Synthesis,Structures And Luminescent/Magnetic Properties Of Multinuclear RE Complexes

The study of rare-earth complexes has been a hot topic in recent years.In this dissertation,two new ligands,2-[[（1,2,4-triazole）-4-imino]methyl]-8-hydroxy-quinoline（HL1）and 5-（2-furanimino）-8-hydroxyl-quinoline（HL2）,and two reported ligands,5-（2-hydroxybenzalimino）-8-hydroxylquinoline（HL3）and 2,6-bis[（2-hydroxy-3-methoxybenzylidene）-hydrazinocarbonyl]pyridine（H₄L4）,were adopted.And three series of dinuclear,tetranuclear and hexanuclear complexes were obtained by these four ligands and characterized by X-ray single crystal structure determination,powder X-ray diffraction,thermogravimetric analysis and UV-Vis absorption.The near-infrared fluorescence and magnetic properties of the complexes were studied emphasically.1.Four dinuclear complexes,Ln₂（dbm）₄（L1’）₂（Ln=Tb（1）,Dy（2）,Ho（3））and Yb₂（dbm）₄（L1）₂（4）,were obtained by HL1.The alternating current susceptibility measurements reveal that 2 displays single-molecule-magnet behaviors with effective energy barrier of U_eff=61.7 K(Ï„₀=1.8×10^-7 s)under a zero direct-current field.The ligand-exchange that HL1 was transformed to methyl-8-hydroxyquinoline-2-carboxylate（HL1’）when coordinated to Rare-earth ions in methanol solution is rare in organic reactions and coordination chemistry.2.Complexes 5-16,[RE₄（acac）₄（L2）₆（μ₃-OH）₂]·n CH₃CN（n=2 for RE=Y（5）,Dy（6）,Ho（7）,Lu（8）;n=0 for RE=Eu（9）,Tb（10）;n=1 for RE=Er（11）;n=8 for RE=Yb（12））,[RE₄（dbm）₄（L2）₆（μ₃-OH）₂]n CH₃CN（n=0 for RE=Y（13）,Dy（15）;n=1 for Eu（14））and[Yb₂（dbm）₄（L2）₂]·2CH₃CN（16）,were synthesized by HL2 and Rare-earthβ-diketonate.Complex 11 in the solid-state displays typical emissions of the Er^â…¢ in the NIR region under 350 nm excitation,while complexes 12 and 16 fail to be excited.It indicates that the excited triplet energy level of the ligand matches the resonance energy level of the Er^â…¢ but not with that of Yb^â…¢,and suggests the potential application of complex 11 in NIR technology.3.The alternating current susceptibility measurements reveal that complexes 6and 15 both exhibit single-molecule magnet behavior.Complex 15 displays single-molecule-magnet behaviors with effective energy barrier of U_eff=117.4 K(Ï„₀=1.79×10^-8 s)under a zero direct-current field and effective energy barrier of U_eff=123.3 K under a direct-current field of 1500 Oe,while 6 presents two distinct slow magnetic relaxation processes with effective energy barriers of U_eff=162.1 K for the fast relaxation（FR）process(Ï„₀=8.53×10^-11 s)and U_eff=165.3 K for the slow relaxation（SR）process(Ï„₀=1.14×10^-9 s),which demonstrates that the subtle changes of coordination environment can drastically influence the overall magnetic properties.4.Eight tetranuclear rare-earth complexes 17-24,[Ln₄（acac）₄（L3）₆（μ₃-OH）₂]（Ln=Dy（17）,Ho（18）,Er（19）,Yb（20））and[Ln₄（dbm）₄（L3）₆（μ₃-OH）₂]·n CH₃COCH₃（n=0 for Ln=Dy（21）,Er（22）;n=3 for Yb（23）;n=2 for Yb（24））,were synthesized by HL3.The effective energy barrier of the complex 17 under a zero direct-current field is 142.5 K,while the effective energy barrier of complex 21 is123.04 K with alteringβ-diketonate.5.Six hexanuclear complexes 25-30,[Ln₆（H₂L4）₂（L4）₃（acac）₂（H₂O）₂（DMF）₂]（Ln=Dy（25）,Tb（26）,Er（27））and[Ln₆（H₂L4）₂（L4）₃（tfa）₂（DMF）₂（H₂O）CH₃OH]（Ln=Dy（28）,Tb（29）,Er（30））,were synthesized by H₄L4 as ligand.Under a zero direct-current field,complexes 25 and 28 exhibits temperature and frequency dependence without significant peaks.The dynamic magnetic properties of the complexes 25 and 28 under the applied dc field show that both the two complexes exhibit single-molecule magnet behavior with effective energy barriers of 64.0 K and66.5 K,respectively.Quantum tunneling caused by the dipole-dipole interaction can be responsible for the remaining quantum tunneling in complexes 25 and 28 with the applied dc field.