Effects Of Building-blocks On Structu Res And Properties Of Self-assembled Coinage Metal Nanoclusters

Atomically precise metal nanoclusters are of significant importance in the nanoscience.In the field of metal nanomaterials,controlling the shapes and structures of metal crystals has proved to be a powerful means for tailoring their properties for wide applications.To achieve desirable shapes of metal nanocrystals,significant efforts have been made in developing new strategies for their shape-controlled synthesis.Among these approaches,the use of specific capping ligands to control the exposed surface of metal nanocrystals is an effective strategy.Though a wide variety of capping agents have been used in controlling the shapes of metal nanocrystals,it is still unclear how these capping ligands work in terms of their binding capabilities and selectivities toward a specific metal surface and their effects on the size and shape of the resulting nanocrystals.Due to their nature of monodispersity at the molecular level,atomically precise metal nanoclusters are readily crystallized into single crystals for resolving their total structures,including the detailed binding modes of surface ligands.Systematic investigations of the structures of metal nanoclusters can thus shed light on the atomic details of the early,or embryonic stages of the growth of metal particles,thereby allowing studies of how capping ligands control the shape evolution of metal nanocrystals.In recent years,the growth mechanism of organometallic nanoclusters has been extensively studied.Teo’s group reported the growth patterns"cluster of clusters".A series of gold nanoclusters with "tetrahedral unit assembly and growth" mode were firstly discovered by Jin’s group.Zheng’s group reported that silver nanoclusters grow through the "assembly of face-centered cubic units".Although the growth mode of metal nanoclusters has been widely studied,it is still unknown whether there are other ways or other assembly units for the growth of metal nanoclusters.In this paper,by screening the synthesis conditions,Ag40,Ag43,Ag46,Pt3Ag33,Pt3Au12Ag2i,Au25-xCux and CU3AU34 nanoclusters were synthesized.By studying the growth and transformation process of Ag40 to Ag46,we found a new growth mode of metal nanoclusters,"core filling",and the core structure is critical to the optical absorption of the clusters.By comparing the Ag46,Ag67 and Ag88 nanoclusters,we experimentally confirmed Hakkinen’s "Ag21S8 unit growth"pattern.In addition,we synthesized the Pt3Ag33 nanocluster.Through the precise comparison of PtiAg12 and Pt2Ag23 nanoclusters,we found that the optical absorption and photoluminescence of metal nanoclusters gradually red shifted with the increase of PtiAgi2 assembly unit.At the same time,we compared Au25-xCux and Cu3Au34 nanoclusters and found that the change of assembly unit also had a strong effect on the optical absorption.The research content of this paper is as follows:1.Understanding the optical properties of nanoclusters is one of the central tasks in fundamental research.In this work,three new silver nanoclusters Ag40,Ag43 and Ag46 are achieved.Ag40 and Ag46 nanoclusters have distinctly different cores but a common protecting shell.Significantly,the Ag40 nanocluster comprises a simple cubic core of Ag8,which is for the first time observed experimentally.Using the Ag40 and Ag46 nanoclusters as a unique pair,we have investigated the effect of core structure on the optical absorption properties of these nanoclusters.The compact core-shell structure in Ag46 makes the frontier orbitals highly degenerate,whereas the loose core-shell of Ag4o leads to much less degeneracy.In addition,we have also realized the transformation from Ag40 to Ag46 nanocluster by using the ligands exchange method,in which an intermediate silver nanocluster,Ag43,has been unraveled.Overall,this work reveals that the core-shell packing mode plays a significant role in determining the optics of metal nanoclusters.The new materials with controlled crystalline phases also hold promise in other applications.2.The 13-atom icosahedron is a ubiquitous building block in cluster materials.In this work,we report a controlled self-assembly of three M13 icosahedral building-blocks into cyclic Pt3Ag33 or Pt3Au,2Ag2i nanoclusters.The structures of these two M36 nanoclusters(M=Pt/Ag/Au)are determined by X-ray crystallography.Both bimetallic and trimetallic M36 nanoclusters comprise a core of 36 metal atoms,which is protected by 8 chlorides and 12 PPh3 ligands.The Pt atoms are doped into the respective centers of the three constituent M13 icosahedra.In the trimetallic nanocluster,the third metal(i.e.,Au atoms)selectively substitutes the top sites of the Pt3Ag33 nanocluster that are bonded with the PPh3 ligands.Compared to the previously reported 25-atom Pt2Ag23 and the 13-atom Pt,Ag12 nanoclusters,the Pt3Ag33 nanocluster exhibits a red-shift in both the optical absorption and photoluminescence due to the assembly of an additional Pt1Ag12 icosahedron and the resultant electron delocalization.In addition,a counteractive effect is found on the luminescence of the trimetallic M36 nanocluster.3.Herein,we report the synthesis and atomic structure of the cluster-assembled CuxAu25-x and Cu3Au34 nanoclusters(NCs).The atomic structures of both NCs were precisely determined by single crystal X-ray crystallography.The CuxAu25-x NC was assembled by two icosahedral M13 via vertex-sharing mode.The Cu atoms partially occupy the top and waist sites and are mono-coordinated with chlorine or thiol ligands.Meanwhile,the Cu3Au34 NC can be described as three 13-atom icosahedra sharing three vertexes in cyclic fashion.All the three Cu atoms occupy the internal positions of the cluster core and are mono-coordinated by the bare S atoms in Cu3Au34.The absorption spectra of the as-synthesized bimetallic NCs reveal that the additional-metal-doping and the different cluster-assembly affect the electronic structure of the monometallic NCs.4.We took styrene oxidation reaction as the model reaction to study the catalytic performance of nanoclusters,and we found that the alloy nanoclusters had better catalytic activity:compared with Au25/CNT catalyst,the bimetallic nanocluster Au25-xAgx/CNT catalyst had higher selectivity.Meanwhile,compared with Ag44/CNT catalyst,bimetallic nanocluster Au25-xAgx/CNT catalyst has a better conversion.In addition,water can change the selectivity in the oxidation of styrene.We studied the action of water in styrene oxidation reaction through comparative experiment.