Synthesis,structure And Property Of Transition Metal Complexes Based On 3,4-Dicarboxylbenzene Derivatives

Complexes have shown great potential applications in the fields of adsorption and separation,proton conduction,catalytic degradation,luminescence sensing and so on,due to their diverse structures,strong designability,and the ability of framework structure to interact with guest molecules.In this paper,two aromatic polycarboxylic acid compounds with different rigidity were selected as organic ligands,and 11 transition metal complexes with abundant d electrons were synthesized by aqueous/solvothermal methods,and their structures were characterized by X-ray single crystal diffraction.The applications of Cu（II）complexes with d⁹ electronic configuration in catalytic degradation and Zn（II）/Cd（II）complexes with d¹⁰ electronic configuration in fluorescence sensing were further explored.At the same time,the relationship between the framework structure and properties of the complexes was analyzed and summarized.The main research contents and results are as follows:（1）Three novel Cu（II）complexes 1-3 were synthesized by hydrothermal method for the degradation of methylene blue（MB）using 6-（3′,4′-dicarboxyphenoxy）-1,2,4-benzenetricarboxylic acid as organic ligand and bridging nitrogenated auxiliary ligands.In the presence of H₂O₂,complexes 1-3 exhibited efficient and stable catalytic degradation performance of MB in weak alkaline/basic solutions as heterogeneous catalysts,with rate constants of 0.069,0.402 and 0.133 min^-1,respectively.The excellent degradation performance was attributed to the Fenton-like reaction between the active sites of copper ions in complexes 1-3 and H₂O₂,and the organic linker acted as a photo-antenna,which absorbed light to generate oxidized holes（h⁺）and reduced electrons（e^-）.In addition,the effects of initial MB concentration,catalyst dosage,p H value and H₂O₂ concentration on the degradation of MB were investigated and analyzed in detail.The results showed that these factors had great influence on the degradation performance of complexes 1-3.（2）Five novel luminescent complexes 4-8 were synthesized by the reaction of semi-rigid 6-（3′,4′-dicarboxyphenoxy）-1,2,4-benzenetricarboxylic acid or rigid 3,5-bis（3,4-dicarboxyphenyl）pyridine,and different nitrogenated auxiliary ligands,as well as Cd（II）ions.The fluorescence sensing studies showed that these complexes can be used as fluorescence sensing materials in aqueous media.Among them,complexes 6-8 can achieve qualitative and quantitative detection of Zn²⁺ions by fluorescence enhancement effect,with detection limits of 89.5,67.6 and 26.1 n M,respectively.Even in the presence of other metal ions in the detection system,complexes 6-8 still showed excellent recognition ability for Zn²⁺ions.Compared with complexes 6 and 7 based on the semi-rigid aromatic polycarboxylic acid,complex 8 constructed by the rigid aromatic polycarboxylic acid exhibited better sensing performance,indicating that the sensing performance of the complex can be effectively improved by adjusting organic ligands.（3）The Cd（II）complex 9 with good thermal and p H stability was synthesized using the rigid organic ligand 3,5-bis（3,4-dicarboxyphenyl）pyridine.Complex 9 can be used as a potential lanthanide ions fluorescence sensing material due to its rigid frame structure and the presence of uncoordinated carboxyl oxygen atoms.Under the influence of energy transfer mechanism,complex 9 can quantitatively detect La³⁺/Eu³⁺/Tb³⁺/Dy³⁺in aqueous solution through different sensing behaviors,with detection limits of 0.44μM,0.11μM,1.20 n M and 0.59μM,respectively.In addition,the sensing behavior of complex 8 with the same main ligand for lanthanide metal ions was further investigated,and the results showed that complex 8 also exhibited high sensitivity to Eu³⁺and Tb³⁺in aqueous solution,with detection limits of 0.35μM and 10.9 n M,respectively,which was slightly inferior to complex 9.The difference in sensing properties of complexes 8 and 9 can be attributed to the differences in the energy transfer efficiency between the complex frame structure and the lanthanide ions.Due to their high sensitivity to lanthanide ions,complexes 8 and 9 can be used as candidate materials for lanthanide ions sensing.（4）Two complexes 10 and 11 with excellent luminescence properties were synthesized by the reaction of rigid 3,5-bis（3,4-dicarboxyphenyl）pyridine with Zn（II）ions and phenanthroline（phen）/2,2′-bipyridine（2,2′-bipy）as nitrogenated auxiliary ligands.The photoluminescence study showed that the complexes 10 and 11 can be used as quenched fluorescence sensing materials for quantitative detection of Cu²⁺ions,and the detection limits were 74.6 and 301.7 n M,respectively,which can meet the practical detection requirements.In addition,the complexes 10 and 11 also showed excellent fluorescence quenching performance for Cu²⁺ions in HEPES buffer solution.It is worth noting that complexes 10 and 11 have good accuracy in the detection of Cu²⁺ions in actual water samples,which indicates that complexes 10 and 11 are fluorescence sensing materials with practical application.