Studies On Lanthanide Complexes And Their Optical And Magnetic Properties Based On The Benzene Carboxylic Acid Ligands

Rare earth organic coordination polymers have received considerable attentions due to their unique optical and magnetic properties,which are widely used in fields such as fluorescence sensing,magnetism,white light emitting devices,biological probes,and cell imaging.In this thesis,two kinds of benzene carboxylic acid ligands,1,4-（2’-carboxyphenyloxy）benzene（H₂bcpb）and 5-（hydroxymethyl）isophthalic acid（H₂hia）,are selected to react with lanthanide metal ions under solvothermal conditions,and 19coordination polymers are synthesized.The synthesized complexes are characterized in detail by infrared spectroscopy（IR）,elemental analyses（EA）,X-ray single crystal diffraction（XRD）,and X-ray powder diffraction（PXRD）;Subsequently,the complexes with excellent fluorescence performance are recorded through fluorescence sensing tests on organic small molecules and harmful heavy metal ions.Besides magnetic susceptibility of the complexes with single electron are investigated,and the coordination polymers with optical and magnetic dual functional properties are obtained.The main research results include the following two aspects:1.Eleven novel isomorphic binuclear two-dimensional coordination polymers[Ln₃（μ₃-bcpb）₃（μ₃-Hbcpb）₃（DMA）₃]_n（Ln=La,1;Ce,2;Pr,3;Nd,4;Sm,5;Eu,6;Gd,7;Tb,8;Dy,9;Ho,10;Er,11）were constructed from H₂bcpb ligand and lanthanide metal ions.They all crystallize in the space group P2₁/n of the monoclinic system.The lanthanide metal ions in this series of coordination polymers have a seven-coordinated pentagonal bipyramid geometry,and the topological symbol is{4³}₂{4⁶·6⁶·8³}.Thermogravimetric analyses show that the complexes have good thermal stability below 205℃.Based on the characteristic red and green lights of Eu（Ⅲ）and Tb（Ⅲ）ions of complexes 6 and 8,their applications in fluorescence sensing are further studied.The experimental results show that complexes 6and 8 can specifically detect acetone without interference from other small organic molecules,and their limits of detection（LODs）are 2.48×10^-3 M and 1.95×10^-3 M,respectively.Mechanism might be the competitive absorption of excited state energy between acetone and complexes.In addition,complex 8 can also be used as a sensor to detect Fe³⁺and PO₄^3-,with LODs of 3.40×10^-8 M and 4.38×10^-8 M,respectively.The mechanism exploration experiments show that the reason for Fe³⁺quenching the fluorescence intensity of complex 8 may be the synergistic effect of energy of competitive absorption,adsorption,and weak interaction.The specific response to PO₄^3-is due to the energy transfer between the ligand and the Tb³⁺center during excitation and the electrostatic interaction between PO₄^3-and Tb³⁺.The magnetic properties reveal that the coordination polymers from H₂bcpb ligand exhibit similar antiferromagnetic interactions(except for La³⁺and Gd³⁺complexes).Therefore,complexes 6 and 8 can be used as optical and magnetic dual-functional material.2.Eight new isomorphic binuclear three-dimensional coordination polymers[Ln₂（μ₃-hia）₃·2H₂O]_n（Ln=La,12;Ce,13;Pr,14;Nd,15;Sm,16;Eu,17;Gd,18;Tb,19）synthesized from H₂hia and lanthanide metal ions all crystallize in monoclinic systems,C2/c space groups.The lanthanide metal ions in this series of structures are eight-coordinated,showing a twisted dodecahedron,and the topological symbol is{4²·6}₂{4⁴·6²·8⁸·10}.The series of coordination polymers show good thermal stability below 320℃.Complexes 17and 19 can be used as fluorescent probes for the specific detection of acetone,and their LODs are 1.36×10^-3 M and 1.15×10^-3 M,respectively.The quenching mechanism may also be competitive absorption of energy.In addition,complexes 17 and 19 can specifically detect Cr O₄^2-/Cr₂O₇^2-with LODs of 7.20×10^-8/3.94×10^-8 M and 6.80×10^-9/2.50×10^-9 M,respectively.The quenching mechanism of Cr（VI）may be the competitive energy absorption.The LOD of 19 is lower than that of 17,due to the excitation energy of Tb³⁺is higher than Eu³⁺.During the detection process,the competitive absorption of energy between Cr（VI）and the ligand leads to the energy transfer from the ligand to Tb³⁺ions is more difficult than to Eu³⁺,and the"antenna effect"is weakened or prohibited,so the quenching effect of Cr O₄^2-/Cr₂O₇^2-on complex 19 is more obvious.Furthermore,the magnetic susceptibility of complexes is studied as a function of temperature.Both theχ_mT experimental values and the fitting results according to Curie-Weiss law show that there are antiferromagnetic interactions between neighboring lanthanide metal ions in such complexes.