Macrocycle supported dinuclear lanthanide complexes with different β-diketonate co-ligands displaying zero field single-molecule magnetic behaviour

Abstract

Three different sets of isomorphous dinuclear Gd/Dy complexes, [Ln₂(L′)(acac)₄]·2H₂O·2CH₃CN (Ln = Gd (1_Gd) and Dy (2_Dy); acac = acetylacetonate), [Ln₂(L′)(tfac)₄] (Ln = Gd (3_Gd) and Dy (4_Dy); tfac = trifluoroacetylacetonate), and [Ln₂(L′)(hfac)₄] (Ln = Gd (5_Gd) and Dy (6_Dy); hfac = hexafluoroacetylacetonate), where H₂L′ is a new Ln-assisted in situ generated macrocyclic ligand from acyclic Schiff base HL, derived from a condensation reaction of 2,6-diformyl-4-methylphenol and N,N-dimethyldipropylenetriamine, have been synthesized by the reaction of lanthanide nitrates with ligand HL in the presence of different β-diketonate co-ligands. Structural analysis revealed that the lanthanide ions in these complexes are all eight-coordinated in a square antiprismatic geometry with D_4d symmetry. Magnetic measurements of these complexes revealed that the magnetic interaction between Gd³⁺ ions is antiferromagnetic, while Dy³⁺ ions are ferromagnetically coupled in dimetallic complexes, and the detailed analysis of Gd analogues discloses the significant influence of the different β-diketonate co-ligands on the magnitude of the magnetic interactions. All three Dy complexes exhibit zero field single-molecule magnet behaviour with energy barriers varying in the close range 60.1–62.8 K. The orientation of the magnetic axes and crystal structural parameters were critically analysed to establish magneto-structural correlations in three Dy-based SMMs to gain an in depth understanding of the magnetic dynamics in these systems.