| Atomically precise noble metal(mainly silver and gold)nanoclusters are an emerging category of promising functional materials for future applications in energy,sensing,catalysis,and nanoelectronics.These nanoclusters are protected by ligands such as thiols,phosphines,and hydride and have sizes between those of atoms and plasmonic nanoparticles.Thiolate-protected gold nanoparticles(AuNPs)are a special class of nanomaterials that form atomically precise NPs with distinct numbers of Au atoms(n)and thiolate(-SR,R = hydrocarbon tail)ligands(m)with molecular formula[Aun(SR)m].These are generally termed Au nanomolecules(Au NMs),nanoclusters,and nanocrystals.Au NMs offer atomic precision in size,which is desired to underpin the rules governing the nanoscale regime and factors affecting the unique properties conferred by quantum confinement.Research since the 1990s has established the molecular nature of these compounds and investigated their unique size-dependent optical and electrochemical properties.Pioneering work in X-ray crystallography of Au102(SC6H4COOH)44 and Au25(SC2H4Ph)18-revolutionized the field by providing significant insight into the structural assembly of Au NMs and surface protection modes.With the well-defined structures,the related properties can be achieved and utilized for various applications,including catalysis,bio-application,photochemistry,magnetism,and energy conversion.In metallurgy,the properties of a pure metal are modified by the addition of other metals,which often offers augmented characteristics,making them more utilizable for real-life applications.Recent studies have shown that the physicochemical properties of alloy NCs could be critically improved compared to those of the single component systems.Metal alloys exhibit functionalities unlike those of single metals from the viewpoint of creating new functional nanomaterials.In gas phase cluster research,generated alloy clusters can be spatially separated with atomic precision in vacuum.Thus,the influences of increases or decreases in each element on the overall electronic structure of the cluster can be elucidated.However,to further understand the related mixing and synergistic effects,alloy clusters need to be produced on a large scale and characterized by various techniques.Because alloy clusters protected by thiolate(SR)can be synthesized by chemical methods.Generally,the synthetic methods for the reported alloy NCs protected by thiolate ligands can be categorized into three types.First,the "one-pot" approach was widely used because of its operational simplicity,in which all requisite reagents were mixed together.Second,the metal-exchange strategy utilizing the reaction of the templated,atomically precise metal NCs with foreign metal atoms or metal-SR complex.The third is two-phase ligand-exchange approach,similar to the metal exchange approach,the ligand-exchange approach needs template alloy NCs to react with other ligands,which generally occurs under the two-phase circumstances.However,traditional synthetic methods are limited by the certain randomness in the synthesis of metal nanoclusters.Inspired by the simplicity of the one-pot method and the effectiveness of the two-phase ligand-exchange approach,we tried to explore a combinative synthetic strategy,i.e.,the in situ two-phase ligand-exchange method.The goal is to synthesize atomically precise alloy nanoclusters with high yield,especially for the series of alloy nanoclusters or functional nanoclusters.The main content in this thesis includes:1.A new method termed "in situ two-phase ligand exchange" was developed to obtain alloy nanoclusters.With this approach,a series of alloy nanoclusters were obtained for the first time,including Au20Ag1(SR)15(NC-1),Au21-xAgx(SR)15(NC-2,x?4-8),Au21-xCux(SR)15(NC-3,x=0,1),and Au21-xCux(SR)15(NC-4,x?2-5)(R=tert-butyl).Interestingly,single-crystal X-ray crystallography(SCXRD)shows that their frameworks are all alike except for NC-4,indicating that more Cu dopants alter the structure.NC-4 exhibits a significantly different configuration.The optical absorption spectra of these bimetal nanoclusters(NCs)show distinct characteristic peaks,indicating that the metal-doping remarkably affects the electronic structure of NCs.The DFT calculations were also employed for determination of NC 1-3 frameworks and understanding their optical properties.Of note,the homo-gold nanocluster,that is Au2i(SR)15(NC-5),also has been synthetized using the in situ method and NC-5 has a similar structure to that of NC 1-3.2.Ultrasmall nanoclusters(e.g.,Au15)are crucial in not only real applications such as bio-application but also in understanding the structure transition from gold complexes to gold nanoclusters.However,the determination of these transition-sized gold nanoclusters has long been a major challenge.In this work,two new nanoclusters in the transition regime,including the thus far smallest thiolated alloy nanocluster Cd1Au14(StBu)12(NC-6)and Cd1Au14(S-Adm)12(NC-7),are obtained and their atomic structures are fully determined by single crystal X-ray diffraction.Moreover,based on the structures of CdiAul4(SR)12 and Au16(SR)12,we perform DFT calculations to predict the structure of the "transformation" nanocluster,Au15(Au15(SR)12-and Au15(SR)13).Overall,this work bridges the gaps between gold complexes and nanoclusters.3.In this work,we report the synthesis and crystal structure of Au38-xCux(2,4-DMBT)24(NC-9,x=0-6,2,4-DMBTH = 2,4-dimethylbenzenethiol)alloy nanocluster for the first time.A variety of characterizations including ESI-MS,TGA,and XPS reveal the composition as NC-9.The single crystal structure has been determined by an X-ray single crystal diffractometer.From the anatomy of the structure,a bi-icosahedral Au23 core is protected by six dimeric[-SR-M-SR-M-SR-]units(M = Cu/Au)and three monomeric[-SR-Au-SR-]units.It is interesting that all the Cu atoms are selectively doped in the motifs of the NC-9 nanocluster.This phenomenon is distinct from the exclusive core doping of the Ag atoms in the previously reported Au38-xAgx(SR)24 alloy.Both the experimental results and DFT calculations of UV-vis spectra imply that the optical property of the Au38-xCux(2,4-DMBT)24 nanocluster is consistent with that of the Au38(2,4-DMBT)24(NC-10)nanocluster,because the Cu dopants make little contribution to the frontier orbitals of the alloy NC.4.Compare with S,Se,Te,the Au/Ag NCs protected by O are less due to the small radius and hard Lewis basicity of the O atom.However,the metal-chalcogen interfaces will induce diverse properties due to differences in O,S,Se and Te.Therefore,we are motivated to purse the M-O interface and gain the novel nanoclusters with the special performance.The introduction of sulfonate could be more applicable,as the soft S atom could easily adjust the coordination environment around the 0 atoms.After careful screening of the reaction conditions,we synthesize a new Ag-Cu bimetallic nanocluster,[Ag54-xCuxS19(tBuS)20(tBuSO3)12]2+(NC-8,X=8-20).The crystal structure reveals that the alloy cluster consists of a Cu10Ag2S7 core,a M42(tBuS)20(tBuSO3)12 shell and other 12 bare S atoms.The bare S and thiolate ligands have been previously observed in Ag or Ag-alloy NCs,while the sulphonate ligand is observed in NCs for the first time via in situ oxidation of thiolate,which sheds light on the interface of nanocluster-sulphonate and offers a potential strategy for the development of new nanoclusters with applicable properties. |
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