| In recent years,atomically precise metal nanoclusters have attracted great research interest as a new frontier in nanoscience research.Compared with the larger metal nanoparticles,these metal nanoclusters have some advantages:1)Their ultrasmall size(<2nm)endow them strong quantum size effects,which make them possess unique physicochemical properties,such as discrete energy levels of electrons,enhanced photoluminescence,extraordinary catalytic reactivity,and nonlinear optical properties.2)Their size can be controlled at atomic level,and we can obtain monodisperse metal nanocluster with exact atoms.This can help us further explore the relationship between size and properties,and also can offer some guidance for preparing new nanomaterials.3)Their total structures can be determined by single-crystal X-ray diffraction,which can help us further understand the arrangements of metal atoms,the arrangements of ligands,and the bonding between the ligands and the metal core.Hence,the relationship between structure and properties(e.g.,electronic,optical,catalytic)at the atomic level can be further explored.Among these nanoclusters,the thiolate-protected gold nanoclusters,denoted as Aun(SR)m,have attracted most widely attention on both their structure and properties.Recently,the selenolate-capped gold nanoclusters have been synthesized,and their properties have been studied.The results demonstrate that the selenolate-capped Aun(SeR)m nanoclusters possess better stability and different optical properties from those of the Aun(SR)m counterparts.But,due to the complicates process and low yield,there is still no crystal structure reported,which prevent the development of the Aun(SeR)m nanoclusters at certain extent.Herein,we developed a "co-reduction"method with high yield to obtain the Aun(SeR)m nanoclusters,and successfully obtained their crystal structures.Based on their structure,we also studied their optical properties,electrochemistry,catalytic performance and so on.Furthermore,we also employed the DFT calculation to further explore their properties.These results not only offer some experimental and theoretical basis for the Aun(SeR)m nanoclusters,but also provide more opportunities for the development of metal nanoclusters.The main content in this thesis includes:1.In this article,we present a facile,direct,synthetic approach of preparing monodisperse[Au25(SePh)18]nanoclusters in high yield,in which both PhSeH and NaBH4 should be added drop-wise to the solution of Au(Ⅲ)at the same time.Based on this,the structure of Au25(SePh)18 nanoclusters has been unambiguously determined for the first time.The selenolate-capped Au25 nanocluster shows noticeable differences from the previously reported Au25(SCH2CH2Ph)18 counterpart,albeit both share the icosahedral Au13 core and semi-ring Au2(Se/S)3 motifs.Furthermore,the electrochemical properties,catalytic performance,optical properties,and electronic structure also have been studied.These results indicate that the change of ligands has great effects on the electronic structure and the properties.2.With the co-reduction method,we obtained Au24(SeR)20 nanocluster and its crystal structure.It exhibits a prolate Au8 kernel,which can be viewed as two tetrahedral Au4 units cross-joined together without sharing any Au atoms.The kernel is protected by two trimeric Au3(SeR)4 staple motifs as well as two pentameric Au5(SeR)6 staple motifs,which looks like a "butterfly".Furthermore,the Au8 kernel and pentameric Au5(SeR)6 staple motif are also unprecedented,even in the thiolate-capped gold nanoclusters.This work provides a structural basis for understanding the gold-selenolate nanoclusters.3.Moreover,the coordination ability of the Se atom is stronger than that of the S atoms.So we use the selenol instead of the thiolate to synthesize the gold nanoclusters co-capped by the selenol and phosphine.And we successfully obtained the[Au60Se2(Ph3P)10(SeR)15]nanocluster and its atomic structure.This structure contains five icosahedral Au13 building blocks bridging with "Au-Se-Au",which looks like a closed gold ring.It worth note that two Se atoms(without the phenyl tail)locating at the center of the nanocluster are exist in the formation of Se-(Au)5,which is not reported in previous gold nanoclusters.In addition,the optical and electrochemical properties were studied,which shows that the electronic properties of the icosahedral Au13 units still remain unchanged in the Au60 nanocluster.4.Through the optimization of conditions,we successfully synthesized the rod-like[Au25(PPh3)10(SePh)5Cl2]q(q = +1 and +2)nanoclusters.And their crystal structures also been determined,which possesses two icosahedral Aui3 units(sharing a vertex gold atom).In this system,we fully studied that how the single electron affects the properties of the rod-like AU25 nanoclusters.Compared with the spherical AU25 system("superatom"),the changes in the rod-like Au25 nanoclusters("non-superatom")have some difference.But their fundamental principle is similar.This work offers new insights into the relationship between the properties and the valence of the "non-superatom" gold nanoclusters。5.Under the reduction condition,the Au25(SePh)18 nanocluster will be converted into the[Au25(SC2H4Ph)18]-nanoclusters through ligand-ex change.This finding is quite remarkable due to stronger bond of Au-Se in comparison to Au-S of the final product.Results show that the presence of the reducing agent merely initiates transformation of[Au25(SePh)18]-to the[Au23(SePh)16]-by pulling out two units of"Au-SeR".Moreover,the[Au23(SePh)16]-nanoclusters can be converted into co-protected(Se&S)AU25 nanocluster with excess PET ligands,and the process of the ligand-exchange can be controlled by the reductant.This reaction mechanism first reported in the synthesis of the gold nanoclusters.This has significant contribution to understand and further explore the mechanism of ligand-exchange. |
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