Synthesis Of Cuprous Iodide Complexes Of S-containing Bipyridine And Its Reduction Of Carbon Dioxide

Recently,a lot of researches have been made on transition metal complexes with d¹⁰electronic configuration with good light-emitting properties.Cu(I)complexes have attracted widespread attention as a new luminescent material,which replace noble metal complexes due to its rich content and easy accessibility.Studies have shown that Cu(I)complexes have excellent light-emitting properties.Besides,researchers found that Cu(I)complexes can be used to reduce and fix the greenhouse gas CO₂ in recent years.Therefore the synthesis of complexes with specific functions has become a hot research topic in recent years.In this paper,three different bipyridine ligands bearing S-containing groups,5,5'-bis((p-tolylthio)methyl)-2,2'-bipyridine(L1),5,5'-bis((benzylthio)methyl)-2,2'-bipyridine(L2)and 6,6'-bis((p-tolylthio)methyl)-2,2'-bipyridine(L3)were synthesized to react with CuI.Three new coordination polymers were successfully synthesized:Cu₂I₂(L1)(1),Cu₁₂I₁₂(L2)₄·(H₂O)₄(2),Cu₂I₂(L3)(3).Complexes 1 and 2 have a one-dimensional chain structure,and complex 3 has a four-core zero-dimensional structure.X-ray single crystal diffraction indicates that complexes 1 and 3 have a Cu₄I₄ step-cubane core.In 1,one Cu(I)ion is coordinated with two nitrogen atoms in the ligand molecule and two iodine ions,the other Cu(I)ion is coordinated with three iodine ions and sulfur atom in the ligand.Four Cu(I)ions are bridged by iodine anions to form a step-cubane Cu₄I₄ unit,and these units are further connected to generate a one-dimensional chain structure through Cu-S interaction.In the asymmetric unit of complex 2,four ligand L2 molecules can be divided into two groups,where two ligands in one group are connected by two Cu₂I₃ units through Cu-S interaction and Cu₂(?-H₂O)₂ via Cu-N bonds to form a quadrangle.However two quadrangles are parallel but arranged perpendicularly,and two Cu₂(?-H₂O)₂ groups in two quadrangles are connected through weak Cu-O interaction to form a closed cubic alkane core.Finally these large asymmetric units are connected by step-cubane Cu₄I₄ cluster cores to generate a one-dimensional coordination polymer.Interestingly,2 has high activity and can reduce carbon dioxide to oxalate to form the oxalate-bridged dimmer,Cu₂I₂(L2)₂(?-C₂O₄)(4).In 4,two mononuclear Cu(II)coordination units are linked by oxalate in a bridging manner to form a dinuclear complex.Because 1 and3 do not have this property,it is presumed that the Cu₄(H₂O)₄ core unit of complex 2 with water molecules may play a role in reducing carbon dioxide.The luminescence properties of these complexes were discussed preliminarily,and their solid emission spectra were studied.The analysis of the emission spectra showed that complexes 1 and 3 display low energy emission bands.The emission band of 1 is at 616 nm and the band of 3 is at 626 nm.These emissions originate from the excited state of the Cu₄I₄cluster in CuI complex.However the emission band of 2 is not observed,which may be caused by emission quenching due to water molecules participating in coordination.