Synthesis, Structures And Properties Of Novel Metal-Organic Frameworks

Metal-organic frameworks (MOFs), a kind of functional molecular materials, have attracted much attention for their flexible tailoring, various topologies and promising application in ion-exchange, adsorption, molecular recognization, catalysts along with optics, electrics, magnetism and enantioselective separation. Metal-organic frameworks with rigid open frameworks, zeolite-like materials, possess not only porous phases similar to inorganic zeolites but also better performance in gas sorption and store than traditional zeolites. At the same time, MOFs can be endowed with multifunctional properties by selecting functional metal ions and organic ligands with functional groups.According to the principle of molecular engineering, we have focused our study on the synthesis, structures and multifunctional properties of MOFs with charming topologies. In this dissertation, we have prepared 15 new MOFs by using different organic ligands, and analyzed their topology structures as well as explored their multifunctional properties. These results will be introduced from the following four issues:(1) Realization of permanent porosity is the pre-requisite of porous MOFs for their application in gas storage, separation and heterogeneous catalysis. It is generally believed that rigid metal-containing secondary building blocks such as binuclear paddle-wheel M2(COO)4 (M = Cu2+ and Zn2+) and tetranuclear Zn4O(COO)4, and rigid organic linkers such as BDC, BTC and BPTC favor the construction of robust MOFs with high porosity. As Nature does not like "vacuum", most structurally porous MOFs collapse to form nonporous MOFs once the guest solvent molecules are removed under vacuum. In order to construct permanent pores, the frameworks need to be stabilized which can be fulfilled by framework interpenetration through some collaborative weakπ…πand C-H…phenyl interactions. To address this issue, we selected 4-Carboxycinnamic (CNC) and 3,6-Di-4-pyridyl-1,2,4,5-tetrazine (DPT) to synthesis a rare example of robustα-P0 type cubic MOF Zn2(CNC)2(DPT)·(DMF)1.5(H2O) (1) enforced by triple framework interpenetration. 1 is highly robust enforced by triple framework interpenetration through weak van der Waals interactions, thus the activated 1a can still keep the crystal structure and the activated 1b exhibits high hydrogen storage density of 95.2% at 1 atm and 77 K and a moderate high H2 adsorption enthalpy of 7.85 kJ/mol.(2) An important aspect of this relatively new chemistry is the analysis and direction of network topologies of the metal-organic frameworks, which is a precondition to make the true and significant development. So we designed a tetra-carboxylate ligand, 3,3',5,5'-azobenzenetetracarboxylic acid (H4ABTC), which can be acted as a well rigid rectangular-planar 4-connected ligand. We synthesised three compounds Cu2(ABTC)(H2O)2?(DMF)2(H2O) (2), Cd2(ABTC)(DMF)3?(DMF)2 (3) and Mn(H2ABTC)(DMF)2 (4), possessing NbO and PtS net topologies, respectively, from the Cu2+, Cd2+ or Mn2+ ions with the H4ABTC ligand. Of further interest, high-pressure hydrogen sorption of the activated 2a reveals a type I profile at 77 K which is saturated at 40 bar with a hydrogen uptake of about 4.71 wt%.(3) Compared with conventional porous materials, such as zeolites or activated carbons, MOFs have a greater potential because of tunable framework based on metal ions with various coordination geometries and multifunctional bridging organic ligands. We have successfully synthesized and characterized a series of novel 3D porous metal-organic frameworks Cd3(CTC)2(TED)(H2O)2?(H3O)2Cl2 (5) Cd3(CTC)2(Bipy)(DMF)2?(DMF)(H2O)2 (6), Cd3(CTC)2(Bpe)(DMF)2?(DMF)(H2O)2 (7), Zn3(CTC)2(Bipy)?(DMF)(H2O)2 (8), and Zn3(CTC)2(Bpe)?(DMF)(H2O)2 (9) in which metallic trinuclear secondary building units [M3(CO2)6N2] (M2+=Cd2+ or Zn2+) are connected by flexible CTC ligands and length-controllable diamine pillars. The metal-CTC-diamine synthetic strategy allows a systematical variation of the metal or the pillar to construct a series of open frameworks without changing the topology. Meanwhile, the water sorption and luminescent properties have been investigated at room temperature.(4) In order to rich the database of MOFs having mixed nodes topologies, we selected pyridine-3,4-dicarboxylate acid (3,4-H2PDC), which is an excellent unsymmetrical building block with multi-connecting ability, and transition metal ions (Cd2+, Zn2+ or Mn2+) to construct corrugated layers pillared by hmt or Bipy ligands, to generate six new 3D MOFs Cd2(3,4-PDC)2(μ2-hmt)(H2O)2?(DMF)2(H2O)2 (10), Zn4(3,4-PDC)4(μ2-hmt)(H2O)6?(DMA)4(H2O)5 (11), Cd2(3,4-PDC)2(Bipy)2(H2O)2?(DMA)3(H2O)4 (12), Cd2(3,4-PDC)2(Bipy)(DMF)(H2O)?(H2O)2 (13), Mn2(3,4-PDC)2(μ2-hmt)(H2O)2 (14) and Zn8(3,4-PDC)8(Bipy)3(DMA)2?(DMA)8(H2O)8 (15), which have various size and shape of channels. Remarkably, from the topological point of view, 10-13 exhibit three undocumented types of (3,4)-connected network, respectively, 14 exhibits rare (4,5)-connected network and 15 possesses an unprecedented (3,4,5)-connected network. In addition, methanol adsorption isotherms of the activated 10 and 13 reveal type I behavior with approximately 87.7 mg/g and 124.8 mg/g at room temperature, respectively.