Synthesis And Properties Of Four Medium-sized Gold Nanoclusters

In recent years,great progress of thiolate-protected gold nanoclusters(TGN)has been achieved in the synthesis,structure,property,properties and application research.By now a number of novel Aun(SR)m clusters such as Au25(SR)18,Au36(SR)24,Au38(SR)24,Au102(SR)44 and Au144(SR)60,have been synthesized by wet-chemistry method and structurally determined by X-ray crystallography,which showed potential applicaton in a wide range of fields such as biomedicine,catalysis,sensing,etc.The structure control of gold nanoclusters at atomic level is critical to understand the relationship between the composition(structure)and property.Recently,we synthesized four novel medium-sized gold nanoclusters,and studied the relationship between their structures and properties.The points of the thesis are shown as follows:1.The 18-electron shell closure structure of Au nanoclusters protected by thiolates had not been reported until the start of this work.For the first time,we synthesized a novel nanocluster(Au44(2,4-DMBT)26,2,4-DMBTH = 2,4-dimethylbenzenethiol)with the 18-electron shell closure structure.The composition and structure were determined by using multiple techniques such as mass spectrometry,TGA,XPS and single crystal X-ray crystallography(SCXC).Compared with another structurally resolved nanocluster Au44(TBBT)28(TBBTH = 4-tert-butylbenzenelthiol),the new cluster bears the same gold atom number but a different thiolate and structure(Au44(2,4-DMBT)26 is of non-fcc structure,whereas Au44(TBBT)28 is fcc-structured.).Although Au44(2,4-DMBT)26 bearing a 18-electron shell closure structure,it is less thermostable than Au44(TBBT)28,indicating that some other factors like atom packing also contribute to the thermostability of gold nanoclsuters.X-ray photoelectron spectroscopy showed that the charge state of Au in Au44(2,4-DMBT)26 is remarkably more positive than that in Au44(TBBT)28,even slightly more positive than the charge state of gold in Au-(2,4-DMBT)or Au-TBBT complexes,which indicates that the structure of gold nanoclusters influences the charge state of gold.2.Structural isomerization is an important concept in organic chemistry and it is recently found to be applicable to thiolated gold nanoparticles.However,to the best of our knowledge,the isomerization with the kernel structure of the cluster changed while maintaining fcc packing was not previously found.Here,we synthesized a novel gold nanocluster(Au52(PET)32,PET = phenylethanethiolate)via a modified acid induced synthesis method.SCXC reveals that both the as-obtained novel Au52(PET)32 and the well-known Au52(TBBT)32 have fcc structure.However,in their fcc structures,gold atoms are arranged by different patterns.Given no consideration of the ligand difference,they can be regarded as a pair of fcc structure isomers.As a result of fcc structure isomerization,Au52(PET)32 has remarkably different UV/vis/NIR absorption from that of Au52(TBBT)32.Another interesting finding in this work is that the kernel of Au52(PET)32 has high-indexed facets(311),which is not previously reported in the structures of gold nanoclusters to the best of our knowledge.3.It was unknown if the inner kernel-outer staples match is a key-lock match and how the surface staples influence some of the properties of metal nanoclusters.Herein,we developed an acid-induction method for synthesizing a novel gold nanocluster Au42(TBBT)26 whose composition and structure were determined by ESI-MS and single-crystal X-ray crystallography(SCXC).SCXC also revealed that Au42(TBBT)26 has an identical kernel Au34 but different staples with an existing gold nanocluster Au44(TBBT)28,indicating that the kernel-staples match is not a key-lock match and the existence of homo-ligand-homo-kernel-hetero-staples phenomenon in metal nanoclusters.Further experiments revealed that the decrease of two Au-SR units results in the significant reduction of stability and fluorescence intensity of Au42(TBBT)26.These results indicate that the staples greatly contribute to the stability of gold nanoclusters and influence their photoluminescence intensity.4.Although face-centered cubic(fcc),body-centered cubic(bec),hexagonal close-packed(hcp)and other structured gold nanoclusters had been reported,it was still unclear if gold nanoclusters with mix-packed kernels exist,and the correlation between kernel packings and the properties of gold nanoclusters was unknown before we began this study.Herein,a novel Au49(2,4-DMBT)27 nanocluster with shell electron count of 22 was synthesized and structurally resolved by single-crystal X-ray crystallography(SCXC),which revealed that Au49(2,4-DMBT)27 contains a unique Au34 kernel consisting of one quasi-fcc-structured A1121 and one non-fcc-structured Au13 unit.Such a dual-packed structure has not been previously reported.Interestingly,further experiments revealed that the kernel packing greatly influenced the electrochemical gap(EG)and that the fcc structure possessed a larger EG than the investigated non-fcc structure when they have similar sizes.