Synthesis And Characterization Of Novel Carboxylic Ligands And Metal-Organic Frameworks

Metal-organic frameworks (MOFs), also known as coordination polymers, are crystalline coordination-based compounds in which metal centres are bridged via organic multitopic ligands to form multi-dimensional networks. The synthesis of MOF always begins with selection of the two maininteracting components-:the metal centres or the metal clusters and the bridging organic ligands. Nowdays, non-conventional in situ synthesis and conventional organic synthesis are the common ways of designing and preparing organic ligands. In the former ligand precursors are modified in situ to give organic ligands which are subsequently linked to the metal centres. This procedure may involve hydroxylation, decarboxylation, alkylation and hydrolysis, among others. In conventional synthesis the organic ligands are prepared, step-by-step, from organic precursors and the resulting compounds are later employed in the self-assembly of MOFs.After theoretical study on the influence of the ligand on the synthesis of metal-organic frameworks, we designed and synthesized a series of nonplanar aromatic multi-carboxylate ligands with a big rigid structure (H3L3, H3L4, L5, H2L6, H2L7, L8, H4L9, H4L10). Eight novel MOFs were obtained through the assembly reactions between the synthesized ligands and Zn2+, Cd2+, Cu2+. All complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, thermal analysis, XPRD analysis, fluorescence spectroscopy, and gas adsorption. The contents of this dissertation are as follows:1. Three new metal organic coordination compounds,[Cd (L2)2]·4.5H2O (1),[Zn(L2)2·(H2O)2]·0.5H2O (2) and Cu(L1)2(3),(L2=3-chloro-2-(5H-tetrazol-5-yl)pyridine; L1=3-chloropicolinic acid), have been hydrothermally synthesized, in which, L2and HL1were synthesized via in situ reaction. MOF-(1-3) shows diverse structures by changing from a zero-dimensional cluster to1D chain to2D44layer. The changes in structure result from the different bridging abilities of tetrazolate ligands. Weak interactions, such as hydrogen bonds and halogen bonds, play important role in the construction of metal-organic frameworks.In addition, three complexes display modest thermal stability and compound1and2show strong solid-state fluorescent emissions.2. A3D (12)4(12)3coordination network with high topological density and extremely tight self-catenation of12-rings has been obtained based on [Cu2(COO)4] paddlewheel SBUs and a tripodal carboxylate linker. The self-catenation is " strong" i.e., the network cannot be transformed into an array of interpenetrating nets by breaking any chemical bond. To the best of our knowledge, MOF-6has the highest topological density among all known3,4-coordinated nets.4. Five different silicon-based ligands have been designed and synthesized. We synthesize and characterize five different novel metal-organic frameworks. The solvent system plays an important role in modulating the final structures. Complex5and8present3D double-interpenetrating network. Complexes4and7show the noninterpenetrated frameworks.