Metal Organic Frameworks Based On Cyclotriphosphazene-Functionalized Hexacarboxylate Ligands Bearing Different Substituents:Synthesis And Characterization,Structure Modulation,and Properties

Metal-organic frameworks(MOFs also referred to as porous coordination polymers)are formed by bridging metal ions or clusters with organic ligands.The past two decades have witnessed their rapid development.As a new kind of functional materials,MOFs have drawn much attention from academic and industrial community.Because MOFs combines the features of both inorganic compounds and organic polymers,they not only possess rich structures,but also have larger specific surface areas and pore volumes as well as higher porosity as compared to traditional porous materials.It has the characteristics of design ability,scalability and easy functionalization.It has shown good application prospects in various fields such as gas storage,separation,selective catalysis,fluorescence,drug delivery and chiral resolution.In this paper,based on the crystal engineering,starting from the functional properties of the materials,the hexacarboxylate ligands with cyclotriphosphazene as the scaffold were selected for functional group modification,and the effect of functional groups on the structures of the synthesized materials was explored to further optimize the properties of the materials.In this paper,solvothermal method was used to react with different metal ions to construct a plurality of MOFs.The basic characteristics of the samples were infrared and thermogravimetry,and the gas adsorption and separation properties and fluorescence properties of the materials were investigated.1.Hexakis(4-carboxyphenoxy)cyclotriphosphazene was selected as a prototypical ligand,which was modified at the ortho and meta positions of the carboxylate groups with functional groups bearing different sizes and electronic natures(-OCH3,-CH3,-Cl,-Br,and-I).Their structures were characterized by spectroscopic techniques such as 1H NMR,13C NMR and FTIR.2.Four Ho3+-based MOFs with different structures were synthesized by a solvothermal method using the ligands H6L1,H6L2,HeL4 and H6L6 as ligands,respectively.The MOF materials were analyzed by single-crystal X-ray diffraction and conventional FTIR and TGA.Furthermore,the gas adsorption properties of one of four compounds were examined.3.Four Cd2+-based MOFs with distinctly different structures were synthesized by the solvothermal method using the H6L1,H6L2,H6L3 and H6L5 as ligands,respectively.They were fully characterized by FTIR and TGA as well as single-crystal X-ray diffraction.4.A MOF was prepared via a solvothermal reaction of the organic ligand H6L1 and the main group heavy metal ion Pb2+.The resulting MOF was fully characterized by conventional FTIR,TGA and single-crystal X-ray diffraction.The gas adsorption properties with respect to C1-C2 hydrocarbons and carbon dioxide were systematically investigated.