Assembly Of Polyoxometalates Ionic Frameworks And Their Highly Selective Gas Adsorption And Separation

The frameworks recived widespread attention and achieved considerable development in recent years because that they have large specific surface areas and a variety of structure types,and can be widely used in the fields of catalysis,adsorption,and separation.Except the metal-organic frameworks based on coordination bonds and the covalent organic frameworks based on covalent bonds,the ionic framework s based on electrostatic interaction between anions and cations are also an important type of frameworks.Under specific conditions,a variety of cations and anions can be combined to form an ionic frameworks with appropriate force.As a kind of important inorganic clusters,polyoxometalates(POMs)have the characteristics of multiple structures and abundant properties,and are an important type of supermolecular assembly building elements.Organic components covalently modified on polyanion can combine organic components and inorganic components through covalent bonds.The obtained organic-inorganic hybrid products not only enrich the structure type of POMs,but also expands their functions applications.As an important class of organic compounds,triol ligands can be applied for modification of different types of POMs,such as Anderson,Lindquist,Keggin,and Dawson types.Up to now,for the triol ligand modified Anderson-type POMs,the related research work has mainly focused on the discovery of new cluster structures and functionalization based on organic functional groups,and the design and utilization.And little work has been done on construction ionic framework using this type of polyanions as building blocks.In this thesis,the triol ligand modified Anderson-type POMs with divalent transition metal ions as the central heteroatom were used as the building blocks.In aqueous solutions,compounds with 1D,2D and 3D structures were achieved by selecting different counter cations.The single crystal x ray diffraction,powder x ray diffraction,elemental analysis,and infrared spectroscopy were used to analyze the structure and composition of the obtained compounds in detail.The thermal stabilities of the compounds were characterized by TGA.According to the structures,compositions and thermal stabilities of different compounds,the corresponding electrochemical properties,magnetic properties and gas adsorption properties were further studied.Specific research work includes the following three aspects:1.With 2-aminopyridine as counter ion,by using the hydrogen bonds between cation and polyanions,the triol-ligand modified Ni-centered Anderson POMs were ordered arranged in a 2D plane.Comparative experiments show that this planar hydrogen-bonded donor can also induce unmodified polymolybdate to form a 2D structure,indicating that the cation has a certainuniversality for inducing the planar arrangement of polyanions.2.A series of triol ligands modified divalent metal ion centered Anderson-type POMs with different counter cations were synthesized by using a conventional beaker method.The single-crystal X-ray diffraction results show that when the counter ion is ammonium,each polyanion exists in a discrete structure.At this condition,the triol ligand can be modified on the cluster in different forms.When the counter ion is replaced by copper ion,it acts as a bridge to connect two adjacent polyanions to form a 1D chain structure.When the counter ion is sodium ion,a two-core and a four-core cluster can be formed,which can be used as connection points to connect the surrounding polyanions to form a 2D planar structure.3.When the reaction solvent is changed from water to a buffer solution of HAc/Na Ac,the 3D structure of the triol-functionalized Anderson type POMs can be obtained.At this time,the counter ions of the compound are sodium ions and ammonium ions,and the former serves as a connection point to connect three adjacent polyanions.In these compounds,the heteroatoms of the POMs can be iron,cobalt,nickel,copper,and zinc,indicating that the method has certain universality.Gas adsorption experiments show that these compounds have strong selective adsorption capacity for carbon dioxide,but weak adsorption capacity for nitrogen,methane and hydrogen,which can be used as potential gas separation agents.The above research work shows that the cation in the compounds has important effects on the assembly structure of POMs.The ordered arrangement of anions can be achieved by replacing the cations,and then new functional characteristics can be developed according to the structural characteristics of the ordered assemblies.