Synthesis/Characterization And Properties Of Ligand Protected Coinage Metal Nanoclusters

Nanoclusters are ultrasmall nanoparticles with precise composition and well-defined structures.In comparison with nanoparticles,nanoclusters are special because of their discrete engery levels,monodispersity,atomically precise structures.Metal nanoclusters have wide applications in catalysis,biosensors and molecular devices etc.Nanoclusters can offer models for theoretical calculation to assist in understanding the electronic structure,and they are helpful in studying catalytic mechanisms,designing and synthesizing catalysts.The barriers that hinder the development of nanocluster chemistry are low yields,low stability,and limited structural models.In order to solver the above-mentioned problems,this dissertation focuses on increasing the stability and generating the diversity of nanoclusters,and testing their application in catalysis.We used multidentate ligand(PhPpy2)as a protection in synthesizing gold nanoclusters.For the first time,we reported a structurally determined Au20 cluster that consists of two Au11 units.Secondly,by using a tetradentate ligand PP3,we synthesized a new type of Au20 nanocluster featuring chiral inorganic metal kernel.By comparing the structures and optical properties of doped and undoped nanoclusters,we can understand the role of the doped atoms at atom level.We developed a direct reduction method to prepare alkynyl-protected gold nanoclusters.We could precisely control the ratios between ligands and metals by using neat gold compounds as precursors.A series of alkynyl-protected Au,Au/Ag,Au/Cu nanoclusters have been synthesized and structurally determined.We found that the coordination manners of PhC?C on the surface of nanoclusters include V shaped PhC?Au-(PhC2)-Au-C?CPh "staple",L shaped hOC?Au-C?CPh "staple",and simple bridge motifs,all through the ?-? bonds between the PhC=C groups and metal atoms.It indicates that the "staple" unit maybe a common motif in nanoclusters.In addition,theoretical calculation suggested that the PhC?C groups actively participate in the frontier orbitals of the whole nanocluster.We found that ligands could influence and even determine the formation of the cluster structures.We also reported an alkynyl-protected Au24 cluster emitting near infrared(NIR)light(QY=12%)under irradiation,and we studied the frontier orbitals and the origin of NIR by theoretical calculation.In general,both of the alkynyl protected Au/Ag and Au/Cu nanoclusters are made up shell by shell.Compared with Au/Ag nanoclusters,the binding modes of the RC?C in Au/Cu nanoclusters are more complex.The direct reduction method also can be used in synthesizing a series of thiolate and phosphine co-protected gold nanoclusters.Meanwhile,we studied the effect of Cl in synthesis,and synthesized two new Au38 clusters.These two isostructural nanoclusters can be served as an ideal model in studying the effect of ligands.In the end,we investigated the catalytic performance of two Au38 nanoclusters with different protecting ligands in the semhydrogenation of alkynes to alkenes.We found that the alkynyl-protected Au38 would promote the reaction,however,the thiolated Au38 did not work,which emphasizes the importance of ligand.When considering the steric effect,the hydrogenation of internal alkynes is a process of activation of H2 rather than alkynes.