Study On Assemblies,Structures,Sensing And Magnetic Properties Of Novel Coordination Polymers And Their Composites

The sensors based on coordination polymers（CPs）have gained wide research attentions because which possess the advantages of good selectivity,high sensitivity,simple operation and low cost.At present,such sensors are mainly used in the fields of fluorescence sensing and electrochemical sensing.In addition,the study of polynuclear cluster CPs based on transition metals is of great significance for exploring advanced magnetic materials and understanding the relationship between molecular structure and magnetic behavior.In the process of CPs synthesis,the geometry,functional group,symmetry,size and coordination pattern of a ligand can greatly affect the final structures of CPs.Compared with organic linkers,metal ions play particularly prominent roles in regulating the self-assembly process,because different valences determine the coordination number and coordination tendency.In many ligands,polycarboxylic acid ligands with strong coordination abilities and varied coordination modes are considered to be a good choice,and which is easy to produce polynuclear clusters and high-dimensional framework.In order to enhance the functions of CPs,functional groups such as imidazolyl group,hydroxyl group,ether oxygen group and amide group are usually modified on carboxylic acid ligands.The synthesis methods of CPs are abundant and varied,except for the most widely used solvothermal direct synthesis,guest molecules or ions can be introduced into the porous CPs,namely metal-organic frameworks（MOFs）through in situ composition,ion doping,coordinated postsynthetic modification and other postsynthetic strategies.These methods could enhance the properties of original materials or expand new functions without affecting the integrity of the whole framework of MOFs.Based on the above discussion,two polycarboxylic acid ligands N,N′-bis（4-phthalic acid）（H₄bpa）and5,5′-oxidiisophthalic acid（H₄odip）were selected.Under solvothermal reaction,several CPs with novel structures and good stabilities were obtained.Furthermore,two MOFs with large pores were selected for post modification synthesis.The fluorescent and electrochemical sensing,as well as magnetic property were further studied.This dissertation is divided into five chapters:Chapter 1:The concept,synthesis method and application of CPs in the fields of fluorescence sensing,electrochemical sensing and magnetic materials were introduced.Chapter 2:In order to explore the metal ions-controlled syntheses of CPs,the temperatures and solvent ratios were fixed in the reaction processes.Five CPs[Zn（bpa）_0.5（H₂O）₂]_n（1）,[Co（bpa）_0.5（H₂O）₂]_n（2）,[Mn（H₂bpa）（H₂O）₂]_n（3）,[Ca（H₂bpa）（H₂O）₂]_n（4）and[Ba（H₂bpa）（H₂O）₂]_n（5）were synthesized with H₄bpa ligand.H₄bpa shows very versatile coordination modes and leads to various frameworks,including isomorphous 2D grid-like layer based on M₂O₂ cores for 1 and 2,isomorphous4-connected 3D PtS frameworks based on 1D[M（CO₂）₂]_n chains for 3 and 4,and a 2D wave-like layer based on[BaO₃]_n chains for 5.Moreover,2 and 3 reveal the antiferromagnetic and ferromagnetic properties,respectively,while 1,4 and 5 possess strong solid state luminescence.Chapter 3:By employing H₄ odip ligand,new alkaline earth-metal organic frameworks（AE-MOFs）,i.e.{[Mg₂（μ₆-odip）（μ₂-OH₂）（H₂O）₄]·DMF}_n（3）,[Ca₂(μ₁₀-odip)（Et OH）]_n（4）,[Sr（μ₆-H₂odip）（MeOH）]_n（5）and{[Ba_1.5（μ₅-H₂odip）（μ₄-H₃odip）（H₂O）₃]·2（H₂O）}_n（6）were synthesized under solvothermal reaction.H₄odip shows versatile coordination modes as well as various topologies in these MOFs.6 forms a uninodal 4-connected（6⁶）-dia 3D topology based on dinuclear Mg₂（COO）₂（μ₂-OH₂）clusters.7 displays an unprecedented3-nodal（5,5,10）-connected 3D net based on 1D[Ca（COO）]_n chains and dinuclear Ca₂（COO）₂ clusters.8 indicates a uninodal 6-connected 3D net with(4¹⁰·6⁵)-sma topology based on 1D[Sr（COO）]_n chains.9 features a new 4-nodal（4,5,6,6）-connected net based on two types of 1D chains.Four AE-MOFs show solid-state fluorescent properties at ambient temperature.Especially,6 and 7 have multiresponsive recognition of Fe³⁺and Pb²⁺ions,Fe³⁺and Cu²⁺ions,respectively,while 8 and 9 show single selective detection for Fe³⁺ion,signifying that they could be potential fluorescent sensors for specific heavy metal ions in water system.Chapter 4:Utilizing the oxygen-bridged H₄ odip ligand,one 3D porous MOF{[Ni₂（odip）（H₂O）₄（DMF）]·DMF·2H₂O}_n（10）with a rare 3-nodal（3,3,4）-connected topological net based on two types of Ni₁₂（odip）₁₂ and Ni₂₄（odip）₁₂ nanocages was prepared.To exploit the advantage of high porosity,10 was employed as a MOF matrix,then photoactive Eu³⁺ions were introduced through a facile soaking method to get Eu³⁺functionalized MOF composite Eu³⁺@10.The composite was characterized and analyzed detailedly.Luminescent sensing experiment demonstrated Eu³⁺@10 has the potential to serve as a sensitive,recycle and fast luminescent probe for aspartic acid,with a quenching constant of 1.565×10³ M^-1.The result offers a new possibility to realize the similar luminescent sensing function as lanthanide MOFs for many MOF materials which are non-emissive and/or difficult to synthesize directly.Moreover,10 reveals a ferromagnetic character in the range of 7-50 K.Chapter 5:Utilizing the oxygen-bridged V-shaped H₄odip linker,MOF{[Co₅（odip）₂（OH）₂（OH₂）₂（H₂O）₄]·2DMF·H₂O}_n（11）with[Co₅（μ₃-OH）₂（μ₂-OH₂）₂]⁸⁺pentanuclear cluster was prepared.The glassy carbon electrode was modified by 11,and the obtained electrode revealed electrocatalytic performance for glucose oxidation.The porous MOF matrix is beneficial for dispersing Ag nanoparticles evenly in the interior cages or channels,so Ag@11 composite composed of both Ag nanoparticles and MOF was further prepared through deposition-reduction method to enhance electrocatalytic activity.The result demonstrates that the glucose oxidation by Ag@11 was greatly increased with low detection limit（1.32μM）,good selectivity and sensitivity(0.135μAμM^-1),which promotes the application of MOF-template porous composites as advanced electrochemical sensor materials.Furthermore,11 shows an interesting magnetic spin-glass slow dynamics for the existing of peculiar pentanuclear Co（Ⅱ） clusters.