Study On Glass Transition And Iodine Capture Of Crystalline Complexes Constructed From Ligands With N Or O Donor Atoms

Crystal complexes have attracted much attention because of their unique functions.One of its main advantages is high designability: various types of metal ions and ligands can be selected.The high degree of designability of crystalline complexes has become an ideal platform for studying the transformation of crystalline structure,especially the hydrogen bond coordination network in which some solvent molecules(such as water)coordinating on metal nodes.Single-Crystal to Single-Crystal(SCSC)transformations are induced by the removal of coordinated small molecules,which means generation of unsaturated metal centers(UMC)or structural reorganization.In the process of structural reorganization caused by the departure of the coordination solvent,it is likely occurred the transition from oligomeric systems to porous coordination polymers(PCPs).PCPs,also call Metal-organic Frameworks(MOFs),are widely used in various fields because of their composition and porosity easy to control.However,the application of MOFs is greatly restricted due to their stability under harsh conditions and difficulty in processing and molding.Recently,there are obvious trends in the research of MOF:1.Directional design high stability MOF and put it into practical application;2.Further process and shape MOF materials to obtain the desired functional application.The directional design of high-stability functional MOF mainly relies on the wise choice of functional ligands and the construction of high-connectivity secondary building units.To make the MOF capable of molding,the crystalline MOF can only be melted into liquid by heating.After processing,it is cooled and formed.This method is only suitable for a little amount of MOF system.Based on our research team's previous accumulation of functionalized MOF design and solid-state structural transformation research,in this thesis we designed and constructed two functionalized MOFs with similar structures,and conducted in-depth studies on their structures and properties.At the same time,the structure of six reported mononuclear complexes and the porosity of the compounds with glass transition phenomenon have been preliminary explored.The first chapter is the foreword.It summarizes the development and research status of MOFs,analyzes the current scientific problems and challenges,introduces the research value and scientific significance of MOF glass,the research progress of MOF iodine and the current challenges.Finally,the significance of the topic selection of this topic is discussed,and the progress made by the topic group is presented.Chapter 2 introduces the use of linear nitrogen carboxylic acid ligands(Hina,Hpybz)and different metal ions to construct a series of M(ina)2(H2O)4(M = Cd,Mn,Co,Zn,Cu,Ni)and The transition metal crystalline complexes of Mn(pybz)2(H2O)4,and the glass transition phenomenon and porosity of these transition metal crystalline complexes were explored.These compounds are all hydrogen bond networks formed by pyridine N and O in water as coordination nodes.Through PXRD test,it is found that Cd(ina)2(H2O)4 loses coordination water and transforms into an amorphous state during heating.The glass transition phenomenon occurs when heated.Powder diffraction proved that the structure of the compound changed to amorphous after losing the coordination water.DSC test found that glass transition occurred when heated to 245?.The sample cooled in the supercooled zone was still amorphous by powder diffraction test.The adsorption experiment proved the porosity of the glassy sample,and the connection retention of the compound bond was confirmed by infrared and Raman.Chapter 3 introduces the functionalized ligand 4,4'-(benzoic[i1,2,5]thiadiazole-4,7-diyl)dibenzoic acid(H2btdb)and 4,7-bis(4-pyridyl)-2,1,3-benzothiadiazole(dbpt)and metal ions of different valences have constructed two cases of rigid net-like cations and neutral multifunctional MOFs,namely [Fe1/3IIFe2/3III(btdb)2(dpbt)2]Cl2/3·3DMF(1)and[Zn2(btdb)2(dpbt)2]·3DMF(2).The two MOFs have similar pore environments,but the frame charges are different.We analyze the stability of the compound by comparing the powder diffraction patterns of the compound under harsh conditions;analyze the porosity and selective adsorption of the compound through the adsorption data of CO2,CH4 and N2,and calculate the the difference in the selective adsorption capacity of the framework for these three gases through IAST.We further compared the differences in the capture behavior of iodine between the two MOFs in the gas phase,the organic phase and the water phase.We found that in the water phase,Fe-MOF can quickly absorb iodine and convert it into I3-,At the same time,the Fe²⁺ of Fe-MOF is partly oxidized to Fe³⁺,thereby enhancing the interaction between the cation framework and the host and guest of the I3-anion to achieve the purpose of encapsulating iodine.In the gas phase and cyclohexane phase,both I2 and I3-exist in the pores of MOF,which shows that water can promote the charge transfer from I2 to Fe²⁺,thereby enhancing the adsorption capacity of MOF to iodine.Finally,the difference in conductivity of the iodine-loaded MOFs was measured,and it was found that the conductivity of the ionic Fe-MOF loaded with iodine was increased by about 105 times,which was much better than that of Zn-MOF.Finally,the mechanism for this phenomenon was explored through the ultraviolet-visible diffuse reflectance spectroscopy.