Synthesis And Properties Of Coordination Polymers Based On Carboxylate Ligands

Metal-organic coordination polymers have attracted considerable attention due to their intriguing structural motifs and various potential applications in gas storage, catalysis, optics, drug delivery, separation, sensors etc. With current synthesis methods, some problems such as long reaction times, high reaction temperature, use of a large amount of solvent and special apparatus are often encountered, which impede their practical application. Thus, rapid, facile, high-yield routes would be highly desirable. Furthermore, exploration of steady and environmentally benign routes to design and syntheis nano-and micro-scaled coordination polymer particles often remains a significant challenge. In this dissertation, we focus on exploration of new synthetic routes and preparation of new coordination polymers based on carboxylic acids. The main content will be introduced as follows:1. Preparation and characterization of porous nano/micro coordination polymer particles via "carboxylate ammonium salts". When the reaction rate is slow and thus requires high temperatures, the strategy is to convert carboxylic acids into carboxylate methylammonium salts which have high solubility in water.(1) High-quality Cu3(BTC)2(BTC=1,3,5-benzenetricarboxylate) crystals were obtained in water at room temperature by directly mixing aqueous solutions of Cu(NO3)2and the methylammonium salt of H3BTC. By adjusting the concentrations of the two reactants, we could obtain polyhedral crystals (500-1000nm), micro rods (15×3μm) with hierarchical structures and rods (5×1μm) with smooth surfaces. Gas sorption measurements indicate large BET surface areas (1207-1379m2/g) and total pore volume (0.59-0.86cm3/g). Moreover, the unusual combination of micropores and mesopores observed in the micro rods has important prospects in practical industrial processes.(2) CuBDC-1(BDC=1,4-benzenedicarboxylate) was synthesized by mixing aqueous solutions of CuAC2and the methylammonium salt of H2BDC, while CuBDC-2was obtained by mixing water solution of CuAC2with DMF solution of H2BDC. The two compounds were characterized by powder XRD, IR, SEM, TGA and N2sorption measurements. After evacuation at140℃, CuBDC-2has the same structure and properties as CuBDC-1. These results reveal that the remarkable features of "carboxylate ammonium salts" method are operational simplicity, energy-saving and quantitative yields.2. Preparation and characterization of coordination polymers via conventional methods. Four new lanthanide coordination polymers based on carboxylate ligands were synthesized and their structures and properties were investigated.(1) A three-dimensional lanthanide coordination polymer with zeolite ABW topology, Tm(BTC)(DMF)(DMSO), was synthesized under mild condition. Each asymmetric unit contains one8-coordinated Thulium ion. Two centrosymmetric Tm centers link through two chelating/bridging BTC groups to form a metallic dimer. The dimers assemble through carboxyl groups to lead to three-dimensional open frameworks with5x8A2channels along the [100] direction.(2) A three-dimensional lanthanide coordination polymer, Yb3(BDC)4.5(DMF)2(H2O)3·(DMF)2, has been synthesized under mild condition. Each asymmetric unit contains three8-coordinated Ytterbium ions. A ytterbium atom (Yb1) and its corresponding centrosymmtric atom (Yb1A) link through four carboxyl groups of BDC ligands to form an edge-sharing metallic dimer. The dimer assembles with the four metallic monomers (Tb2, Tb2A, Tb3, and Tb3A) through carboxyl groups to form rod-shaped building units, which link each other to lead to three-dimensional open frameworks with5x7A2rhombic channels along the [011] direction.(3) A two-dimensional lanthanide coordination network, Gd(BTC)(phen)(DMF), has been synthesized under mild condition. The asymmetric unit contains one9-coordinated Gadolinium ions. Each Gadolinium atom is connected with three bidendate BTC ligands while each BTC coordinates with three metal centers, forming a two-dimensional layer in the ac plane.(4) A three-dimensional lanthanide coordination polymer, Nd2(suc)3(H2O)2·H2O, has been hydrothermally synthesized. Two adjacent9-coordinated Nd centers link through three carboxyl groups to form a zigzag chain along axis b. The zigzag chains assemble through succinate groups to lead to three-dimensional open frameworks.3. Preparation and characterization of coordination polymers via "carboxylate ammonium salts" method. A series of lanthanide coordination polymers, Ln2(BDC)3(H2O)4(Ln=Y, La, Ce, Eu, Gd, Tb, Ho, Er), including five unknown compounds (Ln=Y, La, Ce, Ho, Er) were synthesized on a large scale in water by converting carboxylic acids into carboxylate methylammonium salts. The products were characterized by powder XRD,IR, SEM, TGA and PL. SEM images reveal that the compounds all exhibit hierarchical architectures in the size range of5-10μm.4. Preparation and Characterization of porous nano/micro coordination polymer particles assisted by monocarboxylic acids. When the reaction rate of metal ions with organic ligands is too fast, the morphology is hard to be controlled. The strategy is to modulate the coordination equilibrium during the growth process by adding different modulators (monocarboxylic acids). The competition between the network linker and modulator could slow down the reaction rate and influence the morphologies of the resulting coordination polymers. By adding seven different modulators into the reaction system at room temperature, Cu3(BTC)2spheres (50-200nm) and polyhedrons (400nm-3μm) were successfully obtained. The products were characterized by powder XRD, IR and TGA. N2sorption measurements reveal large BET surface areas (1087-1273m2/g) and total pore volumes (0.60-0.73cm3/g).