The Design,Synthesis And Properties Of Metal-organic Cage-based Porous Materials

Metal-organic cages are a class of supramolecular compounds with specific cavities and functions.The design and synthesis of novel multifunctional materials using cage-like compounds as building blocks has attracted considerable attention in the field of coordination chemistry.In recent years,more and more metal-organic cage-based porous materials have been designed,synthesized and applied in adsorption and separation,gas storage,luminescent materials and catalysis.In this project,metal-organic cage was used as the building blocks,which was reasonably designed at the molecular level.Through aldolamine condensation reaction and coordination self-assembly,tetrahedral cage with specific cavity and cubic cage with specific function were used as the building block in the assembly of new multi-functional metal-organic materials.The main research work of this project consists of the following three parts:（1）Zeolite LTA topological porous supramolecule was synthesized based on tetrahedral cages:3,5-bis（bromomethyl）toluene was used as raw material to synthesize 3,5-bis(2-（imidazole-2-formaldehyde）toluene.A tetrahedral metal-organic cage was synthesized by supramolecular coordination self-assembly of 3,5-bis（bromomethyl）toluene,Fe（ClO₄）₂ and（R）-1-phenylethylamine,which was further assembled with tetrahedral anions through weak interactions such as hydrogen bonding and electrostatic interaction to form highly ordered porous supramolecule 1 with LTA topology.X-ray single crystal diffraction analysis revealed that 1 crystallized in the cubic F₂₃ space groups with a giant unit cell volume of 157931（18）?³.The double 4-ring was composed of tetrahedral cage with four adjacent anions and each double 4-ring connected with twoβcages.Double 4-rings andβcages formedαcage with larger cavity through accumulation.The LTA topology structure of 1 with various cavities was capable of capturing small iodine molecules and large dye molecules.Magnetic measurement showed that supramolecule 1 exhibited spin-crossover behavior at room temperature.In addition,the spin-crossover behavior disappeared after guest molecules were encapsulatd into the cavities of 1.（2）Three-dimensional（3D）porous Fe（Ⅱ）metal-organic polymer was constructed with tetrahedral cage as the building blocks:（R）-1-phenylethylamine,Fe（Ⅱ）and 1,6-bis（imidazole-2-formaldehyde）hexane were mixed to assemble tetrahedral compound DQ6.4,4’-diaminodiphenylmethane,Fe（Ⅱ）and or 6-（imidazole-2-formaldehyde）hexane were mixed to assemble spiral compound DX6.Based on the crystal structure analysis of DQ6 and DX6,it is assumed that DQ6 is the central group and DX6 is the intermediate to assemble 3D porous metal-organic polymer.In order to verify the feasibility of the conjecture,spirochaetal complexes DX5 and DQ5 were synthesized from 5-（imidazole-2-formaldehyde）pentene and1,5-bis（imidazole-2-formaldehyde）pentane.According to the crystal structure analysis,DX5and DQ5 should be assembled into 1D chain-like porous metal-organic polymer.Based on this design concept,metal-organic polymers PC5 and PC6 were synthesized from 1,5-bis（imidazole-2-formaldehyde）pentane and 1,6-bis（imidazole-2-formaldehyde）hexane by reacting with 4,4’-diaminodiphenylmethane and Fe（Ⅱ）,respectively.IR and Raman spectra showed that the starting materials were reacted completely.EDX spectra showed that Fe（Ⅱ）ions were successfully coordinated with ligands,which further indicated the successful synthesis of metal-organic polymers PC5 and PC6.X-ray powder diffraction showed that both PC5 and PC6 were long-range disordered structures.The pictures of SEM and TEM showed that PC5 and PC6 were composed of small spheres ranging from hundreds nanometers to micrometers.The stability tests showed that PC5 and PC6 have good thermal and chemical stability.It was found that PC5 and PC6 could recognize iodine,but could not recognize tetrathiafulvalene（TTF）.The iodine encapsulated in the channels of PC5 and PC6 provided the action sites for the adsorption of TTF due to the charge transfer effect between iodine and TTF,promoting the encapsulation of TTF.The solid adsorbent can be reused by desorption with methanol solvent.（3）Directional assembly of fluorescent Zn（Ⅱ）metal-organic polymers based on cubic cages with fluorescent properties:On the basis of cubic cages structure analysis,the mononuclear Zn（Ⅱ）complexe with fluorescent properties was synthesized from 5,5’-diamino-2,2’-bipyridine with richπelectrons.The Zn（Ⅱ）complexe was further reacted with linear ligands terephthalaldehyde and 1,4-biphthalaldehyde to obtain metal-organic polymers ZnSQ and ZnDQ.IR and solid-state NMR spectra showed that the starting materials reacted completely.EDX spectra showed that Zn（Ⅱ）ions were successfully coordinated with ligands and the metal-organic polymers ZnSQ and ZnDQ were successfully synthesized.X-ray powder diffraction showed that both ZnSQ and ZnDQ have good crystallinity.The pictures of SEM and TEM showed that both ZnSQ and ZnDQ were amorphous layered morphology.The excitation wavelengths range of ZnSQ and ZnDQ were determined by solid UV-Vis spectra.The fluorescence spectra showed that both ZnSQ and ZnDQ had fluorescence properties and could recognize the nitro groups in aromatic ring.