Series of dinuclear and tetranuclear lanthanide clusters encapsulated by salen-type and β-diketionate ligands: single-molecule magnet and fluorescence properties

Abstract

Three dinuclear [Ln₂H₂OL¹₂(acac)₂]·solvent (1, Ln = Gd, solvent = 2CH₂Cl₂; 2, Ln = Tb, no solvent; 3, Ln = Er, solvent = (C₂H₅)₂O), and two tetranuclear lanthanide clusters [Ln₄(μ₃-OH)₂L²₂(acac)₆]·2(solvent) (4, Ln = Tb, solvent = CH₃OH; 5, Ln = Dy, solvent = CH₃CN) were characterized in terms of structure, fluorescence and magnetism. The dinuclear lanthanide complexes were constructed by a rigid salen-type ligand H₂L¹ = N,N′-bis(salicylidene)-o-phenylenediamine and β-diketonate (acac = acetylacetonate) ligands, while the tetranuclear clusters were formed from the flexible ligand H₂L² = N,N′-bis(salicylidene)-1,2-ethanediamine. Crystal structure analysis indicates that the rigid ligand favors the double-decker sandwich structure (Ln₂L¹₂), in which the two lanthanide ions have different coordination numbers and geometry, while the more flexible ligand (H₂L²) leads to planar tetranuclear clusters. The relationship between their respective magnetic anisotropy and ligand-field geometries and their fluorescence properties was investigated. The Dy and Tb-containing clusters exhibit typical visible fluorescence properties, and single-molecule magnet behavior is seen in complex 5.