Synthesis And Conductivity Properties Of Metal Organic Frameworks Based On N,S-mix Donor Ligands

Metal-organic framework（MOF）is widely used in gas separation and storage because of its high inherent porosity.However,MOF usually exhibits very low electronic conductivity.For most known MOFs,the construction mode is that metal ions combine with redox inert organic ligands through"hard"oxygen or nitrogen coordination atoms,and the bonding property is mainly ionic bond.Therefore,like typical ionic crystals,the vast majority of MOFs do not provide any low-energy path for charge transmission,nor do they provide free charge carriers,which is manifested as insulators with conductivity lower than10^-10 S·cm^-1.The application of MOF is limited in the occasions where the conductivity of materials is required,such as supercapacitors,electronic transistors,batteries and electronic equipment.Compared with other materials,MOF has higher designability and adjustability of structure and properties.Therefore,it has been the goal of researchers to adopt effective design strategies to synthesize porous frameworks with good charge mobility and conductivity.In this paper,two kinds of N,S Mixed coordination MOFs:[Cu₂（DHBDI）₃（SO₄）₂]_n（MOF 1）and[Cu₂（QIDTL）]_n（MOF 3）were designed and prepared,and their conductivity,chemical stability,thermal stability,adsorption and separation properties were studied.The main research contents are as follows:Imidazole disulfide ligand:1,5-dihydrobenzo[1,2-d:4,5-d’]diimidazole-2,6-disulfide（DHBDIT）was synthesized in one step from 1,2,4,5-phenyltetramine hydrochloride.Three dimensional MOF[Cu₂（DHBDI）₃（SO₄）₂]_n（MOF 1）with good stability and high proton conductivity was synthesized by solvothermal method.MOF 1maintains good stability in boiling water,weak acid and weak base.Its structure remains stable after soaking in water,sulfuric acid solution with p H 4 and sodium hydroxide solution with p H 12 for 6 days,or boiling in boiling water for 24 hours.MOF 1 showed1.14×10^-3 S·cm^-1 at 90°C and 98%RH has high proton conductivity,and its proton conductivity increases with the increasing of temperature and humidity,which is obviously temperature and humidity dependent.Combined with the results of single crystal structure and proton conductivity,the conduction path and conduction mechanism of MOF 1 were discussed,and the adsorption properties of MOF 1 for some common gases（H₂、N₂、CH₄、CO₂、C₂H₂、C₂H₄ and C₂H₆）were studied.Then Quinoxaline-2,3-dithiol（DHQLDI）,a dithiol ligand containing N heterocycle,was synthesized from o-phenylenediamine.Then one-dimensional MOF[Cu₂（QIDTL）]_n（MOF 3）was constructed based on solvothermal method.Single crystal X-ray diffraction results show that MOF 3 is an infinite chain structure.The intrinsic electronic conductivity of MOF 3 is only 4.5×10^-9S·cm^-1,but the conductivity is significantly improved after iodine oxidation doping.Our work is of significance and potential value for expanding the type of imidazole ligands and the investigation of N,S-mix donor ligands on the modification and conductivity tuning of conductive MOFs.