Synthesis,Characterization And Doping Mechanism Of Ag-Cu Alloy Nanoclusters

Atomic nanoclusters are atomically accurate and have attracted wide attention due to their unique optical,electronic,dielectric,magnetic and chemical properties.By adjusting the combination of two or more metals in the nanoclusters(NCs),some properties can be changed,which usually leads to the enhancement of the required properties,such as the luminescence performance,catalytic performance,etc.In recent years,more and more researchers have carried out in-depth research on the alloying of metal nanoclusters.As for coin metals,the alloying of Au and Ag have been studied deeply,followed by the alloying of Au and Cu,but the study on the alloying of Ag and Cu is very little.In this paper,we use one-pot co-reduction method and metal exchange method,Ag44 and Cu25 as templates,respectively,using MS,UV-Vis,SC-XRD and XPS,to study the heteroatom doping number and doping sites of(CuAg)44 and(AgCu)25H10 alloy nanoclusters.Inter-cluster reaction method was used to study the inter-cluster reaction of Ag44 and Cu25.The main contents of this paper are summarized as follows:First,(CuAg)44 alloy nanoclusters were studied using[Ag44(SC6H3F2)30]4-as templates.(1)The(CuAg)44(ie[CuxAg44-x(SC6H3F2)30]4-)alloy nanoclusters were synthesized by one-pot co-reduction method.The number of heteroatomic Cu doped in the clusters was related to the molar ratio of Ag/Cu.According to the MS data,the doping degree could be continuously adjusted from 0 to 12,indicating a high doping degree.It is found that the number of doped Cu is positively correlated with the mole fraction of Cu in the feed.But with the addition of Cu heteroatom,a new product[Cu12Ag28(SC6H3F2)24]4-will be formed.SC-XRD clear evidence that the doped Cu atoms in(CuAg)44 occupy the exterior motif.At the same time,UV-Vis and XPS were performed to further confirm the authenticity of the alloying and the doping sites on the exterior motif.The temperature effect and solvent effect are also studied.(2)The(CuAg)44 alloy nanoclusters were synthesized by metal exchange method,and only 2 heteroatoms could be captured by mass spectrometry,indicating a low doping degree.The doping effect of this method is far less than that of the one-pot coreduction method,which can be attributed to the high stability of[Ag44(SC6H3F2)30]4due to its closed geometry and electron shell structure,which makes it difficult for heteroatom Cu to be doped into(CuAg)44 alloy nanoclusters.Secondly,(AgCu)25H10 alloy nanoclusters were studied using[Cu25(SC6H3Cl2)18H10]3-as template.The main results are as follows:(1)The(AgCu)25H10(ie[AgxCu25-x(SC6H3Cl2)18H10]3-)alloy nanoclusters were synthesized by one-pot co-reduction method.The doping degree of heteroatom Ag is 0-4 and does not change the number of negative hydrogen.There is no direct relationship between the number of heteroatom Ag and the molar ratio of Cu/Ag,but it is more difficult to form(AgCu)25H10 alloy nanoclusters with the increase of Ag addition.And with the addition of Cu heteroatoms,a new product[Ag28Cu12(SC6H3Cl2)24]4-will be formed.SC-XRD proved that the doped Cu atoms in(AgCu)25H10 occupied the metal nuclear sites directly connected to SR ligands(that is,kernel shell doping,and exterior motif doping);UV-vis spectra confirmed the authenticity of its alloying;X-ray photoelectron spectroscopy further confirmed that the doping sites could not be located in the center of metal nuclei.(2)(AgCu)25H10 alloy nanoclusters were synthesized by metal exchange method,and only 0-4 heteroatoms were captured by mass spectrometry.It shows that in the system with[Cu25(SC6H3Cl2)18H10]3-as template,whether by one-pot method or metal exchange method,Cu is not easy to be replaced by heteroatom Ag.This may be due to the large difference in atomic radius between Cu and Ag.Thirdly,the inter-cluster reaction between[Ag44(SC6H3F2)30]4-and[Cu25(SC6H3Cl2)18H10]3-was studied.Using the method of inter-cluster reaction,the ESI MS showed that metal exchange,ligand exchange and metal-ligand fragment exchange took place,and highly doped[Ag44-mCum(SC6H3F2)30-n(SC6H3Cl2)n]4-(m=2-10,n=4-10)、[Ag44mCum(SC6H3F2)30-m(SC6H3Cl2)m(PPh4)]3-(m=3-10,n=5-10)、[Cu25mAg3+m(SC6H3Cl2)18-n(SC6H3F2)3+nH10]3-(m=0-4,n=5-12)etc.It is found that the template selection and doping of inter-cluster reaction are closely related to the feed ratio.