Synthesis And Properties Of Cuprous Coordination Polymers Based On Linear Bis(N-pyridylbenzimidazole)Ligands

With novel structures and excellent properties,cuprous coordination polymers have received widespread attention for their applications in catalysis,luminescence,adsorption and so on.At present,the structure activity relationship of cuprous coordination polymers has not been studied in depth,especially in the field of electrochemical catalysis.Cuprous ions in the electron configuration of d¹⁰ have variable valence states,easily adjustable coordination modes and skeletal structures,which are catalysts commonly used in industrial production and scientific research.In this work,linear bis（N-pyridylbenzimidazole）ligands were designed,cuprous coordination polymers were synthesized by solvent diffusion and solvothermal methods,electrochemical and fluorescent properties of these polymers were investigated,the structure activity relationships were explored,which laid the foundation for the expansion of the research field of cuprous coordination polymers.Details of the work are as follows:（1）Synthesis and structural characterization of cuprous coordination polymersTwo new linear bis（N-pyridylbenzimidazole）ligands,2,2’-（1,3-propanediyl）-6,6’-bis（3-methylpyridine）bis-1,3-benzimidazole（L¹）and2,2’-（1,4-butanediyl）-7,7’-bis（3-methylpyridine）bis-1,4-benzimidazole（L²）,were designed and reacted with cuprous salts,and nine structurally novel cuprous coordination polymers were synthesized by applying solvent diffusion and solvothermal methods,with the following molecular formulae:{[Cu（L¹）]X·y CH2Cl2}n（1,X=BF4,y=2;2,X=Cl O4,y=2;3,X=PF6,y=1）{[Cu（L²）（CH3CN）]X}n（4,X=BF4;5,X=Cl O4）{[Cu2（L²）1.5（PPh3）]（X）2}n（6,X=Cl O4;7,X=PF6）{[Cu₂（L¹）（μ₂-I）₂]·DMF}_n（8）{[Cu（L²）_0.5（μ₂-I）]·DMF}_n（9）Structural analysis shows that 1–5 as well as 8–9 are one-dimensional chain structures and6–7 are two-dimensional layered structures.The central ion adopts a tetra-coordinated twisted tetrahedral geometry in the one-dimensional cuprous coordination polymer,and both a three-coordinated planar triangular structure and a tetra-coordinated twisted tetrahedral geometry in the two-dimensional cuprous coordination polymer.The ligand L¹ exhibits aμ₃-（κ_N¹,κ_N¹,κ_N¹,κ_N¹）coordination mode in the coordination polymer,and L² exhibitsμ₄-（κ_N¹,κ_N¹,κ_N¹,κ_N¹）andμ₂-（κ_N¹,κ_N¹）coordination modes.（2）Electrocatalytic dehydrogenation of cuprous coordination polymer modified electrodesThe synthesized cuprous coordination polymers and acetylene black were grinded thoroughly and added to Nafion solution for ultrasonic vibration,and then coated on the surface of glassy carbon electrode（GCE）to obtain cuprous coordination polymer/acetylene black/Nafion modified glassy carbon electrodes（CP 1–9/GCE）.The electrode without complex modification was blank electrode（bare/GCE）.The electrocatalytic dehydrogenation performance of the electrodes modified with the cuprous coordination polymers was determined by cyclic voltammetry（CV）,linear scanning voltammetry（LSV）,and electrochemical impedance spectroscopy（EIS）experiments.The results showed that the cuprous coordination polymers 6 and 7 had no electrocatalytic dehydrogenation activity;other cuprous coordination polymers showed a positive shift of 74～263 m V in overpotentialη10（298 K）and Tafel slope in the range of 103～173 m V dec^-1 compared to the blank electrode.The above data indicate that the seven cuprous coordination polymers exhibit fine electrocatalytic hydrogen precipitation performance in the order of activity:1>2>4>3>5>8>9.Further analysis of structure-activity relationship found the following conclusions:i.The more stable the cuprous coordination polymers are,the lower the electrocatalytic dehydrogenation activity is;Cuprous ion is a soft acid,which can form more stable soft pro-soft coordination polymers with soft bases（triphenylphosphine,iodine ions）,and is not easily deformed to obtain active intermediates,resulting in low or even no activity of electrocatalytic dehydrogenation activity.ii.The difference in catalytic activity of isomorphic cuprous coordination polymer 1–3 depends on the deformability of forming the chelating eight-component ring.The greater the deformability,the easier the formation of active intermediates,and the higher the electrocatalytic dehydrogenation activity.（3）Electrochemical sensing of cuprous coordination polymer modified electrodesThe performance of CP 1–9/GCE in identifying glucose was investigated by chronoamperometry（CA）.The results showed that CP 1–9/GCE could achieve quantitative detection of glucose solution in the range of 1μM～4 m M with the sensitivity of 6.277～22.375μA/m M and the theoretical limit of detection（LOD）of 0.029～0.154μM,among which the highest sensitivity was achieved by CP 1/GCE,and the CP 1–9/GCE electrochemical sensors showed excellent stability and interference immunity.（4）Solid-state fluorescence properties of cuprous coordination polymersThe solid-state fluorescence properties of the cuprous coordination polymers 1–9 were investigated.Compared with the ligands,the solid fluorescence peaks of 1–9 underwent a significant red shift of more than 100 nm,which was attributed to the metal-ligand charge transfer（MLCT）;the fluorescence intensities of 1–3 and 8–9 were enhanced and 4–7 were partially quenched,which were associated with the type of ligands—the coordination of triphenylphosphine caused a decrease in the amplitude of the red shift of the fluorescence peak and a partial quenching of the fluorescence;the coordination of the pure nitrogen ligands led to an increase in the amplitude of the red shift of the fluorescence peak and an increase in the fluorescence intensity.In conclusion,in this work,nine structurally novel cuprous coordination polymers were synthesized through ligand design,anion and synthesis method selection,and glassy carbon electrodes modified with cuprous coordination polymers/acetylene black/Nafion were prepared to study the electrocatalytic dehydrogenation and electrochemical sensing,and the solid-state fluorescence properties of the coordination polymers were investigated.The results show that the cuprous coordination polymers can be used as bifunctional catalysts for electrocatalytic dehydrogenation and electrochemical sensing of glucose,the properties of which can be regulated by the structure;the solid-state fluorescence properties show that the fluorescence of the cuprous coordination polymers can be regulated by the use of different types of ligands.