A Family of Homologous Heterospin Complexes Based on Lanthanides and Biradical Ligands

Four complexes based on rare earth biradicals [Ln(hfac) 3 (NITPh m bis) 2 ] 2 {Ln = La ( 1 ), Nd ( 2 ), Gd ( 3 ), Tb ( 4 ); hfac = hexafluoroacetylacetone; NITPh m bis = [1,3‐bis(1′‐oxyl‐3′‐oxido‐4′,4′,5′,5′‐tetramethyl‐4,5‐hydro‐1 H ‐imidazol‐2‐yl)benzene]} were successfully synthesized under appropriate conditions. Single‐crystal structures show that 1 is a mononuclear two spin complex and 2 – 4 are mononuclear three spin complexes, in which a NITPh m bis 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 ( J rad–rad = –1.2 cm –1 ). In the case of neodymium(III) complex 2 , its magnetic behavior gives antiferromagnetic Nd III –radical interactions, whereas for complexes 3 and 4 , static magnetic properties show that the Gd III and Tb III 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.