Construction,Luminescence Sensing And Magnetic Properties Of Coordination Polymers With Azacyclic Ligands

The design and synthesis of coordination polymers with unique properties and novel structures has attracted considerable attention at home and abroad,not only because of their structural diversity and designability,but also because of their potential applications in gas adsorption/separation,magnetism,luminescence and catalysis,etc.However,the structures of compounds may be affected by many factors,so it is still a challenge to construct compounds with specific structures and properties.In order to further explore the relationship between structures and properties,thirty-two novel compounds based on four kinds of azacyclic organic ligands and metal salts are synthesized by self-assembly method under hydrothermal/solvothermal conditions.According to the different structures,the magnetic properties,the applications of luminescence recognition and detection,and the adsorption and separation properties of dyes are studied.The work covers the following three parts.1.Magnetic and luminescence sensing properties of compounds with methyl functionalized pyridyl-phthalic acidPyridyl-phthalic acid is a kind of bifunctional ligands that i ncorporate both the pyridyl group and the carboxylate groups.In recent years,coordination polymers based on such bifunctional ligands have been studied widely in the field of coordination chemistry,photochemistry and magnetochemistry.The advantages of these ligands as follows:（i）They have special luminescence properties which are favorable to synthesis materials with optical properties;（ii）The conjugate system is beneficial to the effective transfer of electrons;（iii）The pyridyl nitrogen（N）atoms have special properties which can selectively recognize and adsorb some small molecules or heavy metal ions;（iiii）the carboxylate groups as the short bridges can bind two or more metal ions and they can efficiently mediate magnetic coupling.Therefore,we have designed and synthesized some compounds based on the pyridyl-phthalic acid ligand.These compounds are expected to exhibit novel structures and rich properties.（1）Fourcompoundsaresynthesizedbythereactionof4-（3,5-dicarboxylphenyl）-2-methylpyridine（H₂L¹）,and Zn（Ⅱ）,Mn（Ⅱ）,Co（Ⅱ）and Ni（Ⅱ）ions under solvothermal conditions.The crystal structures and topologies of these compounds are studied and analyzed in detail.The effects of counter ions on the structure and properties of the compounds are also discussed.Zn（Ⅱ）compound shows strong blue luminescence.Mn（Ⅱ）compound exhibits antiferromagnetic behaviors while Co（Ⅱ）and Ni（Ⅱ）compounds transfer ferromagnetic couplings.（2）Eight isomorphic compounds are constructed by the reaction of H₂L¹ and rare earth ions.These compounds are the（4,4）lattice-like 2D frameworks in which dinuclear units with double carboxylate bridges are interlinked by single carboxylate bridges from organic spacers.Magnetic investigations indicate that the carboxylate bridges transmit intralayer antiferromagnetic coupling in Nd（ⅡI）,Gd（ⅡI）and Ho（ⅡI）compounds but transmit intralayer ferromagnetic coupling in Dy（ⅡI）compound.Furthermore,Dy（ⅡI）compound also displays slow magnetic relaxation behavior with a high relaxation energy barrier.The luminescence investigations show that Eu（ⅡI）and Tb（ⅡI）compounds can serve as highly selective and recyclable sensing materials for nitrobenzene,Fe³⁺ions and Cr₂O₇^2-ions.The mechanism of luminescence recognition is also discussed.This work establishes a solid foundation for luminescence compounds in the field of theoretical research and practical application.2.Magnetic and luminescence sensing properties of compounds with carboxyl functionalized pyridyl-phthalic acidCarboxyl functionalized pyridyl-phthalic acid is also a kind of ligands with bifunctional groups.They possess the advantages of magnetic and luminescence properties of methyl pyridyl-phthalic acid ligands,and they have more diverse coordination modes.Therefore,we use these ligands to construct novel compounds with unique magnetic and luminescence properties.（1）FourMn（Ⅱ）,Co（Ⅱ）,Ni（Ⅱ）andCo_1.01Ni_1.99compoundswith4-（3,5-dicarboxylphenyl）picolinic acid（H₃L²）have been obtained.The metal ions are linked by the single carboxylate bridge to give linear trinuclear units.The trinuclear units are connected through the other single carboxylate bridge to give a 2D（4,4）layer,and the layers are interlinked by the organic ligands into 3D structures.Magnetism studies indicate that antiferromagnetic coupling between metal ions are mediated by the single carboxylate bridges in the Mn（Ⅱ）and Co（Ⅱ）compounds while ferromagnetic coupling are observed in the Ni（Ⅱ）compound.It is noteworthy that the compound doped with Co（Ⅱ）and Ni（Ⅱ）exhibits complicated magnetic competition behavior.This phenomenon is of great academic significance for exploring the relationship between magnetic properties and structures.（2）Seven novel 2D or 3D compounds are synthesized by the reaction of3-（3,5-dicarboxylphenyl）-4-carboxylpyridine（H₃L³）and a system of pyridine ligands4,4’-bipyridine（4,4’-bpy）,2,2’-bipyridine（2,2’-bpy）and phenanthroline（phen）as auxiliary ligands.As 2,2’-bpy and phen as coligands,2D structures was obtained,and the others show 3D structures.Magnetic studies show that Co（Ⅱ）compounds transmit antiferromagnetic couplings.Cd（Ⅱ）compounds display strong luminescence emission.Furthermore,Cd（Ⅱ）compound with 4,4’-bpy auxiliary ligand exhibits a microporous anionic framework with accessible Lewis-base sites（N）,which makes the compound a good candidates as luminescence sensing and ion exchange material.The results show that the compound can selectively recognize Fe³⁺ions and nitro explosives（TNP）.More interestingly,this compound can adsorb cationic dyes in aqueous solution.（3）We also have obtained four mononuclear isomorphic 3D compounds by the reaction of H₃L³ and Nd（ⅡI）,Eu（ⅡI）,Dy（ⅡI）,Ho（ⅡI）ions.Nd（ⅡI）,Dy（ⅡI）and Ho（ⅡI）compounds all exhibit antiferromagnetic behaviors,and Dy（ⅡI）compound exhibits slow relaxation behaviors at low temperature.Eu（ⅡI）compound can efficiently selectively detect Fe³⁺ions,Cr₂O₇^2-ions and amine organic molecules in aqueous systems.3.Syntheses and properties of azide compounds with in situ synthesis of pymCN with azide ions.Azide and tetrazolate groups have the various coordination modes that can effectively mediate magnetic couplings.Therefore,we expect to construct novel molecular magnetic materials by using the azide-tetrazolate mixed bridges.In order to effectively synthesize mixed bridging compounds and discuss the law between magnetic properties and structures,five novel isomorphic Co_2-xZn_x（0<x<2）compounds are synthesized by the in situ reaction of pymCN,azide ions and metal salts under hydrothermal conditions.They exhibit 3D frameworks in which 1D coordination chains with mixed double azide and tetrazolate bridges are linked by the organic ligands.The homometallic Co^Ⅱ compound exhibits the coexistence of antiferromagnetic ordering and slow magnetic dynamics.The bimetallic Co^Ⅱ_2-xZn_x^ⅡI series mainly show ferromagnetic interaction but the slow relaxation behaviors of the compounds are compressed as the composition of Zn increasing.We also study the luminescence properties of these compounds.Single metal Zn complexes have strong fluorescence emission,and the luminescence of Zn complexes decreases gradually with the increase of Co ions.The homometallic Zn^Ⅱ compound exhibits strong luminescence while the luminescence intensity of bimetallic Co^Ⅱ_2-xZn_x^Ⅱ gradually decreases as Zn^Ⅱ ions are replaced by Co^Ⅱ ions.