Study On Synthesis And Properties Of Metal-organic Frameworks Based On Novel 1,2,3-trisubstituted Phenyl Ligands

Metal organic materials(MOMs)are periodic network structures formed by inorganic metal nodes and organic ligands through coordination bonds.Usually,metal nodes serve as vertices and organic ligands serve as connecting edges,which eventually expand from supramolecular one-dimensional metal organic polyhedron to two-dimensional and three-dimensional polyhedron porous coordination polymers.Because of its highly crystalline and adjustable properties,MOM has attracted much attention in the field of solid-state chemistry and material science.In the traditional research,the organic linker with rigid structure has been explored.The benzene ring is widely used in the design and application as the organic linker because of its simple modification and high structural rigidity.In many designs of core skeleton using benzene ring,organic linkers with high symmetry are applied to synthesize crystalline materials with orderly orientation.In many reports of bi-aryl benzene system,the A-1,3-H interactions between diphenyl rings could result in conformational distortion between benzene rings.Driven by dihedral angles,many highly symmetrical 1,3,5-trisubstituted phenyl,1,2,4,5-tetrasubstituted phenyl and all aryl hexa-phenyl substituted organic linkers have been developed.Throughout the ligand design process of metal organic frameworks(MOFs),low symmetry 1,2,3-trisubstituted phenyl ligands have not been reported so far.The research shows that for organic linkers with rigid structure,it is easy to form crystalline framework materials with low stability due to the low degree of symmetry.The design of new 1,2,3-Trisubstituted phenyl organic linkers from the perspective of improved symmetry is very important.Therefore,a new class of low symmetric 1,2,3-Trisubstituted phenyl ligands were designed and synthesized for the first time.They were applied for the synthesis of a new class of MOFs materials with metal ion bonding.The main innovation points of this paper are as follows:(1)With A-1,3-H interaction,horizontal and vertical coordination bonding sites was designed and introduced into the low symmetry ligand 1,2,3-trisubstituted phenyl to cross-link the skeleton in three-dimensional space and expand the network.Four low symmetric 1,2,3-Trisubstituted phenyl organic linkers with horizontal and vertical coordination directions were synthesized for the first time.The structure and morphology of such humanoid orthogonal twisted arm(OTA)ligands were confirmed by single crystal structure.Then,we used OTA ligands to bind with metal ion clusters(Cd²⁺,Cu²⁺)to prepare three highly crystalline MOFs materials(OTA1-MOF-Cd,OTA2-MOF-Cd,OTA2-MOF-Cu).It is found that in space,humanoid OTA ligands expand the skeleton through orthogonal coordination of hands and feet,which improve the chemical stability of the skeleton through metal ion replacement.OTA2-MOF-Cu is composed of hexagonal repeating unit cells with methyl pointing to the center of the pore.The structure is simplified to a new topological structure(4,4,4-c).The performance test and characterization at 298 K showed that the CO₂ adsorption value was 10.76 cm³ g^-1 with good selective adsorption performance of CO₂/CH₄(the adsorption ratio=2).OTA2-MOF-Cu has excellent catalytic activity(58-100%yields)in the cyclic carbonate conversion experiment of CO₂.After five cycles of recycling,it maintained the catalytic performance.OTA2-MOF-Cu has excellent application value in the research of CO₂capture and reuse,which provides a practical foundation for the synthesis of new low symmetrical 1,2,3-trisubstituted phenyl linkers in MOFs.(2)Ligands 6a-6c with inverse orthogonal twist arms were designed and synthesized for the first time.The concave coordination site of 6a's concave body is repulsed by the benzene rings.The carboxylic acid breaks the internal chelation binding mode in space,expands the skeleton with Cd²⁺ion cluster in two-dimensional space,and a new two-dimensional MOF skeleton(6a-MOF-Cd)is synthesized with helical structure.The material is stable in common organic solvents for 1 week with its good acid-base resistance(p H=2-12)in the aqueous solution.In addition,the skeleton shows good adsorption performance in CO₂ capture.This novel concave 1,2,3-trisubstituted phenyl linker was used to prepare helical two-dimensional MOF framework materials for the first time,which provides a practical research guidance value for the development and application of MOFs ligands.(3)The concave convex ligand L₁ substituted by meta benzoic acid was designed and synthesized.The ligand showed high center symmetry due to the combination of aromatic repulsion and torsion force.After binding with metal(Co²⁺,Cd²⁺)ion clusters,the ligand extends the skeleton in one or three dimensions.The one-dimensional polymer,L₁-Polymer-Co,was extended via backbone hydrogen bonds.Through the coordination and chelation between L₁ and Cd²⁺,the metal oxygen SBU structural unit was constructed,and a three-dimensional small pore crystallization framework(L₁-Polymer-Co)with a new topology was prepared.The framework topology was named kai topology.In addition,USF-KZ-1 with excellent resistance to acid-base aqueous solution(p H=2-11)can exist stably in common organic solvents for half a year.Through the study of 1,2,3-trisubstituted phenyl small molecular skeleton,the study provides the reliable analysis for the subsequent derivative application of ligands with low symmetry and gives theoretical guidance for the study of this structure in metal organic framework,covalent organic framework(limited structure and infinite structure)and graphene like ligands.