Theoretical Study On Ligand Stabilization Mechanism And Properties Regulation Of Silver Nanoclusters

Silver nanoclusters（Ag NCs）are important nanomaterials with promising applications and have attracted a lot of research attention in sensing and catalysis due to their unique electronic and optical properties and catalytic performance.In recent years,ligand-protected Ag NCs have attracted a large number of studies from various chemistry-related fields.A large number of experiments have shown that the structure of Ag NCs is affected by the size and type of ligands that stabilize the structure,therefore,it is important to explore the ligand-regulated effects of the nanocluster geometry.Improving stability and functionality is a top priority in the study of silver nanoclusters,and the incorporation of heterometallic atoms in monometallic nuclei has been shown to be an effective strategy for obtaining stable and functional silver nanoclusters.In this paper,a theoretical study of the structure and related properties of two typical Ag NCs based on density functional theory is carried out,and the research work includes the following two parts.The first part:Density functional theory was used to investigate the ligand effects of geometric and electronic structure for face-centered cubic（FCC）Ag₁₄（SR）₁₂（PR’₃）₈（R/R’=H,CH₃,Ph）nanoclusters and Ag₁₄S（SR）₁₂（PR’₃）₈（R/R’=H,CH₃,Ph）silver sulfide molecular nanoclusters.They are similar cube-like structures,and their geometrical structures show obvious SR-related ligand effects.That is the shell structure is compressed by SH ligand and deformed by SCH₃ligands,while regular bulk structures can be obtained in the presence of SPh ligands.The regular and compressed structures maintain a high degree of T_hsymmetry,in contrast,the symmetry of the cluster was reduced to C₁symmetry after replacing the ligand with SCH₃,and the optimized structure was deformed,which is the first time that the ligand deforms the structure by reducing the symmetry of the cluster observed in silver clusters.Further,the Atoms in Molecules（AIM）theory reveals that ligand changes the strength of the bond by affecting the electron density distribution of Ag-S bond in the shell layer,and then the structure is changed.The electron density distribution condition to maintain the stability of the structure is that the difference of the electron density distribution of the Ag-S bond in the shell layer is less than 0.001au.On this basis,the ligand modulation effect on the electronic structure properties of the above clusters is calculated.The second part:The modulation of the structure and properties of body centered cubic（BCC）silver nanoclusters by single-atom doping was systematically investigated by DFT.The[Ag₁₄（C≡C-^tBu）₁₂]²⁺and[Ag₁₅（C≡C-^tBu）₁₂]⁺nanoclusters have exactly the same silver atoms stacking pattern as well as ligand linkage.Theoretical calculations show that single-atom doping enhances the thermodynamic stability of the nanoclusters and exhibits a significant modulation effect on the cluster properties.The doping generally leads to enhanced thermodynamic stability of the NCs and exhibits significant modulation of the nanocluster properties.Among them,the compactness of the clusters structure after doping with nonmetallic atoms X（X=F,Cl,Br,S,Se,Te）gradually decreases in the order of top-down electronegativity of heteroatoms within the same main group,and the nature of the electronic structure is obviously changed,and the Ultraviolet-visible（UV-vis）absorption spectra show a general red shift in the position of the absorption peaks.For the heterometallic M（M=Cu,Au,Ni,Pd,Pt,Zn,Cd,Hg）atoms,except Cu atom,which tends to occupy shell layer sites,the others prefer substitution at kernel positions.The differences in HOMO-LUMO gaps and UV-vis absorption spectrum of MAg₁₄nanoclusters after atoms doping indicate the importance of the heteroatoms in modulating the electronic structure properties of the silver nanoclusters.The differences in the electronic structure of the clusters are obtained from the alteration of the heteroatom contribution to the front-line orbital elements and the effect on the charge transfer mode between the fragments during the S₀→S₁leap by Kohn-Sham energy level analysis,hole-electron analysis and interfragment charge transfer analysis.