From Schiff-base Macrocycles To Porous Organic Cages(POCS)and To Covalent Organic Frameworks(COFs): Design,synthesis And Application

In the past decade there has been tremendous interest in the development of organic porous materials due to their great potential in gas storage/separation and catalysis applications.These purely organicbased porous materials are constructed through covalent bonds and usually exhibit high chemical and thermal stability.A variety of chemical reactions have been utilized to construct organic porous materials,among which Schiff-base chemistry has been one of the most frequently used approaches.Since such chemistry doesn't require expensive transition metal catalysts and also has“self-correction”capability under thermodynamic control,it has been widely utilized in materials development.Typically,organic porous materials can be classified into two groups:porous organic molecular cages and porous organic networks.Porous organic networks also includes covalent organic frameworks(COFs)and porous organic polymers.In our work,we constructed Schiff base macrocycles,porous organic cages(POCs)and covalent organic frameworks(COFs)based on Schiff base chemistry.Sciff base macryclic complexes:Schiff-base macrocycles as one of the most important fields in macrocyclic and supramolecular chemistry,especially Salen-metal complexes,have attracted continuously increasing attention,because some interesting weak interactions have been found such as hydrogen bonding,hydrophohic,?-?stacking,and cation-? interactions.With regard to the cation-? interactions,they have been widely observed in several fields like chemistry,material science,biology.In the second section,we have synthesed a series of Schiff base macrycyclic complexes via substitution(NO3-replaced by N3-),and whether Na(1)occupies the unsaturated coordination site depends on the pH value of system.A new Na-?(N3-)interaction is comfirmed by Crystallographic analysis,FT-IR spectra and simulations.In the thired section,we have determined three Schiff base macrocyclic complexes using a pre-organized intermediate via UV-Vis titration technology and reasonable hypothesis.Porous organic cages:herein,we have adopted the concept of 'cage to frameworks'to successfully produce a soluble Na-N connected coordination networked cage Na-NCl by using a[3+6]porous imine-linked organic cage NCI as the precursor.Nevertheless,an alternative synthetic strategy is adopted by using a rigid imine cage building block instead of the flexible reduced amine form.X-ray single-crystal diffraction analyses of NCI and Na-NCl confirm the achievement of our synthetic strategy from a rigid discrete molecular cage to a networked cage and the latter posses hierarchical porosity(both inherent voids and interconnected channel).More importantly,gas sorption experiments of Na-NCl exhibit significantly enhanced capacity toward CO2 at high pressure in comparison with that of NCI and remarkably low CO2 adsorption enthalpy for Na-NCl.Porous organic cages and covalent organic frameworks:The aim of this work is to explore more strategies for the growth of highly crystalline porous organic cages(POCs)and even covalent organic frameworks(COFs)with the imine linkage,especially in the case that highly crystalline form is hard to be obtained via the conventional method.Herein we have developed a facile and efficient approach for growing four highly crystalline POCs and even one COF.Unlike the conventional organic solvents/acid catalyst system,we adopt H20/EtOH/MOH(M = Na,K,Cs)as the reaction media,which leads to the facile formation of POCs and COFs with high crystallinity.It is found that the introduction of a large amount of water(up to 50%)in our case is believed to facilitate the crystallization process for high-quality POCs and COF in addition to serving as a good solvent for precursors.According to this study,we have shown the importance of water in the crystallization process of imine based materials,also including the formation of alkali metal phenoxides in our case.Furthermore,the generality and transferability of this approach are demonstrated by successfully growing high-quality crystals of four POCs and one COF.This versatile synthetic method is believed to provide a powerful tool for the exploration of more POCs,COFs and even some other phenol-based materials.