Research On The Properties Of Cucurbit[n](n=5?6) Urils And Heteropoly Acids Self-assembly

Cucurbit[n]urils?Q[n]?,is a new type of cage-like compound with the bridge of n glycine units and 2n methylene groups.The hydrophobic cage cavity of Q[n]can bind organic molecules or ions and the negatively charged polar carbonyl oxygen atoms can coordinate or ion-dipole with metal ions or positively charged groups.The positive surface of Q[n]can interact with anions or negatively charged groups.Therefore,the Q[n]chemistry has become a new research hotspot.Heterpolyacids?HPAs?,also known as polyoxometalate,is acidic and oxidative reductive.It has a good application prospects in the fields of catalysis,separation,identification,and adsorption.Due to the good solubility of heterpoly acids,it is difficult to be separated from the product,difficult to be recycled,and cannot be reused.Therefore,it is also one of the research hotspots in the field of HPAs chemistry to select the appropriate carrier to support heterpoly acids and make it become a solidheterpoly acids material with stable properties.According to the literature reports and the preliminary work of the research group,the driving force of the outer-surface interaction between Q[n]-HPAs is the interaction between cucurbit and polyacid anions.The self-assemblies of Q[n]and HPAs can obtain a self-assembly that is difficult to be dissolved in water,acid solution,alkali solution or organic solvent.The self-assembly system is easy to prepare and stable in nature,not only maintains the original structural characteristics of Q[n]and HPA),but also maintains the functional properties of HPAs.It is a new type of supported HPAs material.In this paper,Q[6]and Keggin type HPAs,H₃PMo₁₂O₄₀(PMo₁₂),H₃PW₁₂O₄₀(PW₁₂)and H₄SiW₁₂O₄₀(SiW₁₂),are selected as building blocks.The structural and functional properties of self-assembly of series Q[6]-HPAs were investigated.The main research contents are as below:Q[6]and Keggin type HPAs,H₃PMo₁₂O₄₀(PMo₁₂),H₃PW₁₂O₄₀(PW₁₂)and H₄SiW₁₂O₄₀(SiW₁₂),are selected.The self-assembly of series Q[6]-HPAs was characterized by powder diffraction,scanning electron microscopy,energy spectrum and elemental analysis.The self-assembly of series Q[6]-HPAs was used to catalyze the synthesis of propyl gallate.The effects of catalyst dosage,reaction time,molar ratio of acid and alcohol on the yield of propyl gallate were investigated.The results showed that the self-assembly had a good catalytic effect on the synthesis of propyl gallate,among which the yield of Q[6]-SiW₁₂,Q[6]-PW₁₂,Q[6]-PMo₁₂2 was 94.71%,88.74%and83.96%respectively.It can be used as heterogeneous catalysis for esterification and other reactions.Q[5]and ammonium molybdate[?NH₄?₆Mo₇O₂₄,N₆Mo₇]were selected for self-assembly to form a stable Q[5]-N₆Mo₇ supramolecular self-assembly.The structure was characterized by infrared spectroscopy,energy spectrum,X-ray single crystal diffraction,X-ray powder diffraction and other methods.The recognition of metal ions in solution by Q[5]-N₆Mo₇ self-assembly was investigated.The experimental results showed that Q[5]-N₆Mo₇ self-assembly can be used to trap and recover rare earth metal ions in solution,and can selectively identify Fe³⁺and Hg²⁺in solution.