Construction Of Functional Indium Organic Frameworks With Conjugated Aromatic Carboxylate Ligands For Properties Research

According to the principle of coordination chemistry,indium metal organic frameworks have been investigated in this work focusing on synthesis method,crystal structure,luminescent properties and application as multi-functional materials.15 novel indiummetal organic frameworks have been hydro（solvo） thermally synthesized by varying the main ligands conjugated aromatic carboxylic acids from monocyclic,bicyclic,tricyclic to tetracyclic,and the auxiliary ligands o-phenylenediamine,2,2’-bipyridine and phenanthroline.The compositions and crystalline structures of these metal organic frameworks have been characterized by elemental analysis,single crystal and powder X-ray diffraction.The properties of these compounds are also investigated by TGA,fluorescence spectroscopy,UV-Vis spectroscopy and electrochemical workstation,which further reveal the relationship between structure and property.By choosing furan-2,5-dicarboxylic acid（H₂FDA）as ligand,a novel 3D indium metal organic framework[In（FDA）（HFDA）（H₂O）₄]·2H₂O（1）is achieved,which displays a supramolecular metal organic framework with 6-connected pcu topology driven by hydrogen bonding and π···πstacking.Interestingly,the uncoordinated carbonyl group of 1 can sensitize Ln³⁺ions to obtain Dy³⁺@1 and Eu³⁺@1 materials for enhancing luminescence.When Eu³⁺concentration increased from 0.0 to 1.6μmol/L in aqueous solution,1 exhibits distinguishable luminescence color change from blue to red with fast detection time（<2 min）and the ratio of luminescence intensity at 617 nm to that at 408 nm(I₆₁₇/I₄₀₈)enhances linearly with a low detection limit of 0.87μmol/L.Additionally,careful adjustment of Ln³⁺ions,white-light emission material could be achieved with metal content of Dy_0.87Eu_0.13.In the following research introducing 2-quinolinecarboxylic acid（2-Hqlca）as main ligand and 1,2-diaminobenzene（OPDA）as auxiliary ligand,two indium metal organic frame works formulated as[In（2-Hqlca）₂Cl₃·3H₂O]（2）and{[In（2-QLBM）（2-qlca）Cl₂]₂·CH₃CN·2H₂O}（3）have been synthesized and characterized.2 possesses a（6⁶）dia network with channel diameter about 0.19 nm,and 3 displays a（3,4）-connected topology network with the Schl?fli symbol of（6³）（6⁵·8）,whose channel diameter is about 0.37 nm.Owing to large voids in the framework,3 can serve as a host for reversible encapsulating iodine corresponding to the 1.52 molecules of iodine per formula unit with fast response and high sensitivity.Moreover,absorption spectrum demonstrates the band gap of 3 is 3.58 e V.When adsorbing iodine into framework,the host structure of 3 is relatively perturbed by the presence of guests and exerts a remarkable influence on the band size and gap state.Subsequently by means of adding coordinate sites and extending conjugate system to change experiment conditions,selecting quinoline-2,3-dicarboxylic acid（2,3-H₂qldc）as main ligand,1,10-phenanthrolin（phen）and 2,2′-bipyridine（2,2′-bipy）as auxiliary ligands,eight indium metal organic frameworks formulated as[In₂（phen）₃Cl₆]·CH₃CN（4）,[In₂（phen）₃Cl₆]·CH₃CN·2H₂O（5）,[In₂（phen）₂Cl₆（6）,[In（3-qlc）₂（phen）Cl]（7）,[In（3-qlc）₂（2,2′-bipy）Cl]·2H₂O（8）,[In（3-qlc）₃（phen）]·H₂O（9）[In_0.5K（3-qlc）Cl_1.5（H₂O）_0.5]_2n（10）and[In K（ox）₂（H₂O）₄]_n（11）are obtained.Due to existing hydrogen bonds forming coplanar dimers,7 and 8 show more extendedπ-conjugated system and display obvious aggregation-induced emission properties in the solid state.10 represents the chiral two-fold interpenetrating metal organic framework with right-handed helical chain along the 4₃ screw axis.Encouraged by the UV-visible absorption,10 displays an overall efficiency of 8.07%,which is22.09%higher than that of the device containing only N719（6.61%）.In order to further extend conjugate system,tris-（para-carboxylphenyl） phosphine oxide（H₃TPO）is selected as ligand.Two topological types of{H[In₃（TPO）₂（OH）₄]·2H₂O}n（12）and[In（TPO）]_n（13）are constructed.Increasing node connectivity as well as the trapping of guest OH^–anions,5-fluorouracil（5-FU）is preferentially captured into the 12,which exhibits an outstanding loading capacity around 34.32 wt%.¹⁹F NMR spectroscopy is further employed to investigate host-guest interaction and reveals the binding constant（K_a=3.84×10²L/mol）.Meanwhile,the controlled release of 5-FU in a simulated human body with liquid phosphate-buffered saline solution by bio-friendly Zn²⁺-triggered is realized.With an elevated Zn²⁺concentration,the drug release will be enhanced.Focused on increasing the number of carboxylic acid,1,3,5-tri（4-carboxyphenoxy）benzene is choosen as ligand to construct two metal organic frameworks,[In₂（TCPB）₂]·2H₂O（14）and{[In₃O（TCPB）₂（H₂O）₃]OH}（15）.Yellow crystals 14 undergo humidity-induced structural transformation to yield deep red crystals 15,which could also undergo a reversible transformation into 14 driven by thermal dehydration.Notably,the color of 14 takes only 5 min changed under 58%relative humidity at 298 K,which is much quicker than that of common desiccant bluestone.When increased water content in the range from 0.0%to 0.2%in acetonitrile solvent,14 could rapidly detect trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95×10^-6.In addition,15 displays excellent proton conductivity up to 2.84×10^-4S cm^-1at 298 K and 98% relative humidity.