Syntheses,Structures And Bioapplications Of Noble Metal Clusters Protected By Rigid Bulky Ligands

Metal nanoclusters with sizes consisting of tens to hundreds of atoms is a special class of materials.Nanoclusters are unique because they can be expressed in clear molecular formulas.Their ultra-small size?metal core diameter from sub-nanometer to 2-3nm?places them between small molecules?for example,metal-ligand complexes?and plasma metal nanoparticles.With the help of X-ray single crystal diffraction technique,the atom-precise single crystal structure can be obtained.In the thesis,a series of silver or rich silver bimetallic nanoclusters with different sizes were successfully synthesized by using 1-adamantanethiolate as a surface-protecting ligand and characterized by X-ray single crystal diffraction.At the same time,we also studied the optical properties,surface reaction properties and bioapplication.The main results and findings of this thesis are summarized as follows:1.Rigid bulky thiolate-protected silver nanoclusters:?a?A heavily twinned metal nanoparticle containing 141 silver atoms,[Ag141Br12?S-Adm?40]3+,was successfully synthesized by using bulky 1-adamantanethiolate.The nanoparticle can be structurally described as a multiple-twinned Ag71 short nanorod core terminated by an Ag-SR/Br complex shell.Compared to previously reported thiolate-stabilized noble metal nanoclusters,first,the Ag71 core has twenty tetrahedral crystalline domains,while it adopts a non-perfect spherical geometry but not an icosahedron,serving as an excellent structure model to visualize the multiple-twinned nanostructured of face-center cubic metals at the molecular level.Second,a low surface coverage of thiolates is associated with the multiple-twinned feature of the core,suggesting the importance of surface ligands in controlling the shape of metal nanocrystals.More importantly,the low surface coverage of thiolates gives rise to high surface reactivity toward ligand exchange,thereby creating excellent water solubility and biocompatibility nanoclusters.The use of bulkly ligands contributes heavily-twinned metal nanoparticles with high surface reactivity.The finding is expected to apply to the synthesis of bigger nanoparticles,resulting in high surface reactivity of metal nanoparticles.?b?A fivefold twinned nanostructures,Ag213Cl33?S-Adm?44,was successfully obtained by introducing a monodentate phosphine ligand simultaneously into the reaction system.As miniatures of fivefold twinned nanostructures of fcc metals,the success in resolving the total structures of Ag213 nanoparticles using single-crystal X-ray diffraction provides important models to visualize at the atomic scale the adding twinned defect facets in ideality inside fivefold twinned nanostructures of fcc metals and to describe their detailed surface sturctures.As miniatures of fivefold twinned nanostructures of face-centred cubic metals,adding the twinned defect facets is the readily discernible compensation for the solid-angle deficiency of the fivefold twinned Ag116 core,as different to a subtle distortion of Ag136,increasing our understanding of the fivefold twinned nanostructures.Second,as we saw in the Ag141 structure,the steric hindrance of the 1-adamantanethiolate makes the nanoparticle a low surface coverage of thiolates.This special surface structure results in a high surface reactivity,so we confirmed further the previous experimental results in Ag213 system.Compared with Ag141,a higher surface reactivity can be attributed to its lower surface coverage of thiolates.2.Rigid Bulky thiolate-protected bimetallic nanoclusters:Bimetallic nanoclusters,?PtAg?29,?AuAg?67 and?AgCu?56,were successfully synthesized by reducing two different metal precursors in same system.As revealed by X-ray single-crystal analysis,the M,3 core of?PtAg?29 that is different from the previously reported icosahedron is an FCC kernel.Multiple tetrahedral motifs are identified in the bimetallic nanoclusters,such as the surface motif,the integrated motif shell and the overall metal framework.Such a bimetallic nanocluster exhibits strong red flurescence in the ultraviolet light,and we successfully used it as a fluorescent probe for tumor cell imaging.Although we did not obtain the single structure of?AuAg?67,its molecular composition,[AuxAg67-x?S-Adm?35]2+?x=6?24?,was confirmed by mass spectrum that was a mixture of a series of different doping Au atoms?AuAg?67.The nanocluster in the mass spectrum shows two Gaussian distribution which is different from single Gaussian distribution mass spectrum of previously reported bimetallic nanoclusters.For the?AgCu?56 bimetallic nanocluster,their structural characteristic of the bowl resulted in some low coordination or unmetric metal atoms on the surface,combined with Cu in the CO₂ reduction showed good catalytic activity,made it had potential application in CO₂ reduction.