Theoretical Study Of Interaction Between Ligands And Gold Clusters

Clusters have the sizes between those of atoms and macroscopical systems, and have many unique properties. So many experimental and theoretical researches have been done on them. Even more focuses have been put on gold clusters, which have many unique properties. Ligand-stabilized gold clusters have the extraordinary stability and many unique physicochemical properties, which can be"tuned"through chemical modification and choice of the passivating ligands. Along with the rapid development of computational methods and computer technology, now computational chemistry is possible to study geometry, electronic structures and many other properties of clusters from first-principles calculations. And due to its moderate computational consume and high precision, density functional theory (DFT) has become one of the most important methods in quantum chemistry. This dissertation is to study the properties of ligand-stabilized gold clusters from DFT method and focus on the interaction between ligands and clusters.In Chapter 1, we give a brief introduction to clusters firstly. Then, some common methods in experimental and theoretical studies on clusters are discussed. Then, we expatiate the significance and the challenge in the research of ligand-stabilized gold clusters and introduce the main works of gold clusters in experimental and theoretical studies in detail. At last, we simply describe the purpose of our work on gold clusters.In Chapter 2, we introduce the progress of quantum chemistry. In the fundament of DFT, Kohn-Sham equation is introduced in detail. In addition, we introduce several functionals, TDDFT, the relativistic effect, and the natural bond orbital (NBO), which are often considered and used in this thesis. As last, we carry out test calculations on well-defined small molecule to determine the optimum method in the study of gold clusters. In Chapter 3, we investigate the stability of gold cluster in detail and suggest the factors impacting the stability of gold clusters. In addition, we have studied the Au₁₃⁵⁺ to testify the factors. At last, we introduce some methods to denote the stability of gold clusters in experimental and theoretical studies.In Chapter 4, we investigate the mechanism of interaction between ligand and gold cluster in detail. Firstly, we confirm the type of ligand adsorption on gold cluster. Then, we investigate the geometric structure, the frontier orbital, NBO analysis and energy decomposition analysis (EDA) of the complex WAu₁₂PH₃, and gain the mechanism of interaction. In addition, we investigate the geometries and Au–P bonding of [MAu₁₂]qPR₃, which is changed in different ligands and clusters. The ligand with strong ability ofσdonor is prone to interact with the gold cluster with high positive charges. At last, we investigate the correlation between the interaction and the distance of Au–P bond.In Chapter 5, we investigate the complexes [Au₁₃(PMe₂Ph)₁₀Cl₂]³⁺ and [Au₂₅(SR)₁₈]^–, which have the same core Au₁₃⁵⁺ and different ligands. Firstly, we have studied the geometric structures, the frontier orbitals, and energy decomposition analysis (EDA) of the complexes to gain the mechanism of interaction between ligand and gold clusters. In the complexes, Cl^– ligand withdraws charges from the gold core. And phosphines and thiol ligands attach on the gold core asσdonor, which coordinate to the gold core surface by dative bonds. The ligand with strong ability of electron donor should be chosen to stabilize the clusters. At last, we investigate the electronic spectrum of the two complexes, which are composed of the transition between the gold core and the ligands.In Chapter 6, we investigate the complexes Au₂₀(PR₃)₄ in detail. Firstly, we have studied the geometric structure and stability of Au20 cluster. Then, the different adsorption types in the complex are investigated. And we investigate the geometric structure, the frontier orbital and the EDA to explain the difference in two types. At last, we investigate the electronic spectra of the complex, which is composed of the transition from the gold core to the ligand. In Chapter 7, we investigate the complexes [Au₅₅(PPh₃)₁₂Cl₆]^– in detail. The Au₅₅⁵⁺ core in different geometric structures is investigated. We investigate the Au₅₅⁵⁺ core as a Au₁₃⁵⁺ embedding a Au32 cluster and take the bond energy between Au₁₃⁵⁺ and Au32 to denote the stability of Au₅₅⁵⁺. Then, we have studied the geometric structure, electronic configuration and EDA of the complex. At last, we investigate the electronic spectra of the complex, which is composed of transition in the gold core.