Hydrothermal Synthesis Of Metal-Organic Frameworks Based On Imidazoledicarboxylate And Its Derivatives

Metal-organic coordination polymers, a new kind of functional molecule materials, have attracted much more attentions for their flexible tailoring, various topologies and promising application in ion-exchange, adsorption, molecular recognization, catalysts along with optics, electrics, magnetism and enantioselective separation. 4,5-imidazoledicarboxylic acid(4,5-IMDC) has multiple coordination sites for rigid and stable higher dimensional structures. In particular, 4,5-IMDC is a proton donor, it can be partially or fully deportonated to generate H2IDC-, HIDC2- and IDC3- at different pH values, therefore it provides various acid–base type coordination modes. Of most significance is the arrangement of the two N atoms with the N–X–N angle of about 144o (X = center of the imide ring), which is very close to the Si–O–Si angle of 145o in zeolites. Accordingly, it is sure more new novel metal-organic frameworks will be synthesized using 4,5-IMDC or its derivatives as ligands. The 4,5-Imidazoledicarboxylates derivatives have a smaller substituent such as a methyl or ethyl group at the 2-position, it may be lead to form some new structures. A series of metal-organic frameworks have been hydrothermally synthesized by using 4,5-IMDC and its derivatives 2-methyl-4,5-imidazoledicarboxylic acid (2-MeIMDC) and2-ethyl-4,5-imidazoledicarboxylic acid (2-EtIMDC) as ligands. In chapter two, employed 4,5-IMDC as a bridging ligand, three coordination polymers were prepared and structurally characterized: (1) In the structure of compound 1, it contains two different one-dimensional(1D) chains. The Cd(1) atom is six-coordinated forming a octahedron [CdNO5] unit. The Cd(2) atom is seven-coordinated forming a [CdNO6] unit. The [CdNO5] unit and the [CdNO6] unit are connected together to form an interesting 1D zigzag chain along b-axis. The zigzag chains are further connected by the ligands to form a 2D layer in the ab plane. The Cd(3) atom is six-coordinated forming a [CdN2O4] unit. The ligands link the [CdN2O4] units via b-axis to form a 1D chain. The adjacent 2D layers are parallel with each other and construct a 3D framework through the 1D chains via c-axis.(2) Compound 2 is a 0D metal-organic framework containing Co4 molecular squares with 4,5-IMDC bridges.(3) Compound 3 possesses a 1D zigzag chain structure built from Cd(II) centers and the 4,5-IMDC ligands, the adjacent chains are held together by hydrogen bonds between water molecules and all four unique carboxyl O atoms, thus generating a 3D network.In chapter three, Mn(H2O)2(C6N2O4H5)2 (4), [KCd(C7N2O4H5)](5) were prepared and structurally characterized under hydrothermal conditions by using 2-MeIMDC and 2-EtIMDC as bridging ligands:(1) Compound 4 shows a 3D supramolecular framework. The Mn atom lies on an inversion center and forms a slightly distorted octahedral unit [MnN2O4]. The [MnN2O4] units connect each other through hydrogen bonds forming the 1D chain. These chains are held together by hydrogen bonds between water molecules and two carboxyl O atoms, thus generating a 3D network.(2) Compound 5 is a 3D framework with a 1D channel along c-axis. The 1D channel is constructed by four 1D chains, and the K+ are located in the channels.