two-spin structures with one Ln^III ion and one radical (Rad) in the molecules. And all Ln^Ⅲ ions are nine-coordinated in the geometry between mono-capped square antiprism (C_4v) and a trigonal bipyramidal (D_3h). Alternating current magnetic studies show that Tb and Dy complexes display frequency dependence of out of phase signals indicating the slow magnetic relaxation behavior of single molecular magnets. The ferromagnetic interactions in Gd/Tb-Rad complexes and the very weak antiferromagnetic interactions in Dy/Ho/Er-Rad complexes were estimated by the rough model combining lanthanide single ions approximation and molecular-field approximation.