Construction And Photo-electric Properties Of Coordination Polymer Based On 2-mercaptoisonicotinic Acid

People have deeply realized the important guiding role of sulfur in the field of coordination chemistry,so the academic community has carried out extensive exploration on the theoretical research and practical application of metal-organic compounds constructed with sulfur as organic ligand.Among them,sulfhydryl nitrogen heterocyclic ligands provide a variety of coordination centers and coordination modes for the design and synthesis of new complexes due to the inclusion of-N=C-SH（?）-NH-C=S interconvert functional groups including S atoms and N atoms.In view of the great influence of organic fragments on the construction process of the complexes they guide,and different from the common idea of building complexes with large conjugated systems of carboxylic acids.In this paper,2-mercaptoisonicotinic acid（H₂L）was selected as the linker.Five new coordination compounds were constructed in different solvent systems by solvothermal strategy,and their structures and properties were explored by various testing methods.The main contents are as follows:1.With theⅧgroup elements Co and Ni as the metal centers,in the mixed system of acetonitrile and water,using ethylenediamine（en）as the p H regulator,two kinds of pentaconuclear cluster coordination polymers with the same spatial configuration were synthesized by regulating the degree of deprotonation of H₂L:{[Co₂（L）₄]·4H₂O}_n（1）、{[Ni₂（L）₄]·4H₂O}_n（2）.Complexes 1-2 exhibit attractive three-dimensional network structure through intermolecular forces such as hydrogen bonding,π...πstacking.The magnetic properties of 1-2 varying with temperature are briefly discussed.The results show that both of them have antiferromagnetic interaction.In addition,the electrochemical performance of 1-2was further tested considering the broad prospect of the complex material with Co/Ni as the node in the field of supercapacitors.A three-electrode system was built in KOH（1 M）electrolyte,and the effects of metal salt types and load on electrode capacitance were investigated.The results showed that electrode material 2 showed better electronic transmission and storage capacity(0.5 A g^–1:745 F g^–1)and ideal cycle stability(3000 cycles,1 A g^–1:86.9%)than 1,which greatly enriched the design scheme of Co/Ni-based coordination compounds in the electrochemical industry.2.Using transition elements Pb,Zn,Cd as metal nodes,and H₂L in methanol-acetonitrile mixed system,three complexes with specific fluorescence properties were synthesized:{[Pb LO₂]·2H₂O}_n（3）、{[Cu₃L₆（en）]·3H₂O}_n（4）、{[Cu₆Cd₃（L）₆（en）]·3H₂O}_n（5）.The sulfhydryl fragment of complex 3 is cleverly oxidized to-SO₂.4-5 forms a metal-organic framework with typical Cu₆S₆stable structure due to the introduction of Cu（I）source.The formation of Cu₆S₆cluster takes full advantage of the good binding ability between S and another metal Cu,and the topological network with three-dimensional porous structure is obtained after connecting with d¹⁰transition metal.Under UV irradiation,solid complex 3showed obvious yellow light emission,while complex 4-5 showed bright red light.The fluorescence sensing effect of 4-5 on a series of nitro compounds（nitrobenzene,2-nitrotoluene,4-nitrotoluene,2-nitrophenol,4-nitrophenol）in pure water environment was further recorded.The higher quenching constant and lower detection limit showed that 4-5could serve as a fluorescence probe for the recognition and detection of nitro compounds in water samples,which is of great significance for the monitoring of water quality safety.The detailed fluorescence quenching mechanism is proposed,which provides strong support for the experimental data.