Construction And Characteristic Of Crystalline Porous Frameworks Based On B←N Dative Bond

The establishment of reticular chemistry has greatly expanded the field of porous materials and revolutionized solid-state materials chemistry.In reticular chemistry,materials can be designed rationally,and their properties can be tailored by designing their structures.For crystalline porous materials,establishing permanent porosity is crucial for their further development.Metal-organic frameworks（MOFs）,covalent organic frameworks（COFs）,and hydrogen-bonded organic frameworks（HOFs）have been widely used in gas storage,gas separation,catalysis,molecular recognition and sensing,energy,environmental science,and biomedicine after the establishment of permanent porosity.Supramolecular crystalline compounds（boron-nitride frameworks,we termed BNFs）constructed by dative boron-nitrogen bonds as nodes have been widely reported.Since they have medium bond energy（about 50-150k J/mol）and reversible formation/breaking properties,it is feasible to construct porous crystalline polymers by coordinating boron-nitrogen bonds as nodes,and new assembly methods are expected to bring unique properties.However,research on porous crystalline polymers constructed by coordinating boron-nitrogen bonds as nodes is still in its infancy,and permanent porosity has not been established yet.Compared with other porous crystalline materials,there are also few studies on the regulation and performance of such compounds.Therefore,this thesis selects pyridine-based organic ligands,prepares a series of boron nitride framework materials through different synthesis strategies,and explores their gas adsorption properties and photo-excited response properties.The research work of this thesis provides theoretical basis and new research ideas for the application of BNFs materials in gas separation and the construction of temperature-light responsive BNFs materials.1.The first stable BNF with permanent porosity,BNF-1,has been constructed,and the single-crystal X-ray structures of synthesized BNF-1 and activated BNF-1a have been characterized clearly.The two-dimensional framework sheets of BNF-1 are interlocked to generate stable crystalline frameworks,and the BET surface area is 255m²/g.This compound has high chemical stability,can achieve gram-scale synthesis,and is easy to regenerate by recrystallization.Gas adsorption experiments show that the material absorbs more acetylene molecules than carbon dioxide molecules.Gas dynamic breakthrough experiments demonstrate its ability to separate C₂H₂/CO₂mixtures under ambient conditions.2.BNF-1F,an isomorphic compound of BNF-1,has been constructed through boronic acid monomer fluorination,and they exhibit different acetylene and carbon dioxide separation capabilities.The structural characteristics,electronegativity effects on framework stability,and the effects on the selective adsorption and separation of acetylene and carbon dioxide mixtures have been systematically investigated.The adsorption mechanism was explored by guest-loaded single-crystal X-ray diffraction and molecular modeling and DFT calculations.The results show that the spatial electrostatic potential（ESP）on the framework pore walls matches acetylene molecules,which is the basis for the molecular recognition mechanism of acetylene molecules binding to carbon dioxide molecules.The relationship between gas adsorption and structure has been established in BNFs for the first time.3.A pair of conformational isomers,BNF-2 and BNF-3,were successfully prepared by regulating the reaction temperature.BNF-3 was assembled by multiple weak interactions within the molecule,while BNF-2 only had weak interchain hydrogen bonds.The different weak interactions in their structures resulted in their different fluorescence temperature response properties.BNF-2 exhibited significantly enhanced fluorescence at low temperatures,accompanied by structural changes.The mechanism of structural changes was explored through in situ excitation single-crystal X-ray diffraction and molecular modeling,temperature-dependent fluorescence excitation-emission spectra,and DFT calculations.The experiments showed that multiple weak interactions in the solid state synergistically contributed to the emission of structural stimuli.