Assembly Of Metal Organic Frameworks Based On 4-connected 3,3',5,5'-azobenzenetetracarboxylic Acid:Structures,Magnetic Properties, And Photoluminescences

According to the topology of structures,metal organic frameworks can be divided into one-dimensional chains,two-dimensional layers and three-dimensional skeleton.Due to their unique structures,large specific surface area,and varieties of coordination modes,they can be widely used in the fields of gas adsorption and separation,chemical sensing,and magnetism.However,how to design and synthesize a crystal with the desired structure and function is still a challenge.The choice of ligands is particularly important.In this thesis,we selected a symmetric aromatic tetracarboxylic acid,3,3',5,5'-azobenzenetetracarboxylic acid?H₄abtc?as organic ligand,which has main characteristics as following.First,it is a highly symmetrical long rigid ligand,which is conducive to the stability of the nodes and the skeleton;Second,it has four carboxylic acid groups,which can be partially or completely deprotonated and then links to the metal centers in a variety of coordination modes?monodentate,multidentate,and chelated?;Third,it contains a conjugated?system with aromatic groups,which can combine 3d or 4f center ions to construct compounds possessing magnetic or luminescence properties.By self-assembly of H₄abtc ligands with different 3d and 4f metal ions,seven compounds were synthesized.We discussed the impact factors of the structures in detail,including the types of metal ions and solvents.In addition,we have investigated their gas adsorption and separation,metal ion sensing and magnetic properties according to their structural characteristics.This paper mainly includes the following two parts:?1?Three metal-organicframeworks,{[Co₂(ao_0.34btc)?DMF?₃]·3DMF}_n?1?,{?Me₂NH₂?₂[Mn₁₂?OH?₄?abtc?₆?DMA?₆?H₂O?₆][Mn?H₂O?₄]·36H₂O}_n?2?,and{[Zn₃?abtc?_1.5?H₂O?_2.5?DMA?_0.5]·5DMA·2CH₃OH}_n?3?,have been successfully designed and synthesized by using H₄abtc ligand and different transition metal ions under solvothermal condition.In complex 1,the ao_0.34btc^4-ligands connect[Co₂?CO₂?₄]second building units?SBUs?to generate a three dimensional?3D?crystal structure,showing the PtS-type topology.The[Mn₃OH?CO₂?₆]SBUs connected by abtc^4-produce the 3D soc-type cage in complex 2.While complex 3 consists of two categories of[Zn₂?CO₂?₄]SBUs,resulting in the NbO-type cage with the assistance of the abtc^4-ligands.Magnetic measurements reveal antiferromagnetic exchange interactions exist in complexes 1 and 2.Besides,the luminescence investigations of complex 3 show its excellent sensing ability of Fe³⁺ions by fluorescence quenching.?2?We used the H₄abtc ligand to react with different rare earth metal ions solvothermally,preparingfourisomorphic2Dcompounds4-7successfully,whichare Ln₂?abtc??DMF?₅?NO₃?₂·DMF(Ln=Tb³⁺,Eu³⁺,Gd³⁺,Sm³⁺).In 4-7,two crystallographically independent Ln³⁺are linked by abtc^4-ligand to form a dinuclear cluster,then each cluster is linked by four abtc^4-ligands,forming a?4,4?-connected sql-type topology.The magnetic data of 6 indicate there is an antiferromagnetic interaction between adjacent Gd³⁺ions.Therefore,employing the H₄abtc ligand with the paramagnetic Co²⁺ion and Mn²⁺ion,3D structures with the PtS and soc topology can be obtained,respectively.The antiferromagnetic interactions exist between the paramagnetic ions.While the H₄abtc ligand coordinates with the 3d¹⁰ Zn²⁺ion forming NbO type cage,which shows excellent ability for sensing Fe³⁺ions.The H₄abtc ligand binds to different rare earth metal ions,constructing a2D network structure with the sql topology type.The complex containg Gd³⁺exhibits antiferromagnetic property.Using H₄abtc ligands connecting different 3d or 4f metal ions can construct MOFs with different structures and properties.