Theoretical Study On Hollow Structure Of Au₁₄₄ Cluster And Carbene Ligand Stabilization Mechanism Of Ag₂₉ Cluster

Gold and silver nanoclusters(NCs)have attracted a lot of research attention in the fields of bioengineering,materials,optoelectronics and catalysis because of their unique electronic properties,optical and catalytic properties.In the past two decades,the synthetic characterization,structural elucidation and properties of ligand-protected gold and silver nanoclusters have become a research hotspot and frontier in nanochemistry,inorganic chemistry and materials chemistry.A large number of previous experimental studies have shown that changes in the size and type of cluster-stabilizing ligands often affect the structure and properties of the clusters to different degrees,so it is necessary to explore new protective ligands.In this paper,the structure and properties of two typical gold and silver nanoclusters are systematically investigated by density functional theory(DFT).The study is divided into two parts as follows.The first part:The mechanism of stable formation of unique hollow structures of thiol and alkynyl based ligand-stabilized neutral Au₁₄₄L₆₀(L=SR or C?CR)clusters was probed by using density functional theory.The first formula for calculating the average formation energy of gold-protected clusters of single species of ligands such as thiols and alkynyl ligands is proposed,and the average formation energy of 12solid/hollow clusters of close structural general formula Au_145-3N(SR)_60-2N(N=0-5)in terms of size and structure is analyzed from this perspective.Theoretical calculations show the Au₁₄₄(SR)₆₀ cluster have a significantly lower central Au atomic stability energy than the solid cluster Au₁₃₃(SR)₅₂ and Au₁₃₀(SR)₅₀,which have been reported experimentally.Therefore,it is believed that the formation of hollow structure Au₁₄₄(SR)₆₀ cluster is due to the fact that the solid structure leads to a lower thermodynamic stability of the clusters(lowering the average cluster formation energy).More detailed results are given using Energy Decomposition Analysis(EDA),where calculations show that the small stabilization energy of the centrally located gold atom in Au₁₄₄(SR)₆₀ cluster mainly from the stronger Pauli repulsion energy between the central gold atom and the surrounding gold/ligand structure.These theoretical calculations reveal Au₁₄₄ is a very specific cluster in size and structure,which tends to form a hollow hollow structure rather than a solid filled conformation.Although the filling of gold atoms in hollow positions is an energetically favorable process,but leads to a larger atomic site resistance of the cluster and reduces the stability of the cluster.The second part:The structure and bonding properties of silver nanoclusters protected by N-heterocyclic carabine ligands were investigated by density functional theory,revealing the bonding nature of Ag-C bonds and determining the optimal carabine ligand coordination mode.Based on the experimentally synthesized Ag₂₉(BDT)₁₂(TPP)₄,the structure with the lowest formation energy was NHC-VI,which found among the six N-heterocyclic carabine ligands by ligand exchange and energy calculations.The bonding properties of Ag-C bonds on the cluster surface were further investigated by using Atoms in molecules analysis(AIM),bond level analysis and Energy decomposition analysis(EDA).The results showed the bonds of Ag-C formed by the ligand NHC-VI and the clusters belong to electrostatic covalent bonds and are more inclined to electrostatic bonds.