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Keywords:

  • Radicals;
  • Magnetic properties;
  • Single-molecule magnets;
  • Nitronyl nitrox­ides;
  • Lanthanides

Abstract

Four complexes based on rare earth biradicals [Ln(hfac)3(NITPhmbis)2]2 {Ln = La (1), Nd (2), Gd (3), Tb (4); hfac = hexafluoroacetylacetone; NITPhmbis = [1,3-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene]} were successfully synthesized under appropriate conditions. Single-crystal structures show that 1 is a mononuclear two spin complex and 24 are mononuclear three spin complexes, in which a NITPhmbis molecule acts as a bidentate ligand with one coordinated lanthanide ion. The four complexes are isomorphous, the coordination number around the lanthanide ion is eight, and the polyhedron is a 4,4-bicappped trigonal prism. For lanthanum(III) complex 1, the temperature dependence of the magnetic susceptibility indicates that weakly antiferromagnetically coupled radicals exist (Jrad–rad = –1.2 cm–1). In the case of neodymium(III) complex 2, its magnetic behavior gives antiferromagnetic NdIII–radical interactions, whereas for complexes 3 and 4, static magnetic properties show that the GdIII and TbIII ions interact ferromagnetically with the radical. The dynamic magnetic properties of 4 were also measured, and 4 was found to exhibit slow relaxation of the magnetization at low temperature.