Octanuclear {Ln8} complexes: magneto-caloric effect in the {Gd8} analogue

Two neutral, isostructural, octanuclear, LnIII complexes, [Ln8(HL)6(L)2(μ3-OH)4(μ2-OH)2(H2O)4].solv (Ln = Gd(III), (1Gd) and Dy(III), (2Dy) have been synthesized using LnIII nitrate salts and a o-vanillin-supported multi-dentate ligand, N'-(2-hydroxy-3-methoxy-5-nitrobenzylidene)-2-(hydroxyamino) propanehydrazide (H3L) in the presence of tetramethyl ammonium hydroxide. The complexes were structurally characterized by single crystal X-ray diffraction studies. The complexes are held by the cumulative coordination action of six [HL]2−, two [L]3− chelating ligands, H2O and hydroxide ligands. Magneto-structural analysis of complexes 1Gd and 2Dy reveals the presence of intramolecular antiferromagnetic interactions between the LnIII ions. Magneto-caloric effect was analysed for the complex 1Gd which shows a maximum in the change of molar entropy (–ΔSm) of magnitude 25.5 J kg–1 K–1 at T = 3 K and an applied field change ΔB = 5 T.