Effect of nuclearity and symmetry on the single-molecule magnets behavior of seven-coordinated β-diketonate Dy(III) complexes

A couple of mononuclear and dinuclear lanthanide complexes, Dy(thd)(3)(Py) (1), Ln(2)(thd)(6)(4,4'-Bpy) (Ln = Dy (2), Gd (3), Py = Pyridine, 4,4'-Bpy = 4,4'-Bipyridine) have been designed and isolated from the reaction of beta-diketonate-based ligand 2,2,6,6-tetramethyl-3,5-heptanedione (Hthd), LnCl(3)center dot 6H(2)O and neutral ligands. The single crystal X-ray diffraction analysis confirms that the Dy(III) ions of complexes 1 and 2 are seven-coordinated with N1O6 coordination environment, forming C-3v and C-2v local symmetry. Magnetic studies reveal that mononuclear complex 1 displays butterfly-shaped hysteresis loops at 1.8 K and slow relaxation of magnetization with energy barrier 34.7 K in optimized external filed while dinuclear complex 2 not exhibits single-molecule magnet (SMM) behavior. The variable temperature magnetic data of dinuclear Gd(III) analogues (3) indicate the negligible intramolecular magnetic interactions between the two Gd(III) centers in structure due to long Ln center dot center dot center dot Ln distance. The diluted sample by Y(III) ions of complexes 1' and 2' and electrostatic model calculation were employed to elucidate distinction of magnetic properties. Investigation of magneto-structural correlation emphasizes that the orientation of the magnetic axis affects the magnetic properties, which is further associated with local symmetry of the Dy(III) ions.