Syntheses,Structures And Sensing Performance Of Metal-Organic Frameworks

Metal-organic framworks(MOFs),a kind of organic-inorganic hybrid crystalline materials formed by single metal cation or metal clusters with organic ligands of multiple binding sites,exhibit unique chemical and physical properties such as strong luminescent emission,long lifetime,high quantum yield,large specific surface area and good porosity.MOFs have been made to develop attractive applications in wide areas such as heterogeneous catalysis,gas separation and storage,sensing,magnetism,biomedical imaging and drug delivery.In this thesis,based on 1,1?:4?,1?-terphenyl-2?,4,4?,5?-tetracarboxylic acid(H4L1)and a newly synthesized ligand 9-(Pyridin-4-yl)-9H-carbazole-3,6-dicarboxylic acid(H2L2)and a variety of rare earth metal ions and transition metal ions,we synthesized five novel metal-organic complexes under the solvothermal condition.The structures and phase purities of the complexes were analyzed and verified by single crystal X-ray diffraction,elemental analysis,powder X-ray diffraction and 1H,13 C NMR spectra.The thermal stability and fluorescence properties of complexes were characterized and analyzed by fluorescence spectra,FTIR,thermogravimetric analysis and UV absorption.The potential applications of these complexes in the sensing of nitro compounds and metal ions have also been investigated.The following three aspects are the main research results of this thesis:1.Three isostructural three-dimensional(3D)lanthanide-based metal-organic frameworks [Ln2L1(H2L1)(NMP)2]·H2O(Ln = Sm(1),Eu(2),Gd(3),NMP = N-methyl-2-pyrrolidone)have been synthesized and structurally characterized.In 1-3,two Ln3+ ions are doubly-bridged by two oxygen atoms of two carboxylate groups to form the dinuclear Ln2(OCOO-)2 unit.Each Ln2(OCOO-)2 unit links with four H2L12-ligands and four L14-ligands to lead to the 3D framework,which can be rationalized as a new trinodal 4,4,8-connected topological network with a Schl?fli symbol of(44.62)(45.6)(412.616)by considering the dinuclear Ln2(OCOO-)2 units as 8-connected nodes and L14-/H2L12-ligands as planar 4-connected nodes,respectively.1 and 3 exhibit blue emission originated from the ligand with the emission maximum at 384 nm,while 2 shows intense characteristic red emission of Eu3+ ions and weak ligand-centered emission.Moreover,2 has fluorescent quenching response towards the aromatic nitro explosives,especially for the 3,4-dinitrotoluene(3,4-DNT)with the linear Stern-Volmer relationship in the concentration range of 0 ~ 1m M and the quenching constant(Ksv)of 2.084 × 103 M-1.2.A two-dimensional(2D)metal-organic framework(MOF)formulated as [Cd2(?3-L2)2(DMF)4]·H2O(4)was synthesized under solvothermal condition.Crystal structural analysis reveals that 4 features the layered 2D framework with L22-ligands as 3-connected nodes.The compound 4 emits blue-violet light with the narrow emission peak and the emission maximum at 414 nm upon excitation at the maximum excitation wavelength of 340 nm.The compound 4 has a similar emission spectrum curve to the free H2L2 ligand that indicates the emission of compound 4 should be originated from the coordinated L22-ligands.3.A 3D metal-organic framework(MOF)Zn L2·0.5H2O·0.75DMF(5)has been synthesized under solvothermal condition.Crystal structure analysis shows that,in 5,each dinuclear Zn2(COO)2 unit is doubly-bridged to the other two by the carbazole moieties to form the 1D chains,which are further connected together by pyridine moieties to lead to the 3D framework.5 exhibits both high structural stability and good luminescent stability in water with the p H range of 4 ~ 10.5 displays the luminescent quenching response for Fe3+ in water with good linear correlation between the quenching efficiency and the concentration with Ksv of 10800 M-1 in the low concentration range of 0 ~ 0.1 m M.Interestingly,it is observed that the sensing performance for Fe3+ is stable in the p H range of 4 ~ 9,enabling 5 to detect Fe3+ ions in weak acidic and weak basic solutions.