Syntheses, Structures And Properties Of Photoluminent Porous Coordination Polymers

Multifunctional metal-organic frameworks (MOFs) that possess porosity and photoluminescence, magnetism, conductivity, etc., have recently drawn great attention because of their potential applications in light-harvesters, chemical sensors and devices. In the construction of these materials, the multidentate organic ligands play a vital role since the structural integrity of these ligands in most cases remains unaltered throughout the assembly process, which helps to realize predesigned structural topology. Up to now, a vast of organic ligands with specified geometry and functionality have been prepared and used in rational synthesis of porous coordination polymers with specific structure and properties. However, directional synthesis and design of MOF materials with specified structures and properties is still a formidable challenge.In this thesis, based on the principle of crystal engineering, we focus our study on the design of ligands with specified geometry and the construction of fluorescent MOFs with interesting structures and multifunctional properties. The purpose of the study is to explore the relationship of structure features and properties of the resulting MOFs. In this thesis, we mainly selected photoluminent multidentate ligands that include alkoxyl carboxylates and BODIPY-based pyridine ligands with combination of metal ions or clusters, to explore the synthesis, topology structures and multifunctional properties of MOFs. Because the use of different ligands in constructing MOFs can offer greater adjustability of structural frameworks and functions than a single ligand, we chose both neutral pyridyl and negatively charged carboxylic ligands in the process of construction of coordination polymers, and produced a number of intriguing MOFs. As results,15 metal-organic coordination polymers were synthesized successfully, and their structure and properties were studied in details.This dissertation consists of six chapters.Chapter 1, Introduction. We gave a brief introduction to the research background and classification of metal-organic coordination polymers.Chapter 2, Two photoluminscent metal-organic frameworks based on a BODIPY-derived bipyridine ligand. We have designed and synthesized two pyridine-substituted BODIPY fluorophores at the 2- and the 6-positions of the indacene core. Both compounds exhibited the general photophysical behavior similar to other BODIPY chromophores. Moreover, they showed highly selective Cu+ sensing properties, and can be used for detecting Cu+ within living cells.Two new metal-organic open-frameworks were solvothermally synthesized by using a photoluminscent BODIPY-based bipyridine linker L, and auxiliary ligands 1,4-benzenedicarboxylate (H2bdc) and 1,3,5-benzenetricarboxylate (H3btc), respectively. MOF1 has a 2-fold interpenetrating three-dimensional framework with body centered cubic (bcu) network, while MOF2 has a highly opened framework with kagome-type net. MOF1 exhibited permanent porosity, while MOF2 was not stable after removal of guest solvent molecules. Both MOF1 and MOF2 exhibited strong fluorescent emissions upon excitation at room temperature. The results show that the use of functional ligand, e.g. organic lumophores, is a convenient method for construction of new coordination polymers with diverse structures and interesting properties.Chapter 3, Construction of three-dimensional metal-organic frameworks in the presence of a tetrahedral ligand and a secondary bidentate linker. Three new open-framework metal-organic coordination polymers were solvothermally synthesized by using a flexible tetrahedral alkoxyl carboxylate ligand (H4L), and semirigid linear bidentate linker (DPE). Compounds MOF3 and MOF4 are isostructural and exhibited permanent porosity. The framework is a 2-fold interpenetrated (4,4)-connected PtS net with the voids filled with coordinated DPE and disordered solvent DMF and water molecules. MOF5 is a uninodal 4-c net with hxg-d topology. The structure was not stable after removal of guest solvent molecules. MOF4 and MOF5 exhibited strong fluorescent emissions upon excitation at room temperature. The results show that H4L is a good candidate for construction of coordination polymers with diverse structures. These compounds not only have intriguing structures, but also exhibit interesting properties.Chapter 4, Synthesis and properties of four coordination polymers built from a semi-rigid tripod carboxylic acid. By using two flexible tripod alkoxyl carboxylate linkers 4,4’,4"-(((2,4,6-trimethylbenzene-1,3,5-triyl) tris(methylene))tris(oxy))tribenzoic acid (H3L-4), eight coordination polymers MOF6-9 have successfully synthesized. Both MOF6 and MOF9 display a 2D hcb-type layered structure, made of an interlocked double-layered sheet and two penetrating single-layered sheets, respectively. MOF7 possesses a (3,6)-connected 3D framework with rutile-related sit topology. MOF8 possesses a polycatenated 3D framework built upon a 12-connecting linear Co7 cluster and a 3-connecting L3 ligand. MOF6 and MOF9 exhibited strong fluorescent emissions upon excitation at room temperature and a selective, efficient emission quenching response towards nitroaromatic explosives. These results indicate that MOF6 and MOF9 are potentially sensory materials for nitroaromatic explosives. The ligand H3L-4 in all the four compounds is 3-connecting from a topology point of view. However, it adopts flexible coordination modes to meet various requirements of different metals, forming new coordination polymers with interesting structures and properties. The preparations of MOF6-MOF9 imply the use of a new, semi-rigid ligand promises the synthesis of a wide diversity of functional coordination polymers.Four isostructural metal-organic frameworks, formulated as [Cd3(L)2(H2O)2]·(DMF)5·(H2O)6(MOF10), [Co3(L)2(H2O)2]·(DMF)2·(H2O)6(MOF11), [Mn3(L)2(H2O)2]·(DMF)3·(H2O)6 (MOF12), [Zn3(L)2(H2O)2·(DMF)5·(H2O)4 (MOF13), have been successfully prepared via solvothermal synthesis based on a semi-rigid ligand 3,3’,3"-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(oxy))tribenzoic acid (H3L-3). MOF10-13 are constructed from a hourglass-like trinuclear M3 cluster and a L3- ligand as secondary building units (SBUs). Each triangular ligand L3- coordinates to three M3 units, while each M3 unit connects six ligands L3-, to form a metal-organic nanocage. MOF10 and MOF13 exhibit strong fluorescent emissions upon excitation at room temperature. And MOF10 also exhibits an interesting fluorescence sensing properties for nitrobenzene compounds. The ligand H3L-3 in all the four compounds is 3,3,6-connecting from a topology point of view. In these structures, the semi-rigid ligand adopts cis,cis,cis-and cis,cis,trans-conformations.Chapter 5, Synthesis of two coordination polymers built from a semi-rigid hexacarboxylic acid. Two new open-framework metal-organic coordination polymers were solvothermally synthesized by using a flexible alkyl amino hexacarboxylic acids ligand (trigonal tri-isophthalate). MOF14 and MOF15 are isostructural and possess a bimodal (4,6)-connected 4,6T4 net.Chapter 6, Conclusions. A brief conclusion on this thesis and an outlook for our future work were given.