Syntheses,Structures,And Properties Of Coordination Polymers Based On Ligands Containing Nitrogen And Oxygen Atoms

Coordination polymers（CPs） constructed from metal ions and multifunctional organic ligands as an important class of solid–state materials have shown potential applications in photoelectron materials, gas–storage, magnetic materials and catalytic properties. The research of coordination polymers has attracted current attention in inorganic, solid state chemistry, and materials science. The choice of organic ligands is flexible and metal ions have abundant properties of optical, electrical and magnetic which make CPs display synergistic performance of organic and inorganic components. The synthetic methods of coordination polymer is versatile and strategic.Among them, the in situ synthesis method is an effective way to synthesize coordination polymers due to following reasons: in situ synthesis method is one of the most promising methods to reduce the synthetic steps and maintain system complexity. Meanwhile, new CPs constructed from organic ligands which are otherwise inaccessible from conventional synthesis can be isolated through in situ ligand formation. We focus on the solvothermal synthesis to assemble ligand and transition metal ions into novel CPs. Factors deciding coordination ability and coordination mode of ligands via in situ oxidative dehydrogenation have been studied systematically. Crystal structures of as–prepared CPs have been determined by X–ray diffraction method and their properties are investigated. The thesis contains four chapters:The first chapter introduces the background and applications of the CPs.The second chapter introduces the synthesis and characterization of a new tripodal ligand 4–（3,5–（dicyano–2,6–dipyridyl）dihydropyridyl）benzoic acid（HL₁）synthesized through Yamagushi’s reaction. Based on HL₁, eight coordination polymers formulated as {[M（L₁）₂（H₂O）₂]?4H₂O?2DMF}_n（M = Co（1） and Ni（2））,{[Cd（L₁）]?Me OH?3DMA}_n（3）, {[Co(L_1a)₂（H₂O）₂]?2H₂O}_n（4）,{[Co(L_1a)₂（H₂O）₂]?4H₂O}_n（5）, {[Co(L_1a)₂（H₂O）₂]?6DMF}_n（M = Co（6） and Cu（7））,{[Cu₂(L_1a)₂]?6DMF}n（8）（HL₁a = 4-（3,5-dicyano-terpyridyl）benzoic acid）. Ligand L₁-in compounds 4–8 underwent in situ oxidative dehydrogenation and resulted in L_1a-,which is capable of forming novel compounds 4-9 via self–assembly with various metal ions. The two isomorphous transition metal compounds 1 and 2 feature two-dimensional（2D） layered structures. The Co（II） centres are joined through the scaffolds of L₁- ligands, leading to the formation of a 4⁴–sql coordination layer, which further form the three–dimensional（3D） frameworks through the hydrogen bonds.Uncoordinated pyridyl groups pointing up and downwards the 4⁴–sql layers are observed, which act, together with the dihydropyridyl N–H groups and aqua ligands,as potential binding sites for guest water and DMF molecules involved in the 3D hydrogen bonded network structure. As a representative, the variable temperature powder diffraction of compound 1 has been studied to determind the possible solid–state in situ ligand transformation. In the structures of compounds 1 and 4,ligands L₁- and L_1a- exhibit a similar coordination mode with monodentate carboxyl group and single pyridyl group participating in coordination with two octahedral Co2+ions. Compound 5 is a 2D layered stucture. The interesting hydrogen-bonded octanuclear water cluster is observed between the 2D layers. These solvent water molecules link the 2D layers to form the 3D supramolecular framework. Considering the cubic water cluster as 8–connected nodes, and Co2+ centers and L_1a- ligands as4–connected nodes, the structure of 5 can be viewed as a 3D 3–fold interpenetrating4,8–connected binodal flu net. The formation mechanism of L_1a- ligand via in situ oxidative dehydrogenation reaction has been briefly discussed.In the third chapter, in situ ligand transformation was introduced into a complex mixed ligand system. One novel coordination polymer, namely, [Co₃（μ₃–OH）₂(L_1a)₂（TP）（H₂O）₂]_n（9）, was synthesized through solvothermal reaction. The formation conditions, structure and property of compound 9 are carefully studied and discussed.The rule of in situ ligand transformation is summarized. This current study confirms that in situ ligand transformation is viable for controlled coordination polymerassembly, and is also adaptable to a more complexed ligand system.The fourth chapter summarizes the work and perspectives of this thesis.