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

Abstract 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 β-diketonate-based ligand 2,2,6,6-tetramethyl-3,5-heptanedione (Hthd), LnCl 3 ∙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 N 1 O 6 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⋅⋅⋅ 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.