| The desire to miniaturize the nanoregime devices,including high-desinty information storage,spintronics,magnetic refrigerator and quantum computation,has led to the persistent efforts for the investigation of single molecule magnets?SMMs?.Among the factors that affect the performance of single-molecule magnets,the selection and design of ligands are the key factors.Schiff base ligands are often chosen as ligands for single-molecule magnets because of their rich coordination sites and tunable properties.Among all the organic ligands,the Schiff-bases are the most used one.In this thesis,some diphenol Schiff-bases have been used as ligands and 30 complexes were synthesized by solvothermal method.Magnetic properties of some of these complexes were studied.The performance of Tb4 complex in fluorescence detection of ions and nitrobenzene derivatives were investigated.The main results are summarized as follows:1.The utilization of 2-ethoxy-6-???2-hydroxy-3-methoxybenzyl?imino?methyl?phenol?H2L1?as a chelating ligand,in combination with employment of EtOH or MeOH as auxiliary ligands,in the 4f-metal chemistry afforded two series of dinuclear lanthanide complexes with formulas Ln2?L1?2?NO3?2?C2H5OH?2?Ln=Sm?1?,Eu?2?,Gd?3?,Tb?4?,Dy?5?,Ho?6?,Er?7??and Ln2?L1?2?NO3?2?CH3OH?2?Ln=Sm?8?,Eu?9?,Gd?10?,Tb?11?,Dy?12?,Ho?13?,Er?14??.The slight difference between 1-7 and 8-14 stems from purposefully replacing the EtOH ligands in 1-7 with MeOH in 8-14.Complexes 5 and 12exhibit SMMs behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12,respectively.The calculated results were performed on two Dy2 complexes.Subtle variation in the angle?between the magnetic axes and the vector connecting two DyIII ions results in the weaker influence on the tunneling gap of individual DyIII ions by the dipolar field in 12.2.Threenewdinucleardysprosiumcomplexesofformulas[Dy2?L2?2?NO3?2?CH3OH?2]·2CH3OH?15?,Dy2?L3?2?NO3?2?CH3OH?2?16?and[Dy2?L4?2?HL4??NO3?]·CH3OH?17?,?H2L2=4-chloro-2-???2-hydroxy-3-methoxybenzyl?imino?methyl?phenol,H2L3=2-???2-hydroxybenzylidene?amino?methyl?-6-methoxyphenol,H2L4=2-???2-hydroxy-3-methoxybenzyl?imino?methyl?-5-methoxyphenol?)havebeen synthesized through employing three Schiff base ligands.X-ray crystallographic analysis revealed that complexes 15-17 are all in NO7 coordination environments.DyIII ion is in D2dd local symmetry in 15 while DyIII ion is in D4d local symmetry in 16.In asymmetric complex 17,Dy1 center is in D2d local symmetry and Dy2 center in D4d local symmetry.Complexes 15-17 exhibit SMM behaviors with energy barriers of 51.97 K,87.16 K and167.14 K,respectively.Theory calculations were performed on three Dy2 complexes to rationalize the observed difference in the magnetic behavior.Theory calculations reveal that the increase of the exchange magnetic interactions is the vital factor for complex 17 to exhibit the best energy barrier.3.Fivetetranuclearlanthanideclustersofcompositions[Ln4?L5?4?NO3?2?Piv?2]·2CH3OH?Ln=Gd?18?,Tb?19?,Dy?20?,Ho?21?,Er?22?;H2L5=2-???2-hydroxy-3-methoxybenzyl?imino?methyl?-6-methoxyphenol;Piv=pivalic acid?were synthesized under solvothermal conditions.Complexes 1-5 possess a zig-zag topology with[Ln4O6]cores being formed by the fusion of oxygen atom-bridged two[Ln2O2]moieties.Complex 20 exhibits single molecule magnet?SMM?behavior.The luminescence studies indicated that complex 19 can serve as highly sensitive and selective luminescent materials for Fe3+,CrO42-,Cr2O72-and 4-nitroaniline?4-NA?,demonstrating that complex 19 should be a pential candidate for multi-responsive luminescent sensor.4.TheemploymentofSchiffbaseligands2-???2-hydroxy-3-methoxybenzyl?imino?methyl?-6-methoxyphenol?H2L5?and2-???2-hydroxybenzylidene?amino?methyl?-6-methoxyphenol?H2L3?in the synthesis of CoII-LnIIIclustersisstudied.EightheteronuclearCoII-LnIIIcomplexes:[Co2Ln2?L5?2?OCH3?2?OAc?4]·CH3OH?Ln=Gd?23?,Dy?24?,Y?25??,[Co4Ln4?L5?2?L5??2??3-OH?4?OAc?6]·2C2H5OH?Ln=Gd?26?,Dy?27?,Y?28??,[Co4Ln2?L3?2??3-OH?4?NO3?2?CH3OH?]·4CH3OH?Ln=Dy?29?,Y?30??,have been prepared.The structures of the metal centers in the complexes are defect cubanes.The LnIIIII ions are located in the middle of the polynuclear metal center,while the CoII ions are distributed at both ends.Antiferromagnetic interactions were determined between the metal centers in 23-25 and 27.From the perspective of crystal engineering,we have successfully achieved the goals for synthesizing tetranuclear,hexanuclear as well as octanuclear complexes. |
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