Synthesis And Properties Of Coordination Polymers Based On Semi-rigid Pyridine Polycarboxylic Acid Ligands

Semi-rigid pyridine polycarboxylic acid ligands have the characteristics of diverse coordination modes of carboxylic acid ligands and strong coordination ability.The introduction of pyridine groups can also bring more possibilities for the coordination mode of ligands.In addition,its structure has a certain degree of flexibility,which makes the coordination mode of ligands more flexible,and it is easier to obtain high-dimensional coordination polymers with novel structures.More and more researchers begin to use it to construct coordination polymers(CPs)with unique structures and potential applications.This paper uses two semi-rigid pyridine polycarboxylic acid ligands:5-(5-carboxy-pyridin-3-yloxy)-isophthalic acid(H₃L1)and 5-(5-carboxy-pyridin-3-yloxy)-isophthalic Acid(H₃L2)was assembled with different metal ions,and 7 new coordination polymers were obtained.In this paper,these coordination polymers were characterized by single crystal diffraction,powder diffraction,infrared and thermogravimetry.And according to the structural characteristics of each complex,their proton conduction,fluorescence,magnetic properties have been studied.These works have important significance for further research on the correlation between the structure and properties of CPs.The research content of this paper is mainly divided into the following three parts:1.Using ligand H₃L1 and transition metal ions Co(?)and Ni(?)to assemble two new heteronuclear and isomorphous CPs,{[Co₂(H₂O)₂(L)(OH)]·2.5H₂O·0.5DMF}_n(1)(DMF=N,N-dimethylformamide)and{[Ni₂(H₂O)₂(L)(OH)]·1.75H₂O}_n(2).They have a3D(4,8)-connected flu/fluorite topology,which is formed by the interconnection of tetranuclear butterfly{M₄(COO)₆(OH)₂}clusters and ligands.The structures of these two compounds are similar,but they exhibit different magnetic properties.1 shows antiferromagnetic interaction in the high temperature region,and 2 shows weak ferromagnetic interaction in the entire temperature region.The hydroxyl groups and water molecules in the skeleton contribute to the construction of the hydrogen bond network,so we tested their proton conductivity.At 363 K and 98%relative humidity(RH),the best proton conductivity of 1 and 2 are 9.07×10^-5 S·cm^-1 and 1.29×10^-4 S·cm^-1,respectively.In addition,Hirshfeld surface analysis and PLATON calculations were used to compare their hydrogen bond interaction.2.Two new CPs,[Cd(HL2)]_n(3)?[Zn_1.5(L2)(H₂O)]_n(4)were successfully synthesized under solvothermal conditions by using H₃L2 and d¹⁰ transition metal ions Cd(?)and Zn(?).In the structure of 3,the Cd(II)ion and the ligand are connected to each other to form a helical chain,and this chain is further connected via the ligand to form a3D network.4 is a 2D plane formed by the trinuclear Zn(II)cluster and six adjacent ligands connected to each other.Considering that there are incompletely coordinated carboxylic acid groups in both 3 and 4,their proton conductivity and conduction mechanism were explored.Because there are water molecules in the structure of 4,4shows more excellent proton conductivity.The best proton conductivity(?)of 3 and 4 at363K and 98%RH are 6.60×10^-5 S·cm^-1 and 1.30×10^-4 S·cm^-1,respectively.3.Under hydrothermal conditions,H₃L1 and rare earth metal ions are used as raw materials to self-assemble a series of CPs with photoelectric dual functions,[Ln(L)(H₂O)]_n(Ln=Ce(5),Tb(6),Eu(7)).Their structure is a 3D framework by connecting the paddle-shaped dual-nuclear Ln(?)clusters with adjacent ligands.According to the different characteristics of different metal centers,their properties in proton conduction and fluorescence sensing are explored.The best proton conductivity(?)of 5 at 363 K and 98%RH is 2.98×10^-5 S·cm^-1.In addition,6 and 7 both have good light-emitting properties.CP 6 is an excellent fluorescence sensor for detecting anions and cations.It can identify Fe³⁺,Cr O₄^2-,Cr₂O₇^2-ions efficiently and selectively.