Synthesis, Characterization And Properties Of Tetrazolate-Based Metal-Organic Framework Materials

The architectures of Metal-Organic Frameworks (MOFs) are mainly dependent on the assembly of metals and organic ligands. Metal-organic framework materials have been paid much attention in recent years due to their potential applications in gas storage, separation, sensing and catalysis. The organic ligands play an important role in the self-assembly process of MOFs. Because the tetrazole group possesses four nitrogen atoms and different coordination modes, the ligand with tetrazole group is easy to form polynuclear metal clusters or chain building blocks. In this thesis, eight porous MOFs were synthesized by selecting H2bdt (1,4-benzeneditetrazol-5-yl) ligand which consists of double tetrazlole groups and benzene ring under hydrothermal or solvothermal conditions. The detailed structural features and physical properties (such PXRD, TGA and fluorescence) of these MOFs have been investigated. The research purpose and main content of this work have also been outlined.Compound [H2N(CH3)2][Cd4Cl(H2O)4(bdt)4]·5H2O·3DMF (1) was solvothermally synthesized by employing Cd(NO3)2-4H2O and H2bdt ligands in mixed N,N’-dimethylformamide (DMF) and1,3-Dimethyl-2-imidazolidinone (DMI) solvents. X-ray diffraction analysis of1revealed a tetragonal metal-organic framework structure, and the structure may be described in terms of the secondary building units{Cd4Cl} linked through the phenyl tether of the bdt ligand into a framework structure. To the best of our knowledge, compound1is the first sample of8-connected bcu net constructed by {M4Cl} squares and a linear tetrazoles ligand.When the KC1was added to the synthesis system of1, a new3D framework K[Cd(bdt)Cl]-2DMI (2) was obtained. X-ray crystallography reveals that compound2has a3D anionic porous framework constructed from1D Cd-tetrazole-Cl chains [Cd3(tz)6Cl3]n, which is charge-balanced by K+cations. Futhermore, it also features a cubic structure with classical8-connected bcu topology.Both compound [Cd2(H0.67bdt)3]·2H2O (3) and [Cd(bdt)(H2O)2]-4H2O (4) were hydrothermally synthesized. Compound3is a three-dimensional metal-organic framework material which is construted by Cd-tetrazole rod secondary building units (SBUs) via covalent links. While compound4is a3D framework construced by {Cd(tz)4(H2O)2}n two-dimensional layers via covalent links.Presented here are two novel three-dimensional metal-organic frameworks [H2N(CH3)2]2[Cd5(bdt)3(btc)2(H2O)2]-3H2O (5)(H3btc=1,3,5-benzenetricarboxylic acid) and [Cd5(Hbdt)2(bdt)(btc)2(H2O)2]-4H2O (6) with integrated topological nets, where the trinuclear cadmium units act as10-connected nodes. Since both compounds are built from a dual-ligand assembly approach, the topological analysis on the networks of compounds5and6are also considered as the integration of two nets. For compound5, its (3,4,4,4,10)-net is integrating a xbe net of Cd-bdt connectivity and kgd nets of Cd-btc connectivity, while the (3,4,4,4,4,4,10)-net of compound6is integrating a fry net of Cd-bdt connectivity and kgd nets of Cd-btc connectivity.Very lucky, we obtained two compounds [Zn2(bdt)(Hbtc)]-H2O (7) and {Zn2[BH(im)3]2(bdt)}-2DMI (8) by choosing Zn(NO3)2and the auxiliary ligands. Compound7is a3D tfz-d net which is integrating a kgd net of Zn-bdt connectivity and1D chains of Cd-btc connectivity. In compound8, a layered architecture is formed from the connectivity between [BH(im)3]-ligands and [Zn(tz)]+units. The given2D layer linked to two adjacent layers by sharing phenyl groups of the bdt ligands to form a3D neutral porous framework.The experimental results described here show that we obtained a number of interesting metal-organic framework materials base on H2bdt ligand under hydrothermal and solvothermal conditions. All of the compounds were characterized by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and fluorescence analysis. And we hope this accumulation of experimental data can provide some examples on topology analysis and further demonstrate the relationship between the product and synthesis method.