Ligand field and anion-driven structures and magnetic properties of dysprosium complexes

Abstract

Based on the organic ligand 2,2′-(((pyridine-2,6-diylbis(methylene))bis((pyridin-2-ylmethyl)-azanediyl))-bis(methylene))diphenol (H₂L), and dysprosium salts with different anions, two mononuclear and one dinuclear complexes, namely, [Dy(L)(H₂O)](ClO₄)·2CH₃CH₂OH (1), [Dy(L)(NO₃)] (2) and [Dy₂(L)(dbm)₄] (3, Hdbm = dibenzoylmethane), were synthesized and structurally and magnetically characterized. In complexes 1 and 3, the Dy centers are octa-coordinated with triangular dodecahedral (local D_2d symmetry) environments. Complex 1 is dimeric by hydrogen bond interactions between coordinated water molecules. In complex 3, two Dy^III ions are linked by two phenoxy oxygen atoms to form a dinuclear cluster. The Dy^III ion in complex 2 is nine-coordinated and adopts a spherical capped square antiprism geometry with a C_4v symmetry. Magnetic measurements and theoretical calculations reveal that the magnetic couplings between two phenoxyl-bridging Dy^III ions in complex 3 are antiferromagnetic and mostly originate from the exchange coupling. Both complexes 1 and 2 exhibit single molecule magnet behaviors under zero direct-current field with effective energy barriers of 50.94 K and 12.26 K, respectively. Complex 3 only exhibits frequency-/temperature-dependent out-of-phase signals, and no peak is observed.