Synthesis And Magnetic Properties Of Lanthanide Complexes Based On Polydentate Schiff Base Ligands

Lanthanide complexes,especially the single-molecule magnets（SMMs）and magnetic refrigeration materials have become the hotspots because of their potential applications in magnetism.In this paper,thirteen tetranuclear and two dinuclear lanthanide complexes have been synthesized by using three Schiff base derivative ligands and four ancillaryβ-diketones co-ligands and have been characterized structurally and magnetically.The main results are as following:1.The research progress of the SMMs,lanthanide SMMs and magnetic refrigeration materials has been described briefly.2.Ten tetranuclear lanthanide complexes,[Ln₄（μ₃-OH）₂（L1）₆（acac）₄]·2.5CH₃CN（Ln=Gd（1）,Tb（2）,Dy（3）,Ho（4）andYb（5））,[Ln₄（μ₃-OH）₂（L1）₆（tmhd）₄]·xCH₃CN·yCH₃CH₂OH（Ln=Eu（6）,Gd（7）,and Tb（8）,x=1,y=1;Ln=Dy（9）,x=2,y=0）and[Dy₄（μ₃-OH）₂L₆（beac）₄]·CH₃CN（10）have been synthesized through an 8-hydroxyquinoline Schiff base derivative HL1（HL1=5-[（4-methoxyphenyl）methylene]amino-8-hydroxylquinoline）and three ancillaryβ-diketones co-ligands（Hacac=acetylacetone;Htmhd=2,2,6,6-tetramethyl-3,5-heptanedione;Hbeac=1-benzoylacetone）by volatilization method.The magnetic study reveals that 1·Gd and 7·Gd exhibit magnetothermal effect with the-ΔS_m values of 19.39（2）J K^-1 kg^-1 for 1·Gd and16.21（3）J K^-1 kg^-1 7·Gd（T=2 K,ΔH=7 T）.Additionally,steric-hindrance effect on the magnetic anisotropy of the Dy³⁺centers in 3·Dy,9·Dy and 10·Dy results in their different SMMs behaviors with energy barriers of 99.29（3）K for 3·Dy,64.56（4）K for 9·Dy and61.05（0）K for 10·Dy.3.Three tetranuclear lanthanide complexes,[Ln₄（μ₃-OH）₂（tmhd）₄（L2）₆]·2CH₃CN（where Ln=Eu（11）,Gd（12）and Dy（13））have been synthesized through an 8-hydroxyquinoline Schiff base derivative HL2（HL2=5-[（phenylmethylene）amino-8-hydroxylquinoline）and an ancillaryβ-diketone co-ligand Htmhd by volatilization method.Investigations on luminescent properties and lifetime of 11·Eu display characteristic emission peaks of Eu³⁺ion and the average luminescent lifetime is 9.26μs.Detailed magnetic studies suggest that 12·Gd exhibits magnetothermal effect with the-ΔS_m value of 17.94 J K^-1 kg^-1（T=2 K,ΔH=7 T）and 13·Dy exhibits SMMs behaviors with energy barriers of 35.8 K.The sistitue groups of HL1 and HL2are different,leading to a big difference of the energy barrier in complexs 9·Dy and 13·Dy.This could illustrate that the change of sistitue groups of the ligands may have evident impact on the magnetic relaxation behaviors of the complexes.4.Two dinuclear lanthanide complexes,[Ln₂（L3）（dbm）₄]·2CH₃OH（Ln=Gd（14）and Dy（15）have been synthesized through an bis-（o-vanillin）Schiff base derivative H₂L3（H₂L3=N,N’-bis（3-methoxysalicylidene）-1,3-diamino-2-propanol））and an ancillaryβ-diketones co-ligand Hdbm（Hdbm=1,3-diphenyl-1,3-propanedione）by volatilization method.The magnetic studies reveal that 14·Gd exhibits magnetothermal effect with the-ΔS_m value of18.95（2）J K^-1 kg^-1（T=2 K,ΔH=7 T）and 15·Dy exhibits slow magnetic relaxation behaviors with strong quantum tunneling of the magnetization（QTM）,resulting in a small energy barrier value of 0.73（1）K.