Syntheses, Structures And Properties Of Coordination Polymers Based On Azacyclic And Dicarboxylic Ligands

The design and preparation of coordination polymers have attracted much attention in recent years because of their potential applications in gas storage and separation, heterogeneous catalysis, magnetism and optical properties. The organic ligands containing carboxylate or tetrazole groups offer great potentials for fine control over coordination architectures. This thesis describes the synthesis, characterization and properties of a series of metal organic frameworks based on tetrazolate or carboxylate ligands. The main results can be summarized as following six parts:(1) The assembly of asymmetric bis(chelating) 2-pyrimidinecarboxylate (pymc) and 5-(2'-pyrimidyl) tetrazolate (pymtz) with CdⅡproduced three MOFs through the in situ hydrolytic transformation or [2+3] cycloaddition reaction of 2-pyrimidinenitrile (pymCN). In compound 1, the asymmetric of the pymc liangd matches perfectly with the dodecahedral mmmm coordination and the RHO zeolitic topology. The sample evacuated exhibits a typical type I isotherm with no hysteresis, the apparent Langmuir surface area was estimated to be 995m2/g. Interestingly, the crystalline can be recovered by immersing the amorphous sample in water. On the other hand, the pymtz ligands in 2a and 2βprefer the square prismatic or antiprismatic llll coordination, which make the liangds radiate from the metal center in four coplanar directions, resulting to two dimensional square grid networks. To summarize, we have explored the strategy of constructing ZMOFs from eight-coordinated metal ions as "tetrahedral" nodes and bis(chelating) ligands as ditopic linker, the present RHO framework may illustrated a new challenging approach to ZMOFs.(2) We firstly observed the oxalate (ox) through the ring-open reaction of 2-pyrimidinenitrile during the in situ hydrolytic transformation or cycloaddition reaction. To our knowledge, the chemical transformation from pymCN to ox has not been reported yet, although the mechanism is not clear. Interestingly, the magnetic measurements reveal that compound 5 constructed from pymc and ox, exhibiting (6,3) net topology is a spin-canted antiferromagnet with weak ferromagnetic transition below TC=2.4K. In 5, the coordination polyhedron of Mn" is severely distorted due to the small bite angles of the chelating ox and pymc ligands which may lead to the spin canting.(3) Different from the honeycomb [MⅡMⅢ(ox)3]- and [MⅠMⅢ(ox)2(bpym)] sheets constructed from symmetric bis(chelateing) ligands, we firstly reported five neutral honeycomb framework with general formula [NaMⅡ(pymtz)3]n·G. The incorporation of the NaⅠions plays an important role in generating the neutral honeycomb structures:it serves as the bridge between the [MⅡ(pymtz)3]" units, with a perfect match in charge. It is worthy mentioning that solvent-induced transformation of these compounds. The transformation may involves the dissociation of NaⅠinto the solvent, followed by the destroy/rearrangement of the coordination interactions between MⅡand the pymtz ligands. These reactions are solvent selected and may be completed through the dissolution and re-crystallization processes.(4) We get five compounds constructed from 2-methyl-imidazoledicarboxylate ligand. Hydrophobic and hydrophilic channels are formed in compound 19. The preliminary results show that the residual proton can be exchanged by the NaⅠin the sodium hydroxide aqueous solution and the reaction is selected.(5) Twenty-three compounds containing two new topology unprecedented in MOF have been obtained, which are derived from the nitro-functionalized dicarboxylate ligand 2,2'-dinitro-biphenyl-4,4'-dicarboxylic acid (H2DNPDC). (a) We get three compounds containing CuⅡ. Compound 20 features NbO topology based on paddle-wheel second building unit. As expected, the nitro groups, which are ordered on the surface of the channel, impart the surface with higher polarity. Unfortunately, the framework collapses after the guests are evacuated. Magnetically, compound 21, derived from infinite one dimensional copper chains with mixed hydroxo and carboxylate bridges, shows ferromagnetic interactions; 22 exhibits pcu topology net based on tetranuclear copper cluster, in which the CuⅡions are bridged by the mixed hydroxo and carboxylate. Premilary results show that there is antiferromagnetic intratetramer interaction. (b) Using the similar method, two compounds are obtained.23 exhibits two-fold interpenetration pcu net based on the Zn4O(COO)6 unit, while 24 shows four-fold interpenetration dia net based on binuclear CdⅡunit. (b) In the presence of co-bridging pydidyl reagents, we got 11 new coordination polymers. Most intriguingly, compound 36 and 38 are isomorphous with three-fold interpenetrating framework. They display a 4,6-connected three dimensional net, based on mononuclear and binuclear nodes. It is noteworthy that it presents a new topology that has been theorically expected but never been observed in MOFs prior to this work, while 40 is a 6,8-connected and self-catenated net, based on two distinct binuclear nodes.(6) A novel two dimensional coordination polymer consisting of ferromagnetic CoⅡchains with EO-azide and bis(carboxylate) triple bridges exhibit single chain magnet(SCM) behavior. Then another two compounds of NiⅡand MnⅡthat have similar structure display SCM-like and antiferromagnetic features, respectively.