Novel Triphenylphosphine And Thiol Co-protected Ag-based Nanoclusters With Precise Dimension: Synthesis And Characterizations

Metallic nanoclusters with precise dimension have become focus issue of material science due to its linkage between organometallic complex and metallic nanoparticles.The controlable synthesis and characterization of nanoclusters are the basisc topics for understanding the relationship between their structures and properties at molecular level.The past decade have witnessed the prosperities of atomic precisely gold,silver,and its intermetallics nanoclusters with plenty of structures been fully determined by single-crystal X-ray diffraction.However,owing to the poor guideline and theory for the systhesis,the current research is still preliminary.Among the reported nanoclusters,silver-based nanoclusters with atomic precision have attracted increasing attention due to their fundamentally structure-related optical properties and potential applications in biotechnology.However,with insufficient exploration,developing new members of silver-based nanocluster with unique features and unreported numbers of metallic atoms still remains challenging.In this thesis,a series of silver-based nanoclusters was synthesized and characterized by employing thiol and triphenylphosphine as ligands The main content and new findings includes:1.A newly reported face-center-cubic(FCC)Ag₂₃(SCH₂CH₂Ph)₁₈(PPh₃)₈nanocluster was first synthesized by using 2-phenylethanethiol and triphenylphosphine as co-ligands.This synthetic system was further used as a protype for the exploration of Ag₂₃-derived Cu-Ag bimetallic nanocluster.Based on the influence of the Cu ions on the final products formation,face-centered cubic derived Ag₁₂Cu₂(SC₂H₄Ph)₁₂(PPh₃)₆ and Cu doped Ag₂₃(SCH₂CH₂Ph)₁₈(PPh₃)₈ nanoclusters were obtained by controlling the Cu/Ag molar ratio of the precursors in the range of 0?0.4 and 0.4?0.9,respectively.The nanoclusters were characterized by UV-visible spectroscopy,thermogravimetric analysis and single crystal X-ray diffraction.The presences of Cu in the nanoclusters were further verified by inductively coupled plasma massspectrometry and X-ray photoelectron spectroscopy.It is the first demonstration that Cu ions prefer to replace the Ag atoms in Ag₁₄(SC₂H₄Ph)₁₂(PPh₃)₈ nanocluster which directly coordinating with triphenylphosphine ligands.As a result,it lose the corresponding triphenylphosphine ligands to form Ag₁₂Cu₂(SC₂H₄Ph)₁₂(PPh₃)₆.Structural distortion was observed to balance the the dopping effect of Cu ion and the cavity induced by the corresponding absence of the triphenylphosphine ligands.2.By employing triphenylphosphine and 2-phenylethanethiol as ligand precursors,a new chiral Ag₃₃(SCH₂CH₂Ph)₂₄(PPh₃)₄ nanocluster with T point symmetry was synthesized in the presence of Pd regent for the first time.The obtained nanocluster was characterized by single crystal X-ray diffraction,nuclear magnetic resonance,inductively coupled plasma massspectrometry,X-ray photoelectron spectroscopy and electronic circular dichroism spectrum.DFT calculations were also perfomed to validate the structure and compositon of the nanocluster.Crystal structure of the nanocluster reveals that the nanocluster comprises an Ag₁₃ icosahedron core and a chiral shell framework of Ag₂₀S₂₄P₄ motif with structure adopted in T symmetries.A Pd-mediated synthesis scheme for Ag-based nanoclusters exploration was proposed based on the obtained results.This finding provides a new strategy for developing novel Ag-based nanoclusters.3.Based on the proposed Pd-mediated synthetic stragegy,we further employed different structure of thiol as the sulfydryl ligand for exploring the structure variation of Ag-based nanoclusters.Two kinds of Ag₂₇ nanocluster with different ligands protected,ie.Ag₂₇(SC₆H₁₁)₁₈(PPh₃)₂ and Ag₂₇(SC₈H₉)₁₈(PPh₃)_6,were obtained by using cyclohexanethiol and 2,4-dimethylbenzenethiol as sulfydryl ligand,respectively.The obtained nanoclusters were characterized by single crystal X-ray diffraction and inductively coupled plasma massspectrometry.The results revealed that both of the two nanoclusters featured with Ag₁₃ icosahedron core as structure motif and centrosymmetrally atomical arrangement of the kernel structures.The central Ag atom in Ag₁₃motif is the symcenter of the nanoclusters.Those observations demonstrated that there should be some relationship between the formation of Ag₁₃ icosahedron motif and the presence of the Pd reagent.Those structures could be further derived as Ag₂₆Pt(SC₆H₁₁)₁₈(PPh₃)₂ and Ag₂₆Pt(SC₈H₉)₁₈(PPh₃)₆ nanoclusters by replacing the Pd regent with a certain amount of Pt regent under the condition of the same ligands environment.4.A novel chiral Ag₁₈(?₈-S)(p-TBBT)₁₆(PPh₃)₈ nanocluster was synthesized from the ligands of p-tert-butylbenzylthiolate and triphenylphosphine by further employing the proposed Pd-mediated synthesis strategy.X-ray analyses revealed that the kernel of Ag₁₈S nanocluster can be regarded as core-shell structure,with an unprecedented octa-coordinated sulfido(?₈-S)atom featured Ag₈S crown-like structure as core and an S₈symmetral Ag₁₀S₁₆P₈ pseudo-octahedron cavity as shell.The atomic arrangement of the pseudo-octahedron cavity structure was meso and non chirality.However,the presence of Ag₈S induced the symmetry breaking from S₈ to C₄,and therefor endows the nanocluster chirality.If regarded the Ag₈S as the core and the meso-Ag₁₀S₁₆P₈ framework as the shell,the nanocluster could be classified as the first example of a core induced symmetrical breaking nanocluster with chirality.The presence of octa-coordinated sulfido atom is also verified by X-ray photoelectron spectroscopy and DFT calculation of the nanocluster.Steric effect of the tertiary butyl in the thiol ligands was found to be vitally important for Ag₁₈S formation,which concluded from the fact that only Ag₃₃ nanoclusters could be obtained from benzyl mercaptane,p-chlorobenzylthiolate or p-methoxy benzylthiolate instead of the p-tert-butylbenzylthiolate.