Theoretical Study On Isomerization Mechanism Of Gold Nanoclusters Protected By Thiol Ligand

Gold nanoclusters have unique physical and chemical properties.Gold nanoclusters had attracted wide attention from researchers due to their huge application potential in the fields of medicine,luminescence,catalysis,nanoelectronics,etc..The isomerization phenomenon and controllable temperature conditions of gold nanoclusters protected by thiol ligands to convert between the two isomers have always been one of the research hotspots in the field of gold clusters.In this paper,the possible isomerization mechanism of gold nanocluster isomers and a series of chiral enantiomers was studied in detail through the density functional theory(DFT)calculation method.The research content was mainly divided into the following two parts.Part 1:The isomerization mechanism of Au₂₈(SR)₂₀ cluster isomers that have been reported in two types of experiments was studied by DFT.Based on the ligand exchange mechanism,two possible paths for the isomerization of Au₂₈(SR)₂₀ isomers were proposed.Both of these two routes use HSCH₃ as the introduction group,through the S in HSCH3 nucleophilic attack on the Au atoms of the gold cluster ligand layer,thereby opening the Au-S bond and inducing the Au-S at positions 3and 4 of the third-level"staple"of Au₂₈(SR)₂₀-iso1 cluster fractured.Then two the third-level"staples"and first-level"staples"in the ligand layer were broken and recombined to form four the second-level"staples".The transition from Au₂₈(SR)₂₀-iso1 to Au₂₈(SR)₂₀-iso2 was realized.In addition,based on the theory of molecular dynamics,a new method of Au-S bond breaking was discussed,that is,the collision of between molecules breaked the chemical bond,and a new understanding of Au-S fracture is proposed from a theoretical perspective.Part 2:The chiral reversal mechanism of Au₂₂(SR)₁₈,Au₂₈(SR)₂₀,Au₃₄(SR)₂₂ and Au₄₀(SR)₂₄ clusters of homologous structures was studied.The racemization mechanism of a series of gold clusters of fcc configuration was explored by the method of restrained structure delay.The two relatively staggered and parallel Au triangles of the core Au7 unit rotated in opposite directions at the same time,and drived the connected"staples"whirled,which causes the other Au atoms in the inner core to slide relative to each other.Finally,the ligand layer also took place orientation reversal and realized the chirality reversal of the entire cluster.The fracture and formation of Au-S did not occur during the above process,and the energy barrier of this process was also in good agreement with the experimental results.At the end of this part,we summarized the configuration rules of clusters that can undergo epimization.This paper explored the isomerization and chirality reversal mechanism of gold nanoclusters through theoretical calculations,which is helpful to understand the mutual transformation between cluster isomers at the atomic level and provided theoretical guidance for the design of special properties nanoclusters.