Synthesis And Properties Of Organic Functional Group Modified Porous Metal Organic Frameworks

Recently, metal organic frameworks （MOFs） as new solid porous materials, have attracted tremendous attention for their potential applications in catalysis, sensing, gas and hydrocarbon adsorption and separation. It has been reported that the introducing organic groups with specific functionality into MOFs will not only manipulate and improve the pore properties of the modified structures, but also bring some new physical and chemical properties to the new compounds, while the parent structure topology is maintained. In order to understand the effect of the organic functional groups on the metal organic frameworks’performance, we have designed and synthesized a series of metal organic frameworks with different organic functional groups. The detail work as summarized below:The first part concerns the design and synthesis of two metal organic frameworks with methyl group Zn（BDC）（2,2’-DMBPY）_0.5·（DMF）_0.5（H₂O）_0.5 （1） and Zn（NDC）（2,2’-DMBPY）_0.5·（DMF）₂ （2）. Their structures were characterized by the single crystal X-ray diffraction, and the results showed that both compounds were three dimensional porous structures. In order to investigating the effect of methyl group on the properties of metal organic frameworks, we also synthesized their parent compounds Zn（BDC）（BPY）_0.5·（DMF）_0.5（H₂O）_0.5 （3） and Zn（NDC）（BPY）_0.5·（DMF）_1.575 （4）. The TGA and PXRD analysis indicates that the methyl group can enhanced the moisture stability of these compounds. The CO₂ adsorption study of the compound 1 and 2 compared with their parent compounds indicates that the isosteric heats of CO₂ adsorption is enhanced ,while the surface area and pore volume are reduced in both compounds as a result of introducing the methyl group to the BPY ligand. There are two contrary and competitive factors that control the CO₂ uptake capacity: the enhancement due to increased MOF-CO₂ interaction and the decrease due to the surface areas and pore volume reduction. For 1’ （the guest guest-free form of 1）, the positive effect dominates, which leads to a significantly higher uptake of CO₂ compared to its parent structure 3’ （guest free 3）, in 2’ （guest-free 2）, the negative effect rules, resulting in a reduced CO₂ uptake amount with respect to 4’. IR and Raman spectroscopic also provide indirect evidence of the interaction between CO₂ and methyl group. Furthermore, all four compounds exhibit high separation capability for CO₂ over other small gases.The second part deals with the design and synthesis of two novel 3D metal organic frameworks Zn₃（BPDC）₃（3,3’-DMBPY）·4DMF·H₂O （5） and Zn₃（BPDC）₃（2,2’-DMBPY）·X·solvent （6） , which were modified with the methyl groups. Their crystal structures were characterized by both single and powder X-ray diffraction methods, and their thermal stability were evaluated by TG analysis. The results indicate both compounds are thermally stable and recyclable. Compound 5 or 6 can be reversibly transformed to 1D compound Zn（BPDC）（H₂O）₂·H₂O by the exchange of the water molecule and bipyridine ligand. The gas adsorption of these compounds compared with parent compound 7’（guest free Zn₃（BPDC）₃（BPY）·4DMF·H₂O 7） was also investigated, and the results showed that the methyl group could enhance the isosteric heats of the CO₂ adsorption and reduce the surface area and pore volume of both compounds. The study is in agreement with the first part study.The third part of the thesis discusses the synthesis and characterization of two metal organic frameworks with nitro group Zn₂（BPDC-2NO₂）₂（BPY）·2DMF·H₂O （8） and Cu₂（BPDC-2NO₂）₂（BPY）·X·solvent （9）. Their structures were characterized by the single crystal X-ray diffraction and PXRD, and the thermal stability and water stability of these compounds were investigated by the TGA and PXRD. The results show that the water stability property can be enhanced by the nitro group.In the fourth part, three dicarboxylate ligands with the amino group BPDC-2NH₂, 4,4’-（4-（4-aminophenyl）pyridine-2,6-diyl）dibenzoic acid and 3,5-bis（4-carboxylic acid phenyl）aniline are the main subject. All of these ligands were characterized by the MP, ¹H-NMR and ¹³C-NMR. We have attempted to synthesize new MOFs using these ligands, and the results are summarized.