MOFs Based On Pyridine Polycarboxylic Acid And Tetrazolcae Ligands: Luminescence Sensing Properties And Magnetic Studies

Metal-organic frameworks（MOFs）,also known as coordination polymers,is a new type of crystalline porous materials with broad applications in catalysis,fluorescence sensing,magnetism,bio-imaging,drug release and gas storage.In recent years,in addition to the study of classical MOFs,the synthesis of new MOFs with unique structures by self-assembly of different ligands and various metal ions,and the study of their properties have become one of the active hot topics.In this thesis,we used a pyridinyl-tricarboxylate（H₃L=（3’,5’-dicarboxylphenyl）nicotinic acid）and pyridinyl-tetrazolate（L=4-（tetrazol-5-yl）phenyl-4,2’:6’,4’’-terpyridine）respectively as the main ligands,obtained seven MOFs under the solvothermal conditions by the self-assembly of these two ligands with Ln³⁺and Co²⁺ions.The specific study contents are as follows:1.Five3DisomorphousLn-MOFsweresynthesizedbyusing pyridinyl-tricarboxylateligandH₃LandEu（NO₃）₃·6H₂O,Tb（NO₃）₃·6H₂O,Sm（NO₃）₃·6H₂O,Gd（NO₃）₃·6H₂O and Dy（NO₃）₃·6H₂O.Based on the good luminescence properties of Eu-MOF（1）and Tb-MOF（2）,we conducted the fluorescence sensing experiments on them respectively.We found that Eu-MOF（1）and Tb-MOF（2）could not only detect Fe³⁺ions with high sensitivity and selectivity in water system,but also could detect acetone molecules in water system.We also further studied the sensing properties of Fe³⁺ions by Eu-MOF（1）and Tb-MOF（2）in the simulated physiological buffer,and found that Eu-MOF（1）and Tb-MOF（2）could still realize efficient,rapid and selective sensing of Fe³⁺ions,which is of great significance for the detection of Fe³⁺ions in the living organisms in the future.2.Based on the five isomorphous Ln-MOFs synthesized in previous chapter,since in the structures of Ln-MOFs,there contains 1D chains which are alternately bridged by double and quadruple carboxylate bridges,and the magnetic orbitals of Ln³⁺have the characteristics of a single electron,we conducted magnetic studies in the five complexes respectively.Magnetic studies indicate weak magnetic interactions in Eu-MOF（1）.The main magnetic transfer between Tb³⁺ions are antiferromagnetic interactions in Tb-MOF（2）.The decrease of theχT values of Sm-MOF（3）was attributed to the thermal depopulation of the excited states.While for Gd-MOF（4）and Dy-MOF（5）,the main magnetic transfer are ferromagnetic interactions between Gd³⁺ions and Dy³⁺ions.Moreover,Dy-MOF（5）also exhibits slow magnetic relaxation behavior to some extent in the ac field.3.Two Co-MOFs,Co-MOF（6）and Co-MOF（7）were synthesized by using pyridinyl-tetrazolate ligands L and Co（NO₃）₂·6H₂O under solvothermal conditions.The linear[Co₃（tetrazolate）₆（H₂O）₂]units with（μ-N-N-tetrazolate）₃ bridges are interlinked by the L ligands into 2D networks in the structure of 6.It has been demonstrated that the triple bridges mediate antiferromagnetic coupling between the Co（II）ions.Compound 7 features the unprecedented 1D non-uniform angular magnetic chain formed from scalene triangle with mixedμ₃-OH,and（μ₃-OH）（μ-N-N-tetrazolate）₂ bridges.The 1D chains are interlinked by the big and rigid organic ligands into a 2D network.The magnetic properties of 7 indicate the coexistence of 1D ferrimagnetic chains,slow magnetic dynamics and large hysteresis.