A slowly magnetic relaxing Sm^III monomer with a D_5h equatorial compressed ligand field

By using a bi-dentate phosphine oxide ligand L (L = bis(diphenylphosphino)methane dioxide), two mono-nuclear lanthanide complexes [LnL(2)(DMF)Cl-2]Cl (Ln = Sm,1; Dy,2) with aD(5h)equatorial ligand field (LF) are obtained.Ab initioCASSCF calculations suggest that the equatorial LF promotes the magnetic anisotropy of the central Sm(III)and impair that of Dy-III. Alternating current (ac) susceptibility measurements reveal that the samarium complex is the first Sm(III)mono-nuclear complex with slow magnetic relaxation. The isostructural Dy(III)compound, in contrast, relaxes much faster. Further magnetic property studies were then performed to probe the origin of magnetic anisotropy and magnetic relaxations.