Five new tetranuclear complexes based on an 8-hydroxyquinoline Schiff base derivative and the β-diketone coligand, [Ln(acac)L(μ-OH)]·CHCN·0.5CHCl (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5); HL = 5-(benzylidene)amino-8-hydroxyquinoline; acac = acetylacetonate) have been synthesized, and structurally and magnetically characterized. Complexes 1-5 have similar tetranuclear structures. Each Ln ion is eight coordinated and its coordination polyhedra can be described as being in a distorted square-antiprismatic geometry. The magnetic studies reveal that 1 features the magnetocaloric effect (MCE) with the magnetic entropy change of -ΔS(T) = 25.08 J kg K at 2 K for ΔH = 7 T, and 3 displays the slow magnetic relaxation behavior of Single Molecule Magnets (SMMs) with the anisotropic barrier of 86.20 K and the pre-exponential factor τ = 2.99 × 10 s.
Five tetranuclear lanthanide complexes [Gd(dbm)(L)(μ-OH)]·5CHCN (1), [Tb(dbm)(L)(μ-OH)]·2CHCHOH·4CHCN (2), [Dy(dbm)(L)(μ-OH)]·4CHCN·2HO (3), [Ho(dbm)(L)(μ-OH)]·CHCHOH·4CHCN·2HO (4) and [Er(dbm)(L)(μ-OH)] (5) are obtained from the reaction of 5-(4-pyridinecarboxaldehyde)amino-8-hydroxylquinoline (HL) and Ln(dbm)·2HO (dbm = 1,3-diphenyl-1,3-propanedione). Complexes 1-5 are isomorphous and crystallize in the monoclinic space group P2/c. The metal ions in 1-5 adopt an approximately square-antiprismatic coordination environment. Magnetic studies indicate that complex 1 features a magnetocaloric effect (MCE) with the magnetic entropy change of -ΔS(T) = 16.35 J kg K at 3 K for ΔH = 7 T. Additionally, complex 3 displays single molecule magnet (SMM) behavior, exhibiting an effective energy barrier of the relaxation of magnetization U/k = 89.38 K and pre-exponential factor τ = 3.32 × 10 s.
Nine new tetranuclear centrosymmetric linear complexes, [RE(dbm)L(DMF)]·nCHCl·mCHN (RE = Y (1), Tb (2), Dy (3), Ho (4), Er (5), Lu (6)) and [RE(dbm)L(CHOH)]·nCHCN (RE = Tb (7), Dy (8), Ho (9)) (HL = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-8-hydroxyquinoline and dbm = 1,3-diphenyl-1,3-propanedione) have been synthesized. Complexes 1-9 are tetranuclear complexes. Magnetic studies reveal that both Dy-based complexes (3 and 8) exhibit single-molecule magnet (SMM) behavior under a zero dc field. Furthermore, complex 3 presents one relaxation process under a zero dc field, while application of an external dc field (1500 Oe) induces multi-relaxation signals of the ac magnetic susceptibility.
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