Research On Co-protected Ag₅₀ Nanocluster And Its Doping

Noble metal nanoclusters(diameter<2 nm)have attracted great attention for their unique properties which are different from macroscopical stuff.In this ultrasmall size range,nanoclusters lose the plasmonic features and show molecular properties.Determination of nanocluster structure provides the possibility to study their related properties,especially the larger ones which have great potential application in many fields.In recent years,a large number of gold nanoclusters have been synthesized and their crystal structures has been identified as well,including Auis,Au20,Au21,Au22,AU23,AU24,AU25,AU30,AU36,AU37,AU38,AU40,AU44,AU52,AU92,AU92,Au102,Au130 and Au133,etc.With the analysis of the structure,the relationship between properties and structure can be known and summarized,so that they can be applied in many aspects,such as energy conversion,catalysis,photochemistry,biological application and magnetism,etc.Silver,as the kindred of gold,has gradually attracted people's attention due to its rich reserves,cheap price,convenience to obtain,and stable physico-chemical properties.The silver nanoclusters are getting more and more attention since the crystal of the first thiolated silver nanocluster Ag44 was reported in 2013.However,the silver nanoclusters that have been reported in several years are still very few,only Ag14,Ag16,Ag25,Ag29,Ag32,Ag44 and so on.How to synthesize silver nanoclusters,especially large silver nanoclusters is still a problem.Based on a great deal of previous work and resources in our lab,the research,utilizing Ag44 as the raw material,synthesizes a silver nanocluster which is protected by double ligand and have more atom by "seed growth method".Then,a certain amount of gold atoms are doped to the silver nanoclusters by the "metal exchange method" to synthesize the alloy nanoclusters.The thermal stability and the fluorescent properties of alloy nanoclusters are better than the Ag nanoclusters.The main content is as follows:Synthesizing co-protected Agso nanoclusters by the“seed growth method".Firstly utilizing p-mercaptobenzoic acid(p-MBA)as the ligand to prepare Ag44(p-MBA)30 nanoclusters.Then utilizing Ag44 as raw materials("seeds")to react with the ligands bis(diphenylphosphino)methane and 4-tert-butylbenzyl mercaptan.Through these characterization methods,such as X-ray photoelectron spectroscopy(XPS),electrospray mass spectrometry(ESI-MS),and X-ray single crystal diffraction it can be proved that the target production is an overall composition of Ag50(Dppm)6(SR)30 co-protected by bis(diphenylphosphino)methane and 4-tert-butylbenzyl mercaptan.The new clusters retain the core structure of Ag44-a double dodecahedron consists of 32 metal atoms,and have two symmetrical Ag9(SR)15P6 ring motifs.The new clusters have 20 valence electrons,which can be attributed to globose colloidal model.This work not only reports a new larger size nanoclusters but also provides a new way to synthesize larger size silver,that is,"seed growth method".Synthesizing the AuxAg50-x nanoclusters protected by double ligand through metal exchange method.The AuxAg50-x nanoclusters are synthesized from the reaction of Ag50 nanoclusters and sulfur gold.Alloy nanoclusters have similar optical properties with silver nanoclusters,but it has significantly improved in thermal stability and fluorescence.AuxAg50-x nanoclusters are characterized by X-ray single crystal diffraction,mass spectrometry,X-ray photoelectron spectroscopy,UV-Vis absorption spectra,and thermogravimetric analysis.Structural analysis shows that the doping sites of gold atomthe of AuxAg50-x nanoclusters is on the M12 core,the innermost layer,and the peripheral protective groups are unchanged.The DFT calculation also confirms that gold atoms are doped on the M12 kernel on average.Furthermore,through the comparison of the properties of the Agso nanoclusters and AuxAg50-x nanoclusters,it can be found that the thermal stability and fluorescence of the alloy nanoclusters have improved.Electrochemical experiment proves that the gold atoms not only affectes the LUMO orbital of the clusters,but also can change the HOMO orbital for the first time,which can improve the stability of alloy nanoclusters.This work on the one hand provides a case study for the relationship between properties and element composition,on the other hand proves the application value of"metal exchange method" in the synthesis of silver-based alloy nanoclusters.