Synthesis And Properties Of Coordination Polymers Based On Rigid Pyridinecarboxylic Acid Ligands

Rigid pyridinecarboxylic acid ligands have became a hot area of research because of the good largeπconjugated surface,various coordination modes,adjustable deproton ability,and easy functionalization,However,coordination polymers（CPs）based on rigid pyridinecarboxylic acid ligand still presented some problems such as directional synthesis difficulty,functionalization uncertainty and incomplete exploration of potential properties.In this paper,19 coordination polymers were synthesized via self-assembly of five rigid pyridinecarboxylic acid ligands as well as transition metal and/or lanthanide metal ions.The coordination polymers were characterized by single-crystal X-ray diffraction,powder diffraction,infrared spectroscopy,and thermogravimetry analysis.Their potential applications in fluorescence sensing,proton conduction,and magnetism were explored.The relationship between synthesis conditions and structure was studied.The main contents of this paper are as follows:1.Using bicyclic rigid ligand H₃pab,six novel coordination polymers were constructed under hydrothermal conditions by introducing different metal ions.CPs 1-4 are isomoprphic lanthanide-based coordination polymers,they have three-dimensional structure with a 1D channel.Based on the characteristics of structure of organic ligands and complexes,the properties of luminescence and proton conduction of CPs 1-4 were investigated.CPs 1 and 2 can sensitively recognize the change of temperature in a certain temperature range.CPs 1-4 have good proton conductivity.The proton conductivity of 4 can reach 2.5×10^-4 Scm^-1 at 60℃and 98%RH.Considering the excellent performance of CPs 1-4,we further explored the application of transition metal centered CPs 5 and 6 in luminescence and proton conduction.The results show that CPs 5 and 6 also have proton conductivity,which is 5.24×10^-6Scm^-1and 1.54×10^-6Scm^-1,respectively.Besides,CP 5 has good solid-state fluorescence properties.This is the first time that the bicyclic rigid pyridine carboxylic acid ligand.has been used to construct the photoelectric bifunctional material.2.We have successfully synthesized CP 7,which was constructed under hydrothermal conditions via the V-shaped rigid linker H₂pdda and Zn²⁺ion.CP 7 is a one-dimensional chain structure.CP 7 can detect trace Fe³⁺,Al³⁺,Cr₂O₇^2-,nitrofurantoin,and nitrofuran by fluorescence quenching in aqueous solution.All recognition processes have good quenching constant and linear relationship.It is worth mentioning that the colour of the solution changes from dark purple to bright blue in the recognition process for Al³⁺ions.This is the first example of one dimensional multi-functional material with high efficiently and sensitivity detection ability of Fe³⁺,Cr₂O₇^2-,Al³⁺,nitrofurantoin,and nitrofuran.3.The ligand of Hpab containing pyrazole functional groups was selected to prepare coordination polymers via self-assembly method.Three 2D isostructural CPs8-10 were prepared.After exploring the luminescence and magnetism properties,we found that CP 8 can selectively recognize Cr₂O₇^2-,Cr O₄^2-and Fe³⁺ions by fluorescence quenching in aqueous solution.CPs 9 and 10 are a dominant interaction of antiferromagnetic nature.4.Based on the mixed ligand strategy,five novel coordination polymers were hydrothermally synthesized using bicyclic rigid ligand H₃cta,along with anxiliary ligands of phen and 4,4’-bipy.CP 11 has 3-connected hcb topolopical structure,CPs 12,14 and 15 are discrete monomeric structure,while CP 13 has a one dimensional chain structure with two coordination modes of Zn²⁺ions.Magnetic studies show that CPs 11and 12 have a dominant interaction of antiferromagnetic nature.Through our study,we find that during the self-assembly process of the coordination polymers,the structures of coordination polymers are regulated by ancillary ligands,reaction temperature,p H values and different metal ions.Besides,what is more important is that the ancillary ligands play significant roles in structural diversity.5.Under hydrothermal conditions,four novel coordination polymers were synthesized by reactions of H₃cpsa,phen,and transition metal ions.CPs 16 and 17 are three-dimensional structure,while CPs 18 and 19 have discrete monomeric structure.CPs 16-19 were analysized by single-crystal X-ray diffraction analysis and Hirshfeld surface.Luminescence studies show that CP 16 exhibits the strong fluorescence emission.It is noteworthy that the four coordination polymers with different structures were obtained under similar the synthetic methods and reaction solvent,while,the difference are the p H values and temperature of synthesis.This study provided an experimental basis for the later construction of complexes with diverse structure of bicyclic rigid ligand.