Syntheses, structures, and magnetic properties of homodinuclear lanthanide complexes based on dinucleating Schiff base ligands

Abstract

The first two families of homodinuclear lanthanide(III) complexes, formulated as [(L_OEt)₂Ln₂(L1)] and [(L_OEt)₂Ln₂(L2)] (Ln³⁺ = Dy³⁺, Tb³⁺, Ho³⁺, Gd³⁺, and Y³⁺; L1⁴⁻ = 2,2′,2′′,2′′′-[1,2,4,5-benzenetetrayltetrakis(nitrilomethylidyne)]tetrakisphenolate; L2⁴⁻ = 2,2′,2′′,2′′′-[[1,1′-biphenyl]-3,3′,4,4′-tetrayltetrakis(nitrilomethylidyne)]tetrakis(4-chlorophenolate); L_OEt⁻ = (η⁵-cyclopentadienyl)tris(diethylphosphito-p)cobaltate(III)), were successfully synthesized based on Kläui's tripodal building block NaL_OEt and two dinucleating Schiff base ligands, H₄L1 and H₄L2, respectively. Single-crystal X-ray analyses show that these lanthanide complexes have two seven-coordinated metal binding sites, linked to each other with a phenyl or biphenyl bridge. Variable temperature dc magnetic measurements reveal the weakly antiferromagnetic coupling between paramagnetic lanthanide ions, while ac magnetic data exhibit the field-induced relaxation of magnetization for the corresponding Dy₂ complexes 1 and 6. A further magnetic dilution study for 1 suggests that the slow magnetic relaxation originates from the single-ion magnetic behaviour of Dy³⁺ ions.