Theoretical Studies On The Au-S Skeleton Isomerism And Cluster Structure Of Thiolate-protected Gold Nanoclusters

Exploring the structure of clusters and then summarizing the structural regulation of clusters and the relationship of structure-property is one of the most important and basic scientific issues in the research field of nanoclusters.To date,the thiolate-protected gold nanoclusters is one of the most widely studied system in nanotechnology,due to their great potential for applications in the fields of catalysis,sensing,fluorescence labeling,biomedicine,etc.This paper focuses on these structures of Au28(SR)20,Au22(SR)16 and Au15(SR)13 clusters.These possible structures of three clusters were systematically studied through theoretical calculations.Moreover we theoretically studied some stable isomers by calculation.These structures provide a new theoretical perspective for understanding the evolution pathway of structure and structure-property relationship of thiolate-protected gold clusters.The main research content of this paper includes the following two sections:(1)We theoretically predicted the third isomer structure of the Au28(SR)20 cluster.The Au28(SR)20 cluster was thought to be a key cluster intermediate in view of the structural evolution of fcc-structured thiolate-protected gold clusters.Two stable Au28(SR)20 clusters were reported experimentally,from this two types of Au-S skeleton evolution pathways have been derived.Based on theoretical analysis,we theoretically predicted the third isomer structure of the Au28(SR)2O cluster.The new Au28(SR)20 isomer was also suggested to be the key link in the evolution of Au-S framework from Au22(SR)8 to Au34(SR)22 and then to Au40(SR)24 clusters,which had the same Au14 gold core but quite different ligand shells in comparison to two experimentally reported Au28(SR)20 clusters.Geometric optimizations of the new isomer structure carried out by DFT calculations,and the thermodynamic stability of the cluster was investigated.We found that the energy of the new isomer was close to that of two known clusters.The stability of the new isomer was further verified by investigating the ligand effect.On basis of these three clusters evolution pathways,a common gold core and staple motif growth pattern was suggested and two new isomer structures of Au36(SR)24 and Au44(SR)28 were obtained.(2)Structures prediction of Au22(SR)16 and Au15(SR)13 clusters.Based on theoretical study,we searched for different structures of gold-core and obtained nearly 50 Au22(SR)16 isomers.The energy and optical properties of these Au22 isomers were studied by theoretical methods,and a new insight into the structure of Au22(SR)16 cluster was presented.At present,Au15(SR)13 is a relative stable thiolated gold nanocluster experimentally identified.Although early theoretical work performed predictions on this structure,its structure has not been accurately resolved.Based on the rapid development of this field and the new understanding of the structure of thiolate-protected gold clusters,we predicted a new isomer of Au15(SR)13,which had a Au4 gold-core,two dimeric motifs and a[Au7(SR)7]unit.