Synthesis,structures And Catalytic Performance Of Transition Metal-carboxylate Coordination Compounds

Coordination polymers and materials have attracted great attention in the field of inorganic and materials chemistry due to their customable structures and diverse functional properties.In the past few decades,coordination polymers have been widely used as functional materials,including adsorbents,sensors and probes,catalysts and biologically active composites.Investigation of organic reactions using metal complexes or coordination polymers as catalysts has attracted great attention in recent years.Such model catalytic processes include the Henry reaction,hydrogenation of aldehydes and ketones,oxidation of alkanes and alcohols,and coupling of CO₂ with epoxides.Considering a sustainability perspective,there is an important trend to develop heterogeneous and reusable catalysts composed of inexpensive metal centers and capable of providing high catalytic activity under mild conditions.In this thesis,two carboxylic acid ligands were selected,namely 3,2',4'-biphenyltricarboxylic acid and 2-chloroterephthalic acid,which were rarely used for the synthesis of coordination polymers.The combination of these carboxylic acids as main building blocks with metal(II)ions and a series of auxiliary ligands under hydrothermal conditions,resulted in the isolation and full characterization of 17 new coordination compounds.Their catalytic performancees were also studied in two model reactions.Chapter 1:This chapter briefly introduces the main concepts of coordination chemistry and crystal engineering,summarizes various synthesis methods and factors that affect the structure of coordination polymers,and discusses the properties of such coordination compounds in terms of fluorescence behavior,gas adsorption,molecular magnetism and application in catalysis.Chapter 2:Reaction mixtures composed of 3,2',4'-biphenyltricarboxylic acid(H₃bta)as the main ligand,transition metal ions(Cd(?),Ni(?)and Zn(?))and auxiliary ligands(2,2'-bipyridine,4,4'-bipyridine,1,10-phenanthroline,pyridine,or 2,2'-biimidazole)were reacted under hydrothermal conditions to obtain 9 transition metal coordination compounds with novel structures.The crystal structures and thermal stability were determined by single crystal X-ray diffraction,and supported by standard characterization techniques including elemental analysis,PXRD,FTIR,TGA,and fluorescence spectroscopy.Analysis of the structural characteristics of the obtained compounds 1–9 shows their diversity,including one-dimensional chains,two-dimensional layers,and three-dimensional frameworks.The solid-state emission properties of the selected products were also investigated.The synthesized compounds 1–9 were used as catalysts to promote the cyanosilylation reaction of aldehydes with trimethylsilyl cyanide to give cyanohydrin derivatives.Among them,the complex 3 exhibited a particularly high catalytic activity when using 4-nitrobenzaldehyde as a model substrate,with the yields as high as 96%.In addition,the effects of reaction time,type of solvent,substrate range,catalyst loading and recycling on the yields of cyanohydrin products were investigated.Chapter 3:Reaction mixtures comprising 2-chloroterephthalic acid(Clta H₂)as a main ligand,transition metal ions(Cd(?),Zn(?),Cu(?)and Co(?))and auxiliary ligands(2,2'-bipyridine,4,4'-bipyridine,1,10-phenanthroline,bis(4-pyridyl)amine,or 2,2'-biimidazole)were subjected to hydrothermal synthesis,resulting in 8 new coordination compounds 10–17.Their composition,thermal stability and structures were studied by standard methods,including elemental analysis,FTIR,TGA,PXRD and single crystal X-ray diffraction.Analysis of the structural characteristics of the compounds indicates that the structures of10–17 are highly diverse,ranging from one-dimensional chains(14 and 17)to two-dimensional layers(10–12)and three-dimensional metal-organic frameworks(13,15 and16).The solid-state emission properties of the selected products(Clta H₂,13?14?16 and17)were also investigated.The complexes 10–17 were used as catalysts to catalyze the coupling reaction between CO₂ and epoxides.One of the complexes 13 revealed a particularly high catalytic activity in coupling of epichlorohydrin and CO₂ to produce the corresponding cyclic carbonate in up to 71%yields.In addition,the effects of different reaction parameters,including substrate and catalyst loadings,catalyst recycling,and solvent type were also examined.