Research On Synthesis,Structures And Metallic States Of Large Coinage Metal Nanoclusters

Coinage metal nanoclusters(1-3 nm,gold,silver and coper)have atomically accurate structures,which are bridges connecting organometallic molecules to metal nanoparticles.Due to the existence of quantum confinement effect,small-sized naoclusters have discrete energy levels and exhibit molecular behavior,while large-sized nanoclusters have continuous energy bands and exhibit strong surface plasmon resonance like metal nanoparticles.The transformation process from molecular to metallic has always been a fundamental concern in the nano science,and naoclusters with a suitable size range and well-defined structure are the key to answering this question.Therefore,it is important to establish the boundary of metallic states at the atomic level and to study the factors that affect the metallic states,which can further understand the generation of metallic bonds and the formation of plasmon resonance.However,the synthesis and accurate structure determination of larger nanoclusters are difficult,and most of the known larger nanoclusters are protected by thiolate ligands.The development of larger alkynyl-protected nanoclusters is beneficial to broaden the types of nanoclusters,narrow the boundary of metallic states,and study the factors that affect metallic states.In response to the above problems,we used alkynyl ligands,chloride ligands,phosphorus ligands and thiolate ligands as surface passivation groups to develop a method of directly reducing the precursor using a weak reducing agent,and synthesized several novel larger structures of gold,silver nanoclusters and heterometallic silver-copper nanoclusters.Their structures and properties were characterized accordingly.The specific research contents are as follows:As far as the problem of polydispersity and difficult crystallization of the reduced product,we used diphenylsilane with weak reducibility as a reducing agent to prepare alkynyl-protected metal nanoclusters.This method has been successfully used in the synthesis of gold,silver and silver-copper nanoclusters,and has been proved to be universal for the synthesis of alkynyl-protected metal naonclusters.The kernel structures of these nanoclusters and the coordination modes of the peripheral alkynyl ligands are very novel,which are quite different from the nanoclusters protected by thiolate ligands.We further study the metallic states of larger metal nanoclusters.It was unexpectedly found that the rod-shaped structure helps the nanoclusters to exhibit metallic electron dynamics at relatively small sizes,and that the electron dynamics are wavelength dependent of the pump laser.Meanwhile,comparing the optical absorption of spherical and rod-shaped plasmonic silver nanoclusters,it is found that the rod-shaped structure induces SPR splitting.Furthermore,the scale range of SPR splitting of silver nanoclusters is accurately determined.The work of this thesis provides a new idea for the future research on the synthesis,structure and metallicity of larger metal nanoclusters.