The Syntheses And Properties Of Multifunctional Metal-Organic Frameworks Based On V-Type Carboxylic Acid And Nitrogen Heterocyclic Ligands

Metal-organic frameworks(MOFs)constructed by the coordination of metal ions or metal clusters with organic ligands have attracted the attention of many scientists due to their adjustable porous structure and high porosity,as well as their wide applications in gas adsorption and separation,fluorescence sensing,energy storage and conversion,molecular based magnets,and so on.Compared with porous MOFs constructed by single ligand,the MOFs materials prepared by mixed-ligand strategy combining nitrogen heterocyclic ligands and carboxylic acid ligands with different configurations have the following advantages:1.The multiple functional groups can be introduced into the frameworks;2.On the premise of maintaining the integrity of the whole framework,some ligands can be lost to produce structural defects;3.Multifunctional porous materials with two complementary or contradictory properties can be prepared.Considering the advantages of mixed-ligand strategy for preparing MOFs materials,we selected V-type 4,4'-dicarboxyl diphenyl ether(H2OBA)carboxylic acid ligands and nitrogen heterocyclic ligands with different configurations to construct a series of functional MOFs materials with employing different central metal ions.According to the structural characteristics,we explored the potential applications of these materials in the field of fluorescence detection,adsorption,luminescence,energy storage,and so on.The main contents of this paper are as follows:(1)Through using the ligand H2OBA and auxiliary nitrogen heterocyclic ligand PTD containing conjugated?electron system,a stable luminescent Zn-MOF[Zn2(OBA)2(PTD).2DMF.2H2O]n(compound 1)and an isostructural Co-MOF[Co2(OBA)2(PTD).3DMF.CH3CH2OH.5H2O]n(compound 2)have been synthesized,which display the 3D three-fold interpenetrated frameworks.Compound 1 performs highly thermal and chemical stabilities.Meanwhile,compound 1 exhibits a strong luminescent emission,and can selectively detect Cu²⁺and Cr2O7^2-by luminescent quenching.Furthermore,the explorations of lanthanide cation(Ln³⁺)encapsulation for compound 1 have implied that the emission color of Ln³⁺-doped compounds can cover the whole visible region,showing the potential applications as the emission color and barcoded materials.Moreover,by soaking this MOF into DMF solution containing Ln³⁺ions(Eu³⁺/Tb³⁺,13/7),white light-emission of Ln³⁺-doped compound 1 was realized.Besides,compound 2 exhibits not only high uptake capacity for CO2 molecules with an estimated high sorption heat but also a significant selective adsorption of CO2 over CH4.(2)On the basis of the ligand combination of system(1),we further optimized the synthesis conditions.Here,a porous cobalt-organic framework with pillared layer structures,namely[Co3(OBA)3(PTD)(H2O)2.2DMA.H2O]n(compound 3),was fabricated by cobalt-trinuclear nodes.Compound 3 exhibits a high efficient solvatochromism towards CH2Cl2 within one minute and can sense 200 times at least.The CH2Cl2,CHCl3 and CCl4can be easily distinguished when compound 3 was immersed into the corresponding solvent,respectively.For practical application,the corresponding dropper detector was assembled by employing compound 3 as a sensor for detecting CH2Cl2.Meanwhile,the porous Co3O4was obtained by a simple but effective annealing treatment.Electrochemical measurements confirm that this Co3O4 material derived from compound 3 shows high and stable lithium storage capabilities(1081.75 m Ah g^-1 at 200 m A g^-1 after 115 cycles)and excellent rate properties.(3)On the basis of the above two systems,the linear bidentate nitrogen heterocyclic ligand PTD was replaced by the V-type bidentate nitrogen heterocyclic ligand L1.Using this new ligand combination,a new luminescent compound with 1D microporous channels,namely[Cd(OBA)(L1).0.75DMA]n(compound 4),has been constructed,which features a good thermal and chemical stability.The activated compound 4 with 10.2?channels reveals a positive CO2 uptake capacity at 273 and 298 K,respectively,but it captures a relatively lower amount of CH4 gas under similar atmosphere.Meanwhile,the high H2capture amount of compound 4 has been demonstrated with 165.2 cm³ g^-1 at 1 atm,77 K.Interestingly,this compound displays a prominently selective and sensitive detection to Cr³⁺,CrO₄^2-,and Cr₂O₇^2-in aqueous media.The detection limits of Cr³⁺,CrO₄^2-,and Cr₂O₇^2-are calculated to be 10.25,0.30,and 9.18?M,respectively.The test paper incorporated compound 4 can easily detect these three ions.(4)On the basis of system(3),two isostructural MOFs[(CH3)2NH2]6[M6(OBA)6(L1)3(SO4)2].SO4.x(solvent)(M:Zn for 5,Co for 6)were synthesized by using Zn SO4.7H2O and Co SO4.7H2O,respectively.Interestingly,the anion SO4^2-connects three metal centers to form tri-metal node[M3(SO4)(COO)6]as a secondary building unit(SBU).Then the SBUs are further linked to each other by OBA^2-and L1ligands,obtaining a 2D interpenetrated tripillared-bilayer.Compound 5 is highly stable in water and different organic solvents.Furthermore,compound 5 is the first example luminescent MOF that can simultaneously sense Ni²⁺and PO4^3-with high selectivity and relatively low detection limits of 0.46 and 6.5?M.(5)In order to further expand the richness of the structures,we emploied the symmetrical tridentate heterocyclic ligand L2 instead of the bidentate nitrogen heterocyclic ligand.Herein,we designed and fabricated a porous Zn-based MOF[Zn(OBA)2(L2).2DMA]n(compound 7).The as-synthesized compound 7 is stable in different boiling organic solvents and water solutions with a wide p H range of 2-12,and exhibits intense luminescence emission at 360 nm under excitation of 290 nm UV-light.Significantly,compound 7 shows a high selectivity to detect Fe³⁺,CrO₄^2-,and Cr₂O₇^2-in aqueous solution even under the interference of other ions.Compound 7 can quickly sense these ions in a short time and has a striking sensitivity towards Fe³⁺with ultra-low limits of detection of 1.06?M.Meanwhile,compound 7 can be reused to detect Fe³⁺,CrO₄^2-,and Cr2O7^2-for six times by simple regeneration.Considering the practicability,the mixed matrix membrane(MMM)incorporated compound 7 and poly(methyl methacrylate)has been accessibly constructed.This MMM displays quick detection of Fe³⁺,CrO4^2-,and Cr2O7^2-and prompt regeneration by lifting from analyte.