Synthesis, Structure And Properties Of Porous And Chiral Metal-Organic Frameworks

Metal-organic frameworks (MOFs) as novel multifunctional materials, have attracted much more attentions because of their flexible tailoring, various topologies and promising application in hydrogen storage, ion-exchange, adsorption, molecular recognization, catalysts along with optics, electrics, magnetism and enantioselective separation. These open MOFs possess not only porous phase similar to inorganic zeolites but also better performance in gas sorption and storage than traditional zeolites. In addition, according to the principle of crystal engineering, it is possible that rational design and synthesis of porous crystalline materials by selecting certain geometric metal ions and special organic ligands. 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 28 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 seven issues:(1) One of our interests is to prepare MOFs with zeolite topologies by using 4-connected organic ligand or constructing inorganic and organic 4-connected building units. To address this issue, we have synthesized three novel MOFs, [Cd(H₂O)₃]34(hmt)17·Cl68·46(H₂O)·68(DMF) (1) with zeolite MTN topology, Cd(CTC)(H₂O)·(HPIP)0.5(H₂O) (2) with zeolite ABW topology and Cd(CTC)·(HIPA) (3) with zeolite BCT topology by utilizing hmt (hmt = hexamethylenetetramine) or H3CTC (CTC = cis,cis-1,3,5-cyclohexanetricarboxylate) ligand in the presence of different organic amine. In these MOFs, Polymer 1 successfully expands the original structure of zeolite MTN and is very limited as a zeolite-like material with a cation framework. Additionally, we also studied their thermal stability, ion exchange and adsorption properties.(2) We also focused our study on the effects of different organic amines, TEA (triethylamine), bpy (4,4'-bipyridine) and hmt in the synthesis of flexible saturated H3CTC ligand coordinated to metal ions. We synthesized four novel MOFs, Mn3(CTC)₂ (DMF)₂(4), Cd₃(CTC)₂(H₂O)₃·(H₂O)(5), Cd₃(CTC)₂(bpy)₂(EG)₂(6) and Cd₃(CTC)₂(hmt)(DMF)(C2H5OH)(H₂O)·2(H₂O)(7), and analysed their topology structures as well as examined their thermal stability and photoluminescence properties.(3) Further, we focused our research on the effects of different organic amines as templates in the synthesis of rigid H3BTC ligand (BTC = 1,3,5-benzenetricarboxylate) coordinated to metal ions. Such amines include diethylenetriamine (DETA), cyclohexylamine (CHA), triethylamine (TEA), tri-n-propylamine (TPA), and tri-n-butylamine (TBA). Seven novel MOFs, [Cd(HBTC)₂]·2(HDETA)·4(H₂O) (8), [Cd2(BTC)₂ (H₂O)₂]·2(HCHA)·2(EtOH)·2(H₂O) (9), [Cd5(BTC)₄Cl4]·4(HTEA)·2(H₃O) (10), [Cd₃(BTC)₃(H₂O)]·(HTEA)·2(H₃O) (11), [Zn(BTC)(H₂O)]·(HTPA)·(H₂O) (12), [Cd(BTC)]·(HTPA)·(H₂O) (13) and [Cd2(BTC)(HBTC)]·(HTBA)·(H₂O) (14) have been prepared in this chapter. We analyzed their topology structures and studied their thermal stability and ion exchange properties. At the same time, their nonbonding interaction energies (Einter), including H-bonding and van der Waals, have also been examined. We believe that the discovery of the templating effect of organic amine cations, together with the study of the calculated nonbonding interaction energies in these host-guest systems, would direct the synthesis of novel architectures and facilitate the exploration of new MOFs with charming molecular topologies and multifunctional properties.(4) Our strategy for preparing chiral MOFs is to introduce chiral solvent as well as build from achiral units by the spontaneous chiral resolution. In the appropriate condition, we successfully synthesized three chiral MOFs, Zn3(BTC)₂(DMF)3(H₂O)·(DMF)(H₂O) (15), Cd4(BTC)3(DMF)₂(H₂O)₂·6(H₂O) (16) and Cd2(bpdc)3·4(DMF)(bpdc = 4,4'-biphenyldicarboxylate) (17). We also analyzed their topology structures and studied their thermal stability, photoluminescence and adsorption properties. Interestingly, polymer 17 exhibits a homochiral metal-organic nanoporous framework with about 18.3 ?×22.4 ? hexangular nanotube-like channels constructed from eight intertwined left-handed helices. To the best of our knowledge, polymer 17 includes the maximum homochiral helices in MOFs. (5) At the same time, we focused our study on the synthesis of MOFs with mixed 3d-3d metal ions because such MOFs are very limited and the study of their multifunctional properties has not been reported so far. Our strategy for preparing such 3d-3d heterometallic MOFs is to partially replace the 3d metal centers of clustered SBUs by other 3d metal ions. To implement this issue, we synthesized a porous MOF with trinuclear znic-carboxylate SBUs, [Zn3O(BTC)₂(DMF)]·(H₂O) (18), as the original framework, and obtained two isostructures, [Zn2CdO(BTC)₂(DMF)(H₂O)₂]·(H₂O) (19) and [ZnCo2O(BTC)₂(DMF)(H₂O)₂]·(H₂O) (20), by partially substituting cadmium or cobalt centers for zinc centers of polymer 18. Polymers 18-20 show the multifunctional properties in photoluminescence and CH₃OH adsorption. At the same time, polymer 20 also possesses the antiferromagnetic interaction owing to the presence of cobalt centers. In addition, the high-pressure hydrogen storage of polymer 18 has been also examined at 77 K and room temperature.(6) We successfully synthesized three open MOFs, [Cd₃(BDC)0.5(BTC)₂(DMF)(H₂O)]·3(DMF)·(H₃O)·(H₂O) (21)(BDC = 1,4-benzene-dicarboxylate), Cd4(CTC)₂(BDC)(DMF)₂(H₂O)₂·2(H₂O) (22) and Cd4(CTC)₂(BPDC)(DMF)₂(H₂O)₂·2(H₂O) (23) by using mixed two O-donor ligands in the appropriate condition. We analyzed their topology structures as well as examined their thermal stability and photoluminescence properties. To our knowledge, such MOFs constructed from rigid O-donor ligand supporting metal-flexible carboxylate layers have not been still reported so far.(7) In addition, our strategy for preparing novel multifunctional structures is to construct large clustered metal-carboxylate SBUs because although many MOFs built from different SBUs have been synthesized, they usually only comprise of di-, tri- or tetra- nuclear metal-carboxylate clusters. To address this issue, we have synthesized five novel clustered MOFs, [Cd11(μ4-HCOO-)6(bpdc)9]·9(DMF)·6(H₂O) (24), [Zn7O2(pda)5(H₂O)₂]·5(DMF)·4(EtOH)·6(H₂O) (25) (pda = p-phenylenediacrylate),[Zn5(μ3-O)₂(bpdc)₄(DMF)₂(EtOH)₂]·3(DMF)·3(EtOH)·5(H₂O) (26), [Zn4(bpdc)3(bpy)]·2(DMF)·4(H₂O) (27) and Cd₃(bpdc)3(DMF)·5(DMF)·18(H₂O) (28). We analyzed their topology structures as well as studied their thermal stability, photoluminescence, adsorption, hydrogen storage and dye assembly properties. Of particular interest of that polymer 24 with a rare body centered cubic (bcu) topology constructs from an undecanuclear nanosized cadmium cluster, which is the largest transition-metal carboxylate cluster secondary building unit (SBU) reported to date. In addition, these SBUs of polymer 28 are interconnected through biphenyl groups of bpdc to generate a 3D noninterpenetrating extended network with rare etb topology and one-dimensional (1D) hexagonal nanotube-like channels of 24.5 A×27.9 A. To the best of our knowledge, it is the MOF with the largest 1D nanotube-like channels reported so far.In summary, we have focused our study on the influence of the changes caused by the metal ions, organic ligands, chiral solvents and organic amines as templates on the building blocks and structures of MOFs by the solvothermal reaction. We have prepared a series of MOFs with charming topologies, and studied their potential application as multifunctional materials in ion-exchange, adsorption, hydrogen storage along with optics, electrics, and magnetism. We believe that these results would facilitate the exploration of new MOFs with charming molecular topologies and multifunctional properties as well as afford academic bases for directing the synthesis of novel architectures.