Synthesis,Structure And Sensing Properties Of Coordination Polymers And Lanthanide Metal-Organic Frameworks

Starting from small molecules,three new pyridine carboxylic acid ligands H2L1,H2L2 and H2L4 were prepared by Aldol condensation and Kr?hnke pyridine synthesis.By adjusting the reaction conditions such as temperature,pressure,solvent type and proportion,a series of coordination polymers(CPs)and Ln-MOFs with unique structures were synthesized by the ligands and different metal salts in the high-pressure reactor.The structures and properties of CPs and Ln-MOFs were characterized by single crystal X-ray diffraction(SCD),powder XRD(PXRD),infrared spectrometer(IR),fluorescence spectrometer(PL),etc.Four coordination polymers[M(L1)(H2O)2]·3H2O,(M=Mn(1),Co(2),Cd(3)and Zn(4))were prepared by the reaction of H2L1 containing pyrazine rings with transition metals.Four coordination polymers with different isomers were prepared by H2L2 with furan rings and transition metals under the same conditions.Respectively[Mn(L2)(H2O)2](5)and[Ni(L2)(H2O)2]·H2O(6),7(Cd-CP)and 8(Zn-CP).All the eight CPs had one-dimensional chain structure.It was found that the different ligand substituents caused the structural differences of CPs 1-8.Ligand L12-adopts η3chelating fashion.L22-is a L-shaped building block.Compared with pyrazine N atom,furan O atom has weak coordination ability and does not necessarily participate in coordination.When substituents change from pyrazine to furan ring,the crystal structure also changes from one-dimensional zigzag chain to one-dimensional molecular box chain and one-dimensional linear chain.The results show that the substituent group can regulate the crystal structure.The ligand H2L4,which is developed based on H2L1 and H2L2,has a larger molecular size.Combined with lanthanide metals with characteristic luminescence,four isomeric three-dimensional lanthanide metal organic frameworks were prepared,namely,MOF-1(Eu),2(Tb),3(Gd)and 4(Y).The results show that MOF-1-4 has strong fluorescence emission,MOF-1 and MOF-2 show characteristic red light and green light,respectively.The carboxyl group on L42-in the crystal has three coordination modes,forming the rare trinucleated SBUs.In addition,MOF-1-4 showed rapid and sensitive recognition ability to Fe3+and Cr2O72-in aqueous solution,and the fluorescence was quenched by energy competitive absorption and weak interaction.In the presence of other cations or anions in aqueous solution,the sensor detection also shows excellent selectivity and anti-interference ability.Cyclic experiments show that MOF-1-4 can be reused in sensing detection.