Synthesis, Structure And Properties Of Picolinic Acid Microcellular Coordination Polymers

Porous coordination polymers are porous, crystalline compounds with periodic network structures constructed by self-assembling metal ions/clusters with bridging ligands, which have emerged as a new category of porous materials that have intriguing structures and diverse applications. Even though the early discovery of new porous coordination polymers appears to be serendipitous, much effort has been made to reveal their structure-property relationships for the purpose of rational design of novel frameworks with expected properties. Until now, it will be a great challenge to rationalize the synthesis of functionalized porous coordination polymers. This dissertation was focused on the construction of porous pyridyl-carboxylate coordination polymers by using reduced symmetry ligands, in which some relating aspects were discussed, such as the effect of the pyridyl groups on the structure and properties; explore the suitable synthesis strategy for coordinating the function of pyridyl and carboxyl groups and combining their advantages in one structure to prepare more excellent porous material than those based on either carboxylate or pyridine ligands; the using of reduced symmetry linker to construct highly symmetrical frameworks. Based on the above ideas, a series of porous coordination polymers have been synthesized and characterized by the pyridyl-carboxylate or imidazole-carboxylate mixed ligands.There are five chapters in the dissertation:Chapter 1 gives a brief introduction of the background, the developing history, the design principles and potential application, as well as the coordination polymers based on pyridyl-carboxylate ligands, and the research motivation and advances of this dissertation. Chapter 2 introduces four amine-functionalized microporous coordination polymers based on the imidazole-carboxylate mixed ligands. Two of which are isostructural and show 6-connected self-penetrating nets, as well as exceptional water stability and high selectivity for CO2. Furthermore, by employment of positional isomeric ligands, two isomeric flexible frameworks were successfully prepared, which displays the important role of the substituent groups on tuning the structural characteristics and sorption functions, and presents a good case for the difference between isomeric frameworks.In Chapter 3, four microporous coordination polymers were constructed from an unsymmetrical pyridyldicarboxylatic acid and N-donor ancillary ligands, with varying porous sizes, shapes, pore volumes and voids ratio distributing between the pores. In addition, two isomeric microporous frameworks based on the same reactants controlled by solvent systems have been successfully prepared. Interestingly, the coordination modes of all the ligands and metal centrals are the same in the two compounds. The different orientations of the ligands lead to discrepancies in structure and thermal stability, as well as great difference in gas adsorption. The case is an important example showing quite different behaviors based on framework isomerism. More importantly, gas adsorption studies for those compounds indicate that they all possess high selective adsorption of CO2 over N2.Chapter 4 presents two novel 3D microporous coordination polymers, which exhibit high gas adsorption capacities for N2, H2 and CO2. In particular, the frameworks show uncommon multistep gas adsorptions with hysteretic desorption, which reveals an interesting dynamic behavior and breathing effect. Moreover, they both show excellent CO2 adsorption selectivity and capacity with low apparent adsorption enthalpy. On the other hand, the system presents a very rare example that the thermal stability of the framework constructed from paddle-wheel Zn2 units is higher than the structure based on the Cu2 units.Chapter 5 reports four unusual Ln-MOFs with unprecedented nanocages. Among them, the Eu-based compound reveals high luminescent selectivity and sensitivity for Cu2+ ion resulting from weak contacts between pyridyl sites in L4- and Cu2+ ions, as well as selective capture for CO2.Finally, a brief summary of this work is given.