Hydrothermal Synthesis, Structure And Properties Of Novel Coordination Polymers Generated From 1,2,4-Benzenetricarboxylate And Organosulfur Ligands

The construction of metal–organic frameworks (MOFs) based onmetal-ligand coordinative covalent bonding is of great interest, mostlymotivated by their intriguing structural features and enormous range ofapplications in catalysis, adsorbent and molecular recognition. Compared withthe formation of inorganic porous materials such as zeolites and metalphosphates, MOFs can be designed and constructed to generate cavities orchannels of various sizes and shapes through control of the architecture andfunctionalization of the organic linkers. However, to date, the precise predictionof a MOFs with a chiral or noncentrosymmetric framework employed in thesecond-order nonlinear optical effects is still a daunting task, because theformation of such a framework is governed by many factors such as possiblenoncovalent intermolecular forces, the solvent, reaction composition, the type oftemplates used etc. The control of framework chirality or noncentrosymmetry isparticularly difficult. Thus, many work need to be done.Recently, a series of noncentrosymmetric MOFs based on metalpyridinecarboxylates have been obtained. It seems that the unsymmetry of theorganic ligands can be transferred to the certain building units of thosecompounds, which can futher connect to each other by organic ligands to formnoncentrosymmetric topologies and maintain the original unsymmetry. Toexplore the synthetic strategy of noncentrosymmetric MOFs, we extended ourresearch into the metal/unsymmetric bridging carboxylate and organosulfurligand system. As a result, ten compounds have been prepared, four of whichhave noncentrosymmetric topologies.In chapter two, employed 1,2,4-benzenetricarboxylate (1,2,4-BTC) as abridging ligand, three novel 3-D coordination polymers were prepared andstructurally characterized. In the structure of the compound 1, the sixfoldcoordination of Na corresponds to a slightly distorted triangular prism. Theinfinite Na-O chains are connected one to each other by sharing vertices of thedimers of Zn to build inorganic planes with strong bonds. The organic ligand,1,2,4-BTC, shows a novel and unprecedented coordination mode: 11 bonds to10 metals with each carboxylate function exhibiting different linkages. Itremains stable when desolvated and when heated up to 410 oC. Its structure ofcompound 2 contains two-dimensional inorganic cadmium-oxygen layers, whichare further linked by 1,2,4-BTC ligand into a 3-D supramolecular framework.The 1,2,4-BTC ligand also shows a novel coordination mode: 9 bonds to 8metals with each carboxylate as a tridentate group. The compound exhibitsintense photoluminescence at room temperature and shows distinct NLOproperties. It remains stable when desolvated and when heated up to 380 oC. Inthe structure of the compound 3, 1,2,4-BTC ligand links the tetranuclear cobaltclusters into a 3-D supramolecular framework. Magnetic measures reveal thatthis compound shows canted antiferromagnetism below 48.0 K.In chapter three, three novel 2-D coordination polymers were prepared. Itsstructure of compound 4 contains two different one-dimensional (1-D) chainsfor the Cu ions, namely [Cu2(1,2,4-BTC)2]n2n-and [Cu(4,4′-bipy)]n2n+;thecarboxylate of 1,2,4-BTC ligands links the two different 1-D chains into ainteresting steplike neutral framework. In compound 5, its structure containsnovel paddle-wheel clusters Cu2(CO2)4(4,4′-bipy)2 as SBUs which are furtherlinked by monoprotonated 1,2,4-BTC ligands into a 2-D neutral framework. Theadjacent 2-D layers are parallel with each other and construct a 3-D frameworkvia the vander waal's forces. The magnetic studies for compound 4 and 5 show adominant ferromagnetic exchange between the Cu(II) ions. Its structure ofcompound 6 contains one-dimensional In-O-In-O-chains, which are furtherlinked by 2,5-PDC ligands into a 2-D supramolecular neutral framework. Theadjacent 2-D layers are parallel with each other and construct athree-dimensional framework via the hydrogen bands. At room temperature, thecompound exhibits intense photoluminescence. On the basis of the results ofTG/DTA analyses, the structure is thermally stable up to ~ 390 ?C.In chapter four, using unsymmetrical bridging organosulfur ligand, four3-D supramolecular coordination polymers were prepared. Compound 7contains zero zinc units, which are further linked by vander waal's forces into a3-D supramolecular framework. Compound 8, 9 and 10 contain similarone-dimensionsal chains, which are further linked by vander waal's forces into a3-D supramolecular framework. In this system, they don't have H-bonds or π –π interactions. At room temperature, the four compounds exhibit intensephotoluminescence owing to the π* → n transitions of the organic ligand.