Syntheses,Structures And Properties Of Coordination Polymers Based On The Nitrogen Heterocyclic Carboxylate Ligands

Coordination polymers?CPs?have become a new functional material with great functional application value in the fields of optics,magnetism,electrochemistry,biology,catalytic chemistry and so on because of their versatile structures and excellent properties.Therefore,in recent decades,the reasonable construction of functional CPs has been received intense attention from researchers.The preparation of CPs is affected by many factors,such as the molar ratio of metal ions to organic ligands,reaction temperature,reaction time,solvent conditions,pH value of the system,counter ions and so on.Through the reasonable regulation of these factors,the compounds with diverse structures and excellent properties can be obtained,and the selection of organic ligands is very important.Carboxylate and nitrogen-containing ligands are the most commonly used ligands in the synthesis of coordination polymers,in which carboxyl groups tend to promote the diversification of the structure of compounds by forming metal-carboxyl structural units with metal ions.The nitrogen-containing groups have more advantages than carboxyl groups in forming strong coordination bonds with transition metal ions to improve the stability of the compounds.Therefore,combining the advantages of these two groups and introducing them into the same reaction system,it is beneficial to obtain new functional compounds which takes into account the structural stability and novelty.The dissertation is aimed at constructing compounds with excellent optical and magnetic properties.Twenty-six compounds are successfully designed and synthesized under hydro/solvothermal conditions by the reactions of three nitrogen heterocyclic carboxylate ligands with different metal ions.The structures of compounds were characterized by X-ray powder diffractometer,and they were characterized by elemental analyzer,infrared spectrometer,X-ray single crystal diffractometer.In addition,the thermal stability of these compounds was measured by thermal analyzer.At the same time,the luminescent and magnetic properties of some compounds were studied.The dissertation includes five chapters as follows:Chapter 1:The concept and synthesis methods of CPs were summarized.The optical and magnetic applications and research status of coordination polymers were introduced.Reviews onresearchdevelopmentofcompoundscontainingtriazolecarboxylateand pyridine-carboxylate were briefly summarized.Chapter 2:Seven compounds with different structures?1-7?were constructed by the reaction of semi-rigid ligands 1-?4-benzoic acid?-3-?pyrazinyl?-1H-1,2,4-triazole?HL1?containing pyrazinyl,triazole and carboxyl groups with metal ions?Zn?II?,Cd?II?,Co?II?,Mn?II?and Pb?II??under the condition of selective introduction of different auxiliary ligands.The discussion on the structures of 1-7 shows that the reaction conditions such as temperature,solvent ratio and pH value can influence the construction of novel and different complexes.The luminescent properties of compounds 1-4 and the magnetic properties of compounds 5and 6 have been studied,it is found that compounds 1-4 have good fluorescence properties.Compound 3 shows high selectivity and sensitivity for fluorescence detection and recognition of Fe³⁺in aqueous solution.Compounds 5 and 6 exhibit antiferromagnetic behavior.At the same time,compounds 1-7 have excellent thermal stability.Chapter 3:Three new series of lanthanide?Eu?III?,Tb?III?,Sm?III?,Gd?III?,Dy?III?,Ho?III?,Nd?III?,Yb?III?,Er?III??coordination polymers?8-18?assembled through HL1 were solvothermally constructed.It is found that the counter ions and solvent ratio play an important role in the construction of 8-18 through structural comparison.The solid-state luminescence properties of complounds 8-18 were tested.The results show that 8-Eu and9-Tb exhibit characteristic red light and green light and blue light emission based on ligand,respectively.So,HL1 can sensitize the luminescence of Eu?III?and Tb?III?ions to a certain extent.Therefore,a series of Eu?III?-doped Tb?III?compound with different proportions were prepared by chemical doping method,and their solid-state fluorescence properties were determined in order to obtain white light emission.And the Eu?III?/Tb?III?molar ratio and the excitation wavelengh?[Eu?III?/Tb?III?]=2/3,340 nm?were determined to gain the nearly white light emission.In addition,the compound 9-Tb has been applied in the high selectivity and sensitivity detection of Fe³⁺in aqueous solution.The magnetic properties of compounds11-Gd,12-Dy,13-Ho,15-Yb and 16-Er were determined,and it was found that compounds 11,13,15 and 16 showed antiferromagnetic behavior.On the other hand,12 showed ferromagnetic behavior in the low temperature range?5.0 K-2.0 K?.Chapter 4:Three compounds?19-21?with different dimensions were synthesized by solvothermal reaction of 5-?3,4-dicarboxyphenoxy?nicotinic acid?H₃L2?with metal ions?Cd?II?,Cu?II?and Pb?II??.The determination of fluorescence properties of 19 and 21shows that compound 19 has excellent luminescent properties and nanosecond fluorescence lifetime,and 19 shows excellent selectivity and sensitive detection and recognition ability to nitrobenzene.In addition,the compounds?19-21?show excellent thermal stability.Chapter 5:Fivecompounds?22-26?weresynthesizedbythereactionof5-?2,3-dicarboxyphenoxy?nicotinic acid?H₃L3?with transition metal ions(Zn?II?,Co?II?,Cu?II?,Cd?II?and Mn?II?at 120°C and 105°C,respectively.The fluorescence properties of compounds 22 and 25 show that both of them have excellent fluorescence properties,in which compound 22 can be used as a sensitive and reproducible fluorescence probe for the detection of Cu²⁺.The magnetic properties of compounds 23,24 and 26 show that they all have antiferromagnetic behavior.At the same time,the compounds 22-26 showed good thermal stability.