Synthesis,Structural Transformation And Properties Of Aluminum-Oxo Clusters

Metal wheel clusters have always been the focus of coordination chemistry due to highly symmetric structure and special properties.It has the advantages of diverse structure,modifiable structure,adjustable size,etc.,which has attracted wide attention of researchers.At present,a large number of transition metal and lanthanide wheel clusters have been reported.However,the research progress of the main group elements is slow.As the representative of the main group element,aluminum is rich in the earth.Its natural abundance determines the diversity of its compounds and the universality of its application.Therefore,it is of great value to simulate the formation process of aluminum-oxo clusters（Al OCs）in nature.Aluminum-oxo cluster chemistry is a very important research field in metal oxide cluster chemistry,which closely intersects with many disciplines.As a new kind of material,the further promotion and development of cluster chemistry,structural chemistry,coordination chemistry and other related subjects,and provides an effective molecular model to reveal the relationship between the structure of a substance and its corresponding properties.However,due to the easy hydrolysis,the study of Al OCs is still in its infancy.The synthesis of Al OCs with clear structural information remains a major challenge.At present,the structure type of Al OCs is relatively simple,especially,the assembly of aluminum-oxo wheel clusters has not been reported.Therefore,this paper aims to design and synthesize Al OCs with novel structure types and high symmetry,and pay attention to the functional modification of their structures,so as to further study the structure-activity relationship between structure and properties.In this paper,a series of novel aluminum-oxo wheel clusters were successfully designed and synthesized by means of delayed coordination hydrolysis under solvothermal conditions.The coordination assembly chemistry was studied in detail from the perspective of structure,and the aluminum-oxo wheel clusters were used as secondary building units to assemble the porous materials.The research content is mainly divided into the following three parts:（1）Adjustment of wheel clusters size:A series of novel aluminum-oxo wheel clusters with adjustable structure were designed and constructed for the first time by means of delayed coordination hydrolysis strategy,and the coordination assembly chemistry of Al³⁺was studied in detail at molecular level.Monohydric alcohol as a structure-directing agent can effectively control the size of the wheel clusters.Among them,Al₁₆ is the highest-core aluminum-oxo wheel cluster currently reported.In addition,the benzoic acid ligand protected on the periphery of the cluster core can not only be functionally modified by a one-step reaction,but also can be replaced by a stepwise assembly.（2）Structural transformation of wheel clusters:In order to further enrich the structural types of aluminum-oxo wheel clusters,aliphatic carboxylic acid ligands with less steric hindrance are introduced.With the aid of monohydric alcohol and glycol,a series of Al₁₀ clusters with the same cluster core but different configurations were successfully synthesized.The Al₁₀ modified by monohydric alcohol is"coplanar",and the cluster core were twisted to form"saddle shape"after the introduction of diols with more abundant coordination site.Interestingly,the saddle-shaped Al₁₀ can be transformed into a coplanar Al₁₀ through structural transformation,and the density functional theory calculation proves that the structural transformation process is thermodynamically spontaneous.（3）Coordination and assembly of wheel clusters:We designed and successfully separated the{Al₈}wheel clusters coordinated by niacin,and used its empty N coordination sites to further assemble with heterogeneous metals,two copper-doped frame materials based on{Al₈}structural units were constructed.During the synthesis process,we found that the use of alkaline modifiers has a greater impact on the structure of the copper halide cluster nodes.In addition,the doping of copper halogen clusters greatly reduces the band gap of the compounds,indicating that these materials can be used in photocatalytic research.This study not only makes the self-assembly of Al OCs reach a new height,but also provides new ideas for the performance research of Al OCs.