Synthesis And Characterization Of Novel Transition Metal-Dicarboxylate Coordination Polymers

Recently, the design and assembly of coordination polymers have attracted a great deal of interests due to their interesting topologies and potential applications as catalyst, ion exchange, gas storage, superconductor, magnetic, and optical materials. According to the principle of molecular engineering, it is a hot field to design and synthesize the metal-organic coordination polymers with novel topological structures constructed from appropriate metal ions and versatile organic ligands by using either covalent bonds or weaker intermolecular interactions (hydrogen bonding,π…πstacking interaction, etc). Up to now, numerous one-, two-, and three-dimensional coordination polymers have been successfully synthesized. In this paper, we report five new coordination polymers synthesized by different dicarboxylate ligands(H2pam ,H2NDC) and organic amines(en, 1,3-PDA, phen) under hydrothermal condition and characterized by signal-crystal X-ray diffraction, IR, TGA analysis, elemental analysis and their photoluminescent property. Furthermore, we also discuss the effect factors (nature of metal and ligand, temperature) of the final products at hydrothermal condition.1. In chapter two, we choose H2pam, organic amines, transition metal nitrate salt as reaction system at hydrothermal condition and obtained three coordination compounds: [Cu2(C23H14O6)2(C2H8N2)2(H2O)2] (1), [Zn2(C23H14O6)2(C3H10N2)2] (2), [Zn (C23H14O6) (C2H8N2)] (3). Compound 1 exhibits 0-D framework, in which the linkage between the CuII atom and H2pam ligand gives rise to a centrosymmetric cyclic dimer. The en molecule act as a terminal ligand and chelates with CuII atom, and another coordination site is occupied by water molecule. The structure of 2 is similar to 1, in which the ZnII atom links H2pam ligand resulting in a centrosymmetric cyclic dimmer and the 1,3-PDA adopts bidentate chelating coordination mode. There both exist a variety of intramolecular and intermolecular hydrogen bonds in compound 1 and 2, leading to a two-dimensional supramolecular architecture. In compound 3, ZnII atom connects H2pam ligand forming a centrosymmetric cyclic dimmer that are further interlinked by bridging en molecule giving rise to a 2-D layer structure. Compounds 2 and 3 exhibit good fluorescence emissions.Compared with the structures of compounds 1 and 3, compounds 2 and 3 respectively, we can see that we use the same carboxylate ligands and organic amines and the procedure for the syntheses of 2 was the same as that for 1 except that Cu(NO3)2 was replaced by Zn(NO3)2, and in the end we obtained two different frameworks. Compound 1 have 0-D cyclic dimmer, and 3 possesses 2-D layer structure. The en molecule adopts chelating coordination mode in 1 but bridging mode in 3, which leads to the different dimensions of the final products. The syntheses of compounds 2 and three are based on the same carboxylate ligands and metal ion with different organic amines to see the effects of the organic amines in the formation of coordination polymers. Our investigation focus on the synthesis system of en, 1,3-PDA with H2pam and Zn(NO3)2, and we have successfully prepared one new 0-D and 2-D coordination polymers. So we can conclude that the organic amines play two dramatic roles in the reaction: (1) as a agent to deprotonate O-donor ligands; (2) as a ligand to coordinate to the metal ion. Due to the different coordination modes adopted by the different amines, we finally obtain two compounds with different structures.2. In chapter three, we employ H2NDC,phen and cadmium salts as a reaction system under hydrothermal condition by changing the reaction temperature. We have successfully prepared one 0-D {[Cd(phen)3]·NDC·8(H2O)} (4) and 1-D zigzag chain [Cd(NDC)(phen)2?(H2O)]n (5). The remarkable character of compound 4 is three phen ligands chelating to one cadmium atom, which result in the formation of 0-D structure. The coordination sphere of cadmium atom can be described as heavily distorted octahedral geometry, which may result from the huge volume of phen ligand and the big steric hindrance from the coordination of three phen ligands and cadmium atom. There exist free NDC ligands and water molecules. It is found that there are various hydrogen bonds in 4, leading to a two-dimensional supramolecular architecture and are further assembled to form three-dimensional network. In compound 5, it is also very rare that two phen ligands chelates with one cadium atom. The NDC ligand acts asμ2-bridging ligand to connect with two cadmium centers and each cadmium center connects with two NDC ligands to form the zigzag chain. The phen ligands are alternately attached to both sides of the chain. These chains are connected to each other upon hydrogen bonding andπ···πstacking interactions to form three-dimensional network. From the structures of 4 and 5, we found that phen is capping ligand, which decrease the dimension of polymers commonly, and even may lead to the formation of 0-D structures.