Design And Synthesis Of Molecular-type Complexes Based On Supramolecular Interaction For Catalysis And Humidity Sensitivity

With the increasing greenhouse effect and atmospheric pollution are seriously affecting industry and people’s daily life,so it is particularly necessary to develop materials for CO₂ catalytic conversion and environmental detection.Previous functional materials have limited their performance because of size effect.Therefore,functional materials with single molecule as structural unit have become a hot topic in the research field.Among them,the molecular-type complex has been drawing much attention in energy catalysis and environmental detection,due to their structural characteristics（uniform and clear active sites）and controllability.However,molecular-type complex has problems such as harsh reaction conditions and difficult separation when used as catalysts,and disadvantages such as low sensitivity and poor stability when used as sensing materials.Therefore,in this paper,nine novel molecular-type complexes were prepared by structure designing and optimizing of complex through ligand tuning strategy.The results show that these molecular-type complexes can efficiently catalyze CO₂ cycloaddition reaction and Knoevenagel condensation reaction under green and mild conditions,and show excellent performance in humidity detection.The main research results are as follows:（1）The effect of supramolecular interaction in the catalyst on the catalytic performance for CO₂ cycloaddition reaction was investigated.Four 4f molecular-type complexes were synthesized by metal center substitution and ligand tuning strategy.The selection of lanthanide metal center makes these complexes have more coordinated water molecules,and the regulation of carboxylate ligand achieves an increase in the number of hydrogen bonds from Ho-1 to Sm-2,Tb-2 and Ho-2（Ln-2 series）,which significantly improves their catalytic activity and stability as catalysts in CO₂cycloaddition reaction.Under solvent-free condition at near room temperature for reacting 12 h,Ln-2 series can obtain more than 90%yield.Kinetic studies show that reaction activation energy of catalyst Tb-2 is the lowest compared with Ho-1.（2）The effect of the difference in electron density of the active center in the catalyst on the catalytic performance for Knoevenagel condensation reaction was investigated.Three erbium molecular-type complexes were synthesized in one step by ligand tuning strategy.The electron-donating ability ligand was selected to replace the coordinated water molecule in Er-1 structure to form Er-2 and Er-3,and the resulting charge transfer effect converts the Lewis acid-base sites into electron-rich active sites.These catalysts exhibit excellent catalytic performance in Knoevenagel condensation reaction.The complex Er-2 can obtain the TOF（turnover frequency）value of up to 440h^-1 under solvent-free condition at room temperature,as well as wonderful cycling stability and substrate universality.（3）The performance and application of molecular-type complex in humidity detection were investigated.Two low dimensional molecular-type complexes Pb-1 and Co-1 were prepared by in situ self-assembly of metal ions and organic ligands.Among them,Pb-1 exhibits ultra-high sensitivity in humidity monitoring,with the response value as high as 1.18×10⁴ and the response time as short as 2 s.The humidity sensor based on Co-1 shows great application potential,especially for monitoring the moisture content of human finger skin,with extremely short response-recovery time（1 s and 3s）,as well as outstanding stability and repeatability.