Metal-Organic Frameworks Based On Low Symmetric Penta-/Hexa-Carboxylate Ligands:Synthese And Properties Investigation

Recently Metal-Organic Frameworks(MOFs)have attracted considerable interest due to their versatile structural and potential applications.MOFs based on symmetric carboxylate ligands have been extensively investigated,in contrast MOFs based on low symmetric carboxylate ligands were much less concerned.The use of low symmetric aromatic carboxylate licgands for the construction of MOFs has been shovwn to be an effective way to suppress framework interpenetration and promote the formation of highly porous materials,which is important for the sensing and detecting of large size guest molecules.Up to now a few MOFs have been employed to detect Nitroaromatic compounds(NACs),however,the using of MOFs to detect dinoseb,an important polymerization inhibitor in petrochemical industries and a pesticide in agriculture,was not reported.In this dissertation,9 new MOFs were prepared through five low symmetric penta-or hexa-carboxylate ligands(H5L1,H5L2,H6L3,H6L4 and H6L5,among which H6L3 and H6L4 are new ligands).Then the emission modification of some MOFs were realized through loading of photoluminescent[(ppy)Pt(MeCN)2]+([Pt]+)into their channels.Furthermore,the detecting behaviors of the MOFs and the composites toward NACs,especially dinoseb were investigated.(1)Synthesis of MOFs.Nine new MOFs were prepared through the reactions of the ligands and metal ions.Their structures were established by single crystal X-Ray analysis.Furthermore,the compounds were characterized by TGA,N2 sorption and luminescent analysis.Compounds 1 and 2(reported compound)were synthesized by the reactions of H5L1 and Zn2+ through "4+(3+2)" assemble strategy.They are the first two zeolitic abiu} MOFs which are built of a same pentacarboxylate ligand and metal ion but have two configurations and channel shapes(distorted herringbone-and honeycomb-shaped channels for 1 and 2 respectively).They can demonstrate interesting ’"breathing effects"(reversible/irreversible structural transformations)through a crystalline intermediate 3.The reaction of H5L2 and Cd2+led to 4 that exhibits {Cd8(L2)4} SBB with a elliptical cylinder shape.Each SBB is used as a 10-connected node for the construction of bet framework.5 was obtained by the reaction of H6L3 and Cd2+.It exhibits(4,4,4)-connected network with new topology.The corresponding Schlafli symbol is {42;6;83}3{42;63;8}.6 was synthesized by the reaction of H6L4 and Zn2+.It exhibits bct topology based on 10-connected calixarene shape {Zn8(L4)4} SBB.6 represents the first attempt of using quasi-calixarene shape SBBs to construct MOFs.The assembly of H6L5 and Ca2+/Mg2+ led to isomorous 7 and 8 respectively.Their frameworks have dia topology and are based on 4-connected truncated tetrahedron {M12(L5)4}(M=Ca/Mg)SBBs.Compound 9 was obtained by the reaction of H6L5 and Pb2+.The compound displays a(5,5)-connected nia-5 topology and the Pb2+ ions adopt either hemispherical or global coordination geometries.10 was synthesized by the reaction of HeL5 and Cd2+.10 exhibits(3,4)-connected GoS topology and is the first bilayer MOFs pillared by monatomic Clr linker.(2)Post-synthesis modifications of MOFs,[Pt]+cations were loaded into the channels of compounds 6,7 and 9 to form stable composites,0.22[Pt]+@6,0.21[Pt]+@7 and 0.32[Pt]+@9 through electrostatic interaction.The composites remain the original frameworks and emit green light which is acute to naked eyes under UV light.In contrast,their mother frameworks emit blue light.(3)Detecting of NACs:A series of NACs can quench the photoluminescence of 1-9 and their composites either in suspensions or in vapors.In suspensions the quenching constants of the NACs toward quenching MOFs’ emissions follow the sequence of(?),indicating the MOFs bear higher sensitivities toward detecting dinoseb than other NACs.Thus the MOFs represent the first series of MOFs to function as promising photoluminescent probes for detecting dinoseb.In contrast,only NB vapor can quench the photoluminescence of 1-9 and their composites.(4)The assembly rules of the MOFs based on the low symmetric penta-and hexa-carboxylate ligands,and the detecting behaviors of the MOFs toward NACs are summarized.Stategies involving truncation and rearrangement of the carboxylate groups of the ligands,in situ self-adjusting of the carboxylate groups and decrease of connectivity number during the MOF assembly process play key role in the assembly of the MOFs based on the low symmetric ligands.The channel sizes of the frameworks,vapor pressures of the NACs,the electron transfer,long range energy transfer,and/or electrostatic interactions between the frameworks and NACs mainly contribute to the quenching process.