Structure Modulation And Optical Properties Of Nested Polyhedral Silver Clusters

Metal clusters,with their atomically precise structures,can be used as models to correlate precise relationships between microscopic substances and macroscopic properties.As a typical representative of metal clusters,silver clusters not only possess rich electronic and geometric structures,but also exhibit unique physicochemical properties,providing valuable opportunities for interdisciplinary research among chemistry,mathematics,physics,and materials science.Over the past decades,researchers worldwide have established various mature synthetic strategies,constructing a rich variety of silver cluster structures.However,the majority of currently synthesized silver clusters lack typical polyhedral features.The controllable synthesis of polyhedral silver clusters remains a formidable challenge due to the difficulty in precisely shaping silver polygons and polyhedral shells.Motivated by these considerations,several nested polyhedral silver clusters have been designed and synthesized in this dissertation by combining anion template strategy and surface ligand engineering.The structures have been dissected from the perspectives of both chemistry and geometry,and their solution behaviors and optical properties have been investigated using in situ characterization techniques.The primary research endeavors encompass the following:I.Synthesis and optical properties of nested polyhedral silver clusters with dual silver shellUsing an anion template strategy in combination with the regulation of the type sulfonic acid ligands,a pair of silver clusters with similar characteristics,Ag45 and Ag51,have been successfully synthesized.These two clusters exhibit a typical nested structure,featuring comparable Ag42 shells but significantly distinct kernels,where the building units of the Ag42 outer shell exhibit features reminiscent of Johnson solids.The phenomenon of accommodating different kernel structures in similar shells highlights the flexibility of the shell structures.Due to the difference in the kernel structures,Ag45 and Ag51 showcase diametrically opposite NIR photoluminescence behavior with decreasing temperature.This marks initial documentation of a closely related pair of silver clusters exhibiting inverse luminescence characteristics.In addition,we have also synthesized a 60-nuclear silver cluster consisting of an Ag14 rhombic dodecahedron kernel and an Ag46 outer shell.This diverges significantly from the previously documented Ag60 cluster,which consists of an Ag12 cuboctahedron kernel and an Ag48 outer shell.It is interesting to note that the nested structure rearrangement imparts distinct luminescence performances.This work achieves effective modulation of the luminescence properties of silver clusters and lays a solid foundation for the exploiting future applications.II.Nested polyhedral silver clusters with incompatible symmetryBy employing a blend anion template strategy and surface ligand engineering,we have successfully isolated two Ag90 clusters with similar structures but different space groups under solvothermal conditions by elaborately selecting S2-and PO43-anions as well as tBuSH and PhPO3H2 ligands.The spherical Ag90 cluster with overall pseudo-Th symmetry is comprised of three concentric silver polyhedra that exhibit seemingly incompatible symmetries.In detail,the inner and middle shells exhibit octahedral symmetry,represented by an octahedron(a Platonic solid)and a truncated octahedron(an Archimedean solid),respectively,while the outer shell displays icosahedral symmetry,taking the form of a rhombicosidodecahedron(another Archimedean solid).The Ag90 cluster reconciles this apparent incompatibility by employing the two-and threefold axes arrangement,reminiscent of the configuration found in the Keplers Kosmos model formulated by the John Conway.Ⅲ.Synthesis and geometric analysis of a Keplerate polyhedral silver clusterOn the basis of the second work,by further modulating the types of heteroanionic templates and surface ligands,we successfully achieved the self-assembly of the Keplerate polyhedral silver cluster Ag192.Notably,Ag192 stands out as an exceptionally symmetric silver cluster,featuring six silver shells and fourteen anion shells.Almost all of the twenty concentric shells are either Archimedean or Platonic solids,with only one exception.Each of these shells exhibits either tetrahedral or octahedral symmetry,and is oriented in such a manner as to maximize the presence of their four-,three-and two-fold axes.Nevertheless,the majority of the edges of these silver and anion shells are excessively long to be considered representative of bonds.Importantly,a supershell is created from the initial three anion shells with a rhombic dodecahedron configuration,which seives as the cornerstone for the overall silver cluster structure.Following this,individual silver ions are located within adjacent anionic cavities,effectively filling the space.In a parallel manner,individual anionic groups reside within adjacent cationic cavities,predominantly homogeneous polyhedra that also occupy space.The self-assembly of Ag192 was finally in the manner described above.IV.Polyhedral silver cluster encapsulating ultra-small nanocrystalUsing a synergistic strategy of a weak reductant and an anionic passivation layer,we have successfully obtained a silver cluster Ag89,characterized by a truncated tetrahedral geometry.This cluster consists of an isolated Ag13 core passivated by multiple AgS47-units and pNH2PhAsO32-ligands.It is noteworthy that this Ag13 icosahedron stands out as the most sizable separable subvalent silver core underneath the silver shell,characterized by a distinctly welldefined core-shell boundary so far.It serves as a precise embryonic model derived from the reduction of Ag+to Ag0,succeeded by the aggregation into large silver nanoparticles.DMF works in synergy with the anionic passivation layer to regulate the reduction kinetics,thereby enabling the capture of ultra-small subvalent silver cores.In addition,Ag89 exhibits excellent photothermal conversion performance with potential application in remote ignition.This research provides an innovative synthetic strategy to accurately capture and identify various subvalent silver cores in diverse systems and expands the application prospects of silver clusters.