Synthesis And Properties Of MOFs Induced By Chiral Solvent

Metal organic framework materials（MOFs）are a class of porous materials that combine metal and organic ligands with the advantages of tunable structure,large pore size and versatility.As a branch of the MOFs family,chiral metal-organic framework materials（CMOFs）are often used as an efficient fluorescent sensor for chiral recognition and chiral separation processes.In this paper,different metal and non-chiral ligands were self-assembled by a solvothermal method under the induction of the chiral solvents S-propanediol and R-propanediol,forming CMOFs with different structures and showing good recognition ability for different chiral substrates.The paper is divided into three main parts as follows:1.The chiral enantiomeric CMOFs[K₂（H₃TCA）₄（OH）₂（H₂O）₂]（1-S）and[K₂（H₃TCA）₄（OH）₂（H₂O）₂]（1-R）were synthesized in the chiral solvents S-propanediol（S-pd）and R-propanediol（R-pd）,respectively,using 4,4’,4’’-triphenylamine（H₃TCA）and KOH as raw materials.1-S and1-R are structurallyin mirror symmetry and both crystallise in the chiral orthogonal space group I222.The two K⁺ions form a[K₂O₄]binuclear unit by sharing four oxygen atoms,which are then bridged by TCA ligands to form a helical structure.Each of helical structure is then connected to each other by TCA ligands and extended into three dimensions to form a porous three-dimensional framework.In this case,1-S exhibits a left-handed helical structure while 1-R is a right-handed helical structure,and the opposite CD spectra also demonstrate the nature of their mutual chiral enantiomers.1-S and 1-R were applied to identify the chiral substrates S-/R-pd and D-/L-camphor（D-/L-cam）,and the enantioselective recognition of the chiral substrates were determined by comparing the percentage change in fluorescence of the CMOFs.The experimental results showed that the percentage change in fluorescence of 1-S to S-/R-pd was 1.07,while that of 1-R to S-/R-pd was 0.57;in addition,the percentage change in fluorescence of 1-S to D-/L-cam was found to be 1.30 and that of 1-R to D-/L-cam was 0.77.The different fluorescence responses of 1-S and 1-R indicate that both can be used as fluorescent sensors to achieve enantioselective recognition of S-/R-pd and D-/L-cam.2.A pair of chiral enantiomeric 3D CMOFs[Tb₂FDA₃（S-Pd）₂]（2-S）and[Tb₂FDA₃（R-Pd）₂]（2-R）were synthesized from 2,5-furandicarboxylic acid（H₂FDA）and Tb（NO₃）₃·6H₂O,respectively,in the chiral solvent S-/R-propanediol（S-/R-pd）.Aim to explore the chiral origin,the non-chiral[Tb IPA_1.5（S-pd）]（3）was synthesised under the similar conditions using isophthalic acid（H₂IPA）ligand instead of H₂FDA.The crystal structures show that 2-S and 2-R crystallise in the chiral orthogonal space group P2₁,while 3 crystallises in the monoclinic orthogonal space group C2/c.The reason for the creation of the chiral helix was analysed by structural comparison and the presence of a dihedral angle of 22.793°between adjacent ligands in 2-S and 2-R was key to the creation of chirality.In fluorescence sensing experiments,enantioselective recognition of cinchonine and cinchonidine was demonstrated by comparing the K_svconstants of 2-S and 2-R for cinchonine and cinchonidine,where the quenching ratios of cinchonine and cinchonidine were 0.81 for 2-S and1.43 for 2-R.In addition,by doping Eu³⁺into 2-S,the emission fluorescence color was changed from green to red.The change in fluorescence lifetime at ⁵D₄ indicates an effective energy transfer from Tb³⁺to Eu³⁺.3.Three metal-organic framework materials were synthesized using2,5-furandicarboxylic acid（H₂FDA）and 6,6’-dimethyl-2,2’-bipyridine（DMBP）,namely the chiral[Zn（FDA）（DMBP）]（4-S）,[Zn（FDA）（DMBP）]（4-R）and the non-chiral[Zn（FDA）（DMBP）]（4-rac）.4-S and 4-R both crystallize in the chiral orthogonal space group P2₁,where alternating linkages of FDA^2-ligands and metal atoms form one-dimensional helical chains.4-S is a right-handed structure,but 4-R is a left-handed structure.The non-chiral 4-rac crystallises in the monoclinic crystal system P2₁/c and has a similar one-dimensional helical chain to 4-S and 4-R.However,the two adjacent helical chains exhibit opposite helical orientations,leading to the ablation of 4-rac and ultimately to the creation of a non-chiral framework.It was subsequently demonstrated by fluorescence sensing experiments that 4-S and 4-R can be used as a chiral fluorescence sensor for selective recognition of D-/L-phenylalanine（D-/L-Phe）.The quenching ratio of 0.88 for D-/L-Phe to 4-S and 1.45 for 4-R was obtained.