Synthesis,Structure And Properties Of Metal Cluster Based On 5-Bromo-o-vanillin Polyhydroxy Schiff Base

In recent years,hydroxy Schiff base clusters have attracted much attention not only for their structural novelty,but also for their potential applications in luminescent materials,magnetic materials,nonlinear optical materials,and biological systems.The hydroxyl Schiff base ligand has both a nitrogen atom coordinated with a transition metal and an oxygen atom coordinated with a rare earth metal.Therefore,the hydroxyl Schiff base is one of the best ligands for constructing heteronuclear clusters.In this thesis,nine clusters of three series,homo-and hetero-nuclear,were prepared by self-assembly using5-bromo-o-vanillin-2-amino-2-methyl 1,3-propanediol as the main ligands;the structure of clusters was characterized and the fluorescence and free radical scavenging properties of clusters were further studied.The specific content is divided into the following four parts:1.Introduce the research progress of Schiff base clusters.2.First,5-bromo-o-vanillin was condensed with 2-amino-2-methyl-1,3-propanediol to obtain a new polyhydroxy Schiff base ligand,that is 5-bromo-o-vanillin 2-amino-2-Methyl-1,3-propanediol?H₃L?,and then reacted with the rare earth salt to prepare two homotetranuclear rare earth clusters by solvent diffusion method,whose molecular formula is[Ln₄??₄-O??HL?₄?CH₃OH?₄]?NO₃?₂{Ln=Dy?1?,Nd?2?}.The structure analysis shows that the two clusters are actually a square center-symmetric cluster structure formed by a proton-free ligand(HL^2-)and ?₄-O bridging four rare earth ions.The fluorescence peaks of the ligands appeared in the solid fluorescence mass spectra of the two clusters,and two ionic fluorescence characteristic peaks of Dy^? appeared in cluster 1,indicating that the ligand can sensitize the rare earth ion Dy ^? to emit light.Only the fluorescence peaks of the clusters 1 and 2 ligands appeared in the DMF solution,which indicates that the DMF solvent blocked the energy transfer of the ligands to the rare earth;The IC₅0 values for scavenging hydroxyl radicals of clusters 1 and 2 are 25.6 and 20.6?M,while the IC₅0 values for scavenging superoxide radicals of cluster 2 is 10.1?M,indicating that the clusters 1 and 2 have good activity of scavenging hydroxyl groups and superoxide radicals.3.Zinc ions were introduced on the basis of the same tetranuclear rare-earth cluster,and four heterohepta-core zinc-rare earth clusters were prepared by solvothermal method.The molecular formula is:[Zn₄Ln₃?L?₄?HL?₂?CH₃O?]?CH₃OH{Ln=Sm?3?,Eu?4?,Tb?5?,Dy?6?}.Single crystal structure analysis showed that the four clusters were heterogeneous and isomorphic.A protonated ligand(L^3-,HL^2-)bridged four zinc ions and three rare earth ions to form a seven-core cluster structure in the shape of a butterfly.Further research on the solid fluorescence properties of clusters 3-6 led to the following conclusions:cluster 3 appears with two ionic fluorescence characteristic peaks of Sm^?,cluster 4 appears with five ionic fluorescence characteristic peaks of Eu^?,and cluster 5 appears one ionic fluorescence characteristic peak of Tb^?,and cluster 6 does not show the ionic fluorescence characteristic peak of Dy ^?,indicating that the H₃L ligand can selectively sensitize the rare earth ion to emit light,and the order of sensitization efficiency is:Eu^?>Sm^?>Tb^?>Dy^?;In the DMF solution,due to the solvent quenching,the ionic characteristic fluorescence peaks of clusters 3,5,and 6 did not appear.Only the two ionic characteristic fluorescence peaks of cluster 4 namely Eu ^? appeared;The IC₅0 value of the clusters 3,4,5 and 6 for scavenging hydroxyl radicals is 14.3²1.2?M;The IC₅0 value of cluster 3 for scavenging superoxide radicals is 20.9?M.The results show that cluster 3-6 can effectively scavenge hydroxyl and superoxide radicals.On the basis of homotetranuclear clusters,zinc ions were introduced to control the structure and properties of the clusters.4.On the basis of zinc-rare earth heteronuclear clusters,the secondary ligand niacin was introduced,and three isododecuclide zinc-rare earth clusters were prepared by a natural volatilizationmethod.Themolecularformulais:[Zn₈Ln₄?L?₆?HL?₂?H₂L?₂?NA?₂?CH₃COO?₂?CH₃OH?₂]{Ln=Eu?7?,Tb?8?,Dy?9?}.Structural analysis showed that the main protons(L^3-,HL^2-,H₂L^-)and the secondary ligand nicotinic acid?HNA?bridged four rare earth metals and eight zinc ions to form a twelve-core symmetrical central structure.The solid fluorescence spectra of clusters 7-9 prove that cluster 7 shows five ionic characteristic fluorescence peaks of Eu^?,cluster 8 shows one ionic characteristic fluorescence peak of Tb^?,and cluster 9 does not appear the characteristic fluorescence peak of Dy^?.It shows that the ligand can sensitize the rare earth ion to emit light,but the sensitization efficiency is different,which is Eu^?>Tb^?>Dy ^?.In DMF solution,the ionic characteristic fluorescence peaks of clusters 8 and 9 did not appear,only cluster 7showed two ionic characteristic fluorescence peaks of Eu^?,which proved that the interaction between solvent molecules and clusters would partially block the energy transfer efficiency of metals and ligands,which further weakens the characteristic fluorescence peak of the rare earth ion or makes it disappear.The IC₅0 value of cluster 7-9 for scavenging superoxide radicals is 51.6⁶4?M,and the IC₅0 value of scavenging hydroxyl radicals is 11.3¹3.9?M.Cluster 7-9 has good radical scavenging activity.The number of nuclei of clusters increased and the properties became more excellent after the introduction of the secondary ligand niacin on the basis of heteroheptanucleus clusters.