The Properties Of Mono(hetero)-metallic Coordination Polymers Based On 2-imidazole(tetrazole)-terephthalic Acid Ligands

Coordination polymers（CPs）or metal-organic frameworks（MOFs）with rich frameworks and various intrinsic properties（porosity,adjustable frameworks,large surface area and exposed metal center,etc.）are a class of materials with the fastest-growing and broadly potential application at present.In reported MOFs,metal ions in various regions of the periodic table have been explored to synthesize monometallic MOFs,but the research on heterometallic organic frameworks（HMOFs）has not been particularly in-depth.Compared with monometallic MOFs,a special position is occupied by the heterogeneous metals in one HMOF,which will result in interesting network topologies,the synergistic effect between different metal ions makes the physical and chemical properties relatively enhanced,and even a HMOF has multiple functions.In this paper,seventeen functional MOFs were constructed by using asymmetric N-heterocyclic carboxylic acid ligands with similar skeleton and metal ions in the d-,f-and p-regions.This dissertation is mainly divided into five chapters as follows:Chapter 1 introduced the concept,synthesis strategy and performance prospect of MOF materials.Chapter 2 used metal ions in some areas of the periodic table and two ligands（H₂L1 and H₂L2）to prepare nine different characteristics MOFs.1 is a 0D structure with exposed carboxyl groups,2 and 3 are two 3D isomorphic frameworks with partially uncoordinated imidazole groups,4 is a 2D layered structure with incomplete coordination carboxyl groups,5 is a 3D microporous framework based on dinuclear paddle structure,and 6-9 are four 3D close packed structures.Based on the microporous framework of 5,we investigated the gas adsorption behavior of 5 at different temperatures and found that 5exhibited high adsorption selectivity for CO₂ and H₂.Chapter 3 took the preparation of MOFs 1 and 2 as precursors and according to the hard and soft acid-base theory（HSAB）,the anti-metallic ions were added,respectively.Then,two HMOFs 10 and 11 with different dimensions were obtained.Structural analysis showed that the four MOFs contained unsaturated catalytic centers,so they could be used as heterogeneous catalysts to enhance the efficiency of the addition reaction of CO₂ and epoxide derivatives.HMOFs showed higher catalytic performance than monometallic MOFs,and HMOF 11 with higher density of metal centers had better catalytic activity.In view of the tunability of this strategy,3 and 4 were selected as precursors and added anti-metallic ions respectively to obtain two kinds of HMOFs 12 and 13.In addition,HMOF 14 was obtained by one-pot method.Structural analysis presented that three 3D HMOFs are composed of different Dy（III）ion units and the same Co（II）ion units,and all of them contain 1D bimetallic channels.The HMOFs 12 and 14 underwent an irreversible thermally triggered single-crystal-to-single-crystal（SCSC）transformation to produce the HMOF 13 by different heating ways.Moreover,the results of variable temperature magnetic susceptibility test showed that Dy-Co HMOFs exhibited antiferromagnetic interaction.Synthetic strategies in this chapter have certain reference value for the preparation of various functional cluster-based HMOF materials.Chapter 4 employed a step-by-step strategy,the second Zn（II）ion was successfully introduced into MOF 7,and d-p HMOF 15 was obtained.Similarly,the HMOF 15 can also be prepared by one-pot method.Compared with the monometallic MOFs,the HMOF 15presented 3D micropores,and there were a large number of unsaturated bimetallic active sites in the pores.The gas adsorption test showed that the HMOF 15 took on a high adsorption capacity for CO₂,and separation effect under the equal molar ratio of gas molecules.In addition,HMOF 15 exhibited the excellent catalytic conversion efficiency of15 as catalyst for CO₂ cyclization.The synthesis framework could be optimized by functional groups modification,so as to improve its specific functions.Therefore,in this chapter,the similar skeleton H₂L2 was obtained by introducing the tetrazolium group into the H₂L1,replacing its original imidazole group.3D porous Pb-Zn HMOF 16 was prepared by one-pot method.Compared with the monometallic 8 and 9,HMOF 16 is a 3D microporous composed of planar bimetallic chains,and there are lewis basic sites（LBSs,bare N atoms）and lewis acid sites（LASs,unsaturated bimetallic sites）in pore.HMOF 16was used as catalyst for CO₂ cyclization under normal temperature and pressure,and its conversion efficiency reached more than 98%when epichlorohydrin was used as substrate.In addition,8 and 9 presented strong blue and weak yellow fluorescence,respectively,while HMOF 16 showed near white emission under the irradiation of UV lamp,which could be used in the research and development of new optical devices.This work is helpful to understand the characteristics of various metal elements at the molecular level,and has a certain guiding significance for the construction of functional monometallic MOFs and HMOFs.Chapter 5 exploited H₂L2 as functional ligand,a porous 17 with exposed tetrazolium group was constructed by isoreticular strategy.At 273 and 298 K,17 showed high adsorption capacity for N₂,CO₂,CH₄,C₂H₂,C₂H₄ and C₂H₆,and high selectivity for C₁/C₂.In view of the high specific surface area and pore size of the material,the material was used as a carrier and combined it with Au（III）ions to form Au@17 with appropriate reducing agent.The catalytic reduction of 4-nitrophenol（4-NP）was investigated by before and after loading of 17,Au@17 not only had good stability but also improved catalytic activity.