The Study On Construction And Properties Of Metal Organic Framework Multifunctional Materials Based On Multi-nuclear Metal Clusters And Isonicotinic Acid

In the mid-1990s,porous metal-organic framework（MOF）materials were first discovered and have been rapidly developed by many researchers over the past two decades.Metal ions and organic ligands self-assemble by coordinate covalent bonds to form MOF.Due to the high surface area,tunable pore structure and flexible functionalization,MOF has become a multifunctional material with potential in the fields of optics,electricity,magnetism,sensing,catalysis,and biomedicine.Choosing the metal clusters with interesting configuration as second building units（SBUs）can not only bring more properties to the MOF material,but also prevent interpenetration of the framework for large pore volume and higher thermal stability.Therefore,high-nuclear cluster-based MOF has become a hot research in this field.In order to study the synthesis,structures and related properties of cluster-based MOF,isonicotinic acid（Hin）was selected as an organic ligand in this dissertation.Under the solvothermal conditions,a series of MOFs based on the SBUs with novel architectures（triangular,dimeric triangle,1D chain based on triangle,cubane,square-planar,and macrocyclic）and properties were synthesized.The coordination habits of ligands and the influence factors of structures were studied in detail.And then we studied the magnetic properties,gas adsorption and separation,and electrochemical properties of MOF-derived materials.The results show that Hin,as a typical semi-rigid multidentate ligand,tends to"capture"multiple metal ions to form cluster-based porous MOFs under a solvothermal reaction.The main contents of our work are summarized below:（1）Two neutral/cationic MOFs,[Mn₃（μ₃-OH）（in）₄（CH₃COO）（H₂O）]·H₂O（1）and[Co₃（μ₃-OH）（in）₄（DMA）₂（H₂O）]ClO₄·DMA·3H₂O（2）,based on triangular SBUs with the same hex topology are successfully constructed by using charge control approach of the SBUs,whose charges of frameworks are controlled by synergistic effect of counterion,solvent and metal center.The desolvated framework of 2 displays Langmuir surface area of839 m² g^-1 and more effective sorption capacities of N₂,CO₂ and H₂ than 1,which is probably due to the cationic 2 has larger effective aperture and stability than neutral 1.Magnetic studies show dominant antiferromagnetic behaviours for both 1 and 2.Therefore,using SBU charge controlling concept could be an effective strategy for construction of porous neutral and ionic frameworks.（2）Based on the research on the triangular SBU,we present the first two examples of3D Hin-based MOFs with planar Co₆ clusters and Mn₆-based alternating 1D chain as SBUs.（CH₃）₂NH₂[Co₆^II（μ₃-OH）₂（in）₆（HCOO）₃（NO₃）₂]·4DMF（3）and[Mn₆^II（μ₃-OH）₂（in）₆（CH₃COO）₄]·2H₂O（4）.Both compounds 3 and 4 contain a triangular M₃^II（OH）central unit,which is connected by rare syn,anti,syn,anti-and syn,syn,anti-coordinated formates or acetic acid anion coligands to the other neighbouring triangular units forming hexnuclear cluster or 1D infinite chain as new SBUs.These SBUs connected to 9 or 10 Hin linkers,respectively,to form two different frameworks.Compound 4 exhibits an extraordinarily high moisture-stability.Both compounds 3 and 4 have good thermal stability.Magnetic studies indicate that compound 3 exhibits antiferromagnetic behavior,and compound 4shows spin-canting antiferromagnetic behavior.（3）Two new 3D cobalt MOFs,[Co₄（CH₃COO）（in）₅（μ₃-OH）₂]·2H₂O（5）and[Co₄（SO₄）₂（in）₄（DMF）₂]·3DMF（6）,have been prepared through anion template method.Compound 5 consists of rare odd-number connected（9-connected）cubane-like SBUs,while compound 6 consists of 8-connected high-symmetry square-planar cluster as SBUs.Magnetic studies indicate that compound 5 exhibits spin-canting antiferromagnetic ordering,while compound 6 shows antiferromagnetic behavior.At 273 K under 1 bar,compound 5exhibits a high CO₂ selectivity over CH₄ and a significant CO₂ uptake of 13.6 wt%,which is higher more than 6（8.5 wt%）.Furthermore,compound 5 was then transformed into ultrasmall Co₃O₄ nanoparticles via simple but effective annealling treatment.Electrochemical measurements show that the Co₃O₄ nanospheres derived from compound 5exhibited high and stable lithium storage properties(1100 mA h g^-1 after 100 cycles at 200mA g^-1)and excellent rate capabilities.These results give good examples to explore the role of classical geometry SBUs in the assembly of cluster-based MOFs,which provide an effective strategy for constructing multifunctional materials,including multimagnetic porous materials and anode materials for electrochemical applications.（4）A stable hex-type MOF,[Mn₃（OH）（CH₃COO）₂（in）₃]·H₂O（7）,was constructed by nano-sized[Mn₁₈^II]metallamacrocycle SBU,being the one with the highest nuclearity of pure bivalent manganese wheel-like node based on[Mn3]triangles in the microporous MOF.7 exhibits good thermal and moisture stabilities.7 also shows effective H2,CO2 adsorption with an effective CO₂/CH₄ selectivity.We calculated the H₂ binding nature for 7 by PM6-D3 calculations.It is indicated that the H₂ molecule is strongly adsorbed between two neighboring carboxylate O atoms in 7 with strong hydrogen bonding interactions.Magnetic studies show that there exists antiferromagnetic behaviour in 7.Among all the reported high-nuclear manganese MOFs,7 is the first 3D carboxylic acid-based pure divalent manganese（{Mn_x}x≥12）compound that magnetic property has been investigated.The incorporation of porosity and magnetism in 7 provides a significant candidate of multifunctional molecular materials.Importantly,the successful synthesis of 7 confirms the feasibility of synthesizing novel high nuclear SBU through a judicious choice of appropriate ligands and metal salts to construct microporous MOF.