Synthesis,Structure And Properties Of Copper Clusters Protected By Mercaptoimidazole Ligands

Atomically precise coinage metal(Au,Ag,Cu)nanoclusters have diverse structures and excellent optical properties.As a new type of luminescent materials,they have broad prospects in the applications of fluorescence sensing,biomedicine,and light-emitting devices.The relatively plentiful and cheap copper endows copper clusters unique advantages in practical applications than gold and silver.Meanwhile,due to the unique optical properties and electrochemical activity,Cu nanoclusters are favored by scientific researchers.However,atomically precise Cu(I)nanoclusters protected by thiolate ligands is rarely reported due to the sensitivity of Cu(I)in air.In order to overcome this obstacle,a mercaptoimidazole ligand with two coordination sites have been chosen for the construction of stable Cu(I)clusters.The N heteroatom in the ligand might also enrich the charge transfer paths,which is useful for improving their luminesce performance.Meanwhile,we have selectively added phosphine auxiliary ligands during the synthesis to further improve the stability of the structure.Overall,our work is divided into the following two parts:Firstly,we have successfully prepared a novel mercaptoimidazole-stabilized copper(?)duster:[Cu13(C7H5N2S)12]NO3(1)by introducing the reducing agent(NaBH4),and its composition has been successfully elucidated by X-ray crystallography and electrospray ionization mass spectrometry(ESI-MS).The metal framework of 1 can be seen as three triangular bipyramids sharing one or two vertices,which is surrounded by 12 thiolate ligands as protecting units through a simple bridging motif.Compound 1 exhibits well stability under ambient conditions and shows a bright-red emission in the solid state(Em=627 nm).The quantum yield of the solid-state sample was calculated to be 1.36%.Compound 1 has a long-life emission of phosphorescence in the order of microseconds and a large stokes shift(?280 nm).Meanwhile,two exposed copper atoms at the ends of the metal framework endow the clusters a good electrochemical activity in electrochemical detection of H2O2.This work provides a platform to investigate the structure-optical and electrochemical property relationship of copper clusters.Secondly,a series of copper(?)clusters:Cu6(C7H5N2S)6(2),Cu4I(PPh3)3(C7H5N2S)3·THF·CH3CN(3)and[Cu8I(PPh3)3(C7H5N2S)6]+(4)have been synthesized by using 2-mercaptobenzimidazole,triphenylphosphine and CuI.Their single crystal structures were successfully analyzed by X-ray single crystal diffraction technique.The X-ray powder diffraction patterns verified their phase purity.Meanwhile,collective luminescence characterizations of compounds 3 and 4 were carried out considering their intense blue light and orange light emission under 365 nm UV irradiation.The emission spectra show that the maxum emission of compound 3 and compound 4 are at 458 nm and 598 nm,respectively.The quantum yield of compounds 3 and 4 were measured to be 20.19%and 21.51%,respectively,by a four-step integration method.These sub-nano clusters are expected to become new nanomaterials in the LED field.This work provides a reference for the preparation of stable Cu(I)clusters with high emission efficiency.Of note,compound 3 can transform into compound 4 in methanol solvent,which was verified by ESI-MS and fluorescence experiments.