Research Of Ag₂₉ Nanocluster And Its Derivatives

Metal nanoclusters,also known as ultra-small metal nanoparticles,occupy the gap between discrete atoms and plasmonic nanomaterials,and are an emerging class of atomically precise nanomaterials.Their physical-chemical properties,such as luminescence,chirality,magnetism,catalysis,and electrochemistry,which can be rationalized in terms of their quantum size effect as well as discrete electronic states,are intriguing.Additionally,the atomically precise nature of their structures enables elucidation of structure-property relationships,which is essential if nanoclusters with enhanced performances are to be rationally designed.Metal nanocluster is a type of templated nanomaterial?nanoclusters with different templates displayed distinct physicochemical properties;however,for nanoclusters with a specific template,their structures and properties can be precisely controlled,and the obtained structure-property correlations can be exploited in other cluster templates.Previously,Au₂₅ and Ag₄₄ serve as the most familiar cluster research template.However,their unsatisfied optical properties and stability strict their potential applications.In this context,nanocluster researches would like to develop a new nanocluster research template.In this dissertation,a new cluster research model in the nanocluster family has been developed?the Ag₂₉ nanocluster.The researches in this dissertation include the controllable preparations,structural determinations,and property investigations of Ag₂₉ relevant nanoclusters,which have led to numerous conceptual and practical developments in the nanocluster science.Based on the Ag₂₉ nanocluster template,we study the structure control,the self-assembly phenomenon,the structure-property correlations,and potential applications of Ag₂₉ and its correlated nanoclusters.The chemistry of Ag₂₉ nanoclusters has provided an extensive class of nanomaterials with controllable compositions/configurations and tunable functionalities,based on which several principles have been fully established and worked favorably for guiding the preparation of new nanocluster materials.The main contents are divided into the following four parts:1.Controllable preparation,structure control,sturtcure-property correlations of M₂₉?S-Adm?₁₈?PPh₃?₄ nanoclusters??1?The synthesis and X-ray crystal structure of Pt₁Ag₂₈?S-Adm?₁₈?PPh₃?₄ nanocluster with a tetrahedral shape were presented.The Pt₁Ag₂₈ was synthesized by reacting Pt₁Ag₂₄?SPh Me₂?₁₈simultaneously with Adm-SH and PPh₃ ligands.A tetrahedral structure is found in the metal framework of the Pt₁Ag₂₈ nanocluster and the overall surface shell(Ag₁₆S₁₈P₄),as well as the discrete Ag₄S₆P₁ motifs.The Pt₁Ag₁₂ kernel adopts a face-centered cubic?FCC?arrangement,which is observed for the first time in alloy nanoclusters in contrast to the commonly observed icosahedral structure.The Pt₁Ag₂₈ nanocluster exhibits largely enhanced photoluminescence?quantum yield QY=4.9%,emission centered at?672 nm?while the starting material(Pt₁Ag₂₄nanocluster)is only weakly luminescent?QY=0.1%?.Insights into the nearly 50-fold enhancement of luminescence are obtained by analysis of ultrafast electronic dynamics.This study demonstrates atomic-level tailoring of the alloy nanocluster properties by controlling the structure.?2?A nanosystem based on the M₂₉?S-Adm?₁₈?PPh₃?₄?where,S-Adm is the adamantane mercaptan,and M is Ag/Cu/Au/Pt/Pd?has been established,which leads to the atomically precise operation on each site in this M₂₉ template.Specifically,a library of 21 species of nanoclusters ranging from mono-metallic to tetra-metallic constitutions has been successfully prepared step by step with in-situ synthesis,target metal-exchange and forced metal-exchange methods.More importantly,owing to the mono-dispersity of each nanocluster in this M₂₉ library,the synergetic effects on the optical properties and stability have been mapped out.This nanocluster methodology not only provides new fundamental principles to produce alloy nanoclusters with multi-metallic compositions and mono-dispersed dopants,but also provides an intriguing nano-model that enables us to grasp the intermetallic synergy at the atomic level.?3?A reversible transformation between the face-centered cubic?FCC?and icosahedral isomers of the Pt₁Ag₂₈ nanoclusters accomplished in the ligand-exchange processes was presented.Ligand-exchange of the 1-adamantanethiolate protected Pt₁Ag₂₈ by cyclohexanethiolate could transform the FCC kernel to the icosahedral isomer.Interestingly,the icosahedral Pt₁Ag₂₈ could be reversibly transformed to the FCC configuration when the cyclohexanethiolate ligand is replaced again by 1-adamantanethiolate.A combination of UV-vis absorption,mass spectrometry,photo-luminescence and X-ray absorption fine structure unambiguously identifies that the FCC-to-icosahedral structure transformation of Pt₁Ag₂₈ involves two distinct stages:?i?ligand-exchange induced outmost motif transformation,and?ii?abrupt innermost kernel transformation.As a result of this structural transformation,the emission wavelength of the Pt₁Ag₂₈ red-shifts from 672 to720 nm,and the HOMO-LUMO energy gap reduces from 1.86 to 1.74 e V.This work presents the first example of nanocluster isomers with inter-switching configurations,and will open up new insights in manipulating the properties of nanoclusters through controllably tuning their structures.?4?On the basis of the M₂₉?SR?₁₈?PR'₃?₄ cluster system,the control over the vertex phosphine ligands is accomplished.Therefore,a combination of the manipulation of vertex phosphines in this work and of internal metals and surface thiols reported previously realizes the control over the M₂₉?SR?₁₈?PR'₃?₄ cluster template.The principles for regulating the photo-luminescence?PL?of M₂₉ clusters via dictating their metal compositions,surface thiols,and vertex phosphines are exploited to rationally design the most emissive nanocluster among the M₂₉ cluster family.Overall,this work fills the missing part for the manipulation of M₂₉?SR?₁₈?PR'₃?₄ nanoclusters,providing an ideal nanomodel that enables us to grasp the structure-property correlations at the atomic level.2.Structure evolutions based on the Pt₁Ag₂₈?S-Adm?₁₈?PPh₃?₄ nanocluster??1?The concept of“graft-onto”has been exploited to render the Pt₁Ag₂₈?S-Adm?₁₈?PPh₃?₄nanocluster growth on surface structures.Specifically,the Ag₂?DPPM?Cl₂ complex is used for re-constructing the surface structure of Pt₁Ag₂₈?SR?₁₈?PPh₃?₄(Pt₁Ag₂₈,SR=1-adamantanethiolate)and producing a size-growth nanocluster?Pt₁Ag₃₁?SR?₁₆?DPPM?₃Cl₃(Pt₁Ag₃₁).The grafting effect of Ag₂?DPPM?Cl₂ induces both directly changes on the surface structure?e.g.,size growth,structure transformation,and surface rotation?and indirectly changes on the kernel structure?from a fcc configuration to an icosahedral configuration?.Two opposite types of Pt₁Ag₃₁ enantiomers are observed in the crystal lattice,and are self-assembled with a layer-by-layer A?R-enantiomer?#B?L-enantiomer?#A?R-enantiomer?#B?L-enantiomer?packing mode.Remarkable differences have been observed by comparing optical properties between Pt₁Ag₂₈ and Pt₁Ag₃₁.Significantly,Pt₁Ag₃₁ exhibits high photo-luminescent intensity with a quantum yield of 29.3%,which is six times that of the Pt₁Ag₂₈.Overall,this work presents a new approach?i.e.,graft-onto?for the precise dictating of nanocluster surface structures at the atomic level.?2?The valence self-regulation of sulfur from the“-2”valence state in thiols to the“-1”valence state in hydroxylated thiolates has been accomplished using the Pt₁Ag₂₈ nanocluster as a platform–the first time that the“-1”valent sulfur has been detected as S^-1.Two novel nanoclusters,Pt₁Ag₂₈?SR?₂₀ and Pt₁Ag₂₈?SR?₁₈?HO-SR?₂?where SR represents 2-adamantanethiol?,have been synthesized and characterized–in the latter nanocluster,the presence of hydroxyl induces the valence regulation of two special S atoms from“-2”?in SR?to“-1”valence state in the HO-S?Ag?R.Due to the contrasting nature of the capping ligands in these two nanoclusters(i.e.,only SR in Pt₁Ag₂₈?SR?₂₀ or both SR-and HO-SR-in Pt₁Ag₂₈?SR?₁₈?HO-SR?₂),they exhibit differing shell architectures,even though their cores(Pt₁Ag₁₂)are in the same icosahedral configuration.Single crystal X-ray diffraction analysis revealed their 1:1 co-crystallization,and mass spectrometry verified the presence of hydroxyls on Pt₁Ag₂₈?SR?₁₈?HO-SR?₂.3.Property investigations and structure evolutions based on the Ag₂₉?SSR?₁₂?PPh₃?₄nanocluster??1?A novel mechanism involving the restriction of“dissociation-aggregation pattern”of ligands is presented using Ag₂₉?SSR?₁₂?PPh₃?₄ nanocluster as a model.Accompanied by the addition of PPh₃ into a DMF solution of Ag₂₉?SSR?₁₂?PPh₃?₄,the PL intensity of Ag₂₉?SSR?₁₂?PPh₃?₄ could be significantly enhanced?13 times,quantum yield from 0.9%to 11.7%?due to the restricted PPh₃ dissociation-aggregation process.This novel mechanism is further validated by the low-temperature PL study.Different from the significant PL enhancement of the Ag₂₉?SSR?₁₂?PPh₃?₄,the non-dissociative Pt₁Ag₂₈?S-Adm?₁₈?PPh₃?₄ exhibits a maintained PL intensity under the same PPh₃-addition condition.Overall,this work presents a new mechanism for largely enhancing the PL of nanoclusters via modulating the dissociation of ligands on the nanoclustersurface,which is totally different from the previously repoted AIE phenomena in the nanocluster field.?2?A strategy of free valence electron centralization has been exploited to render parent Ag nanoclusters highly stable.The stability of Ag₂₉?SSR?₁₂?PPh₃?₄ has been controllably enhanced by stepwisely alloying the Ag₂₉ nanocluster to Ag₁₇Cu₁₂?SSR?₁₂?PPh₃?₄ and Au₁Ag₁₆Cu₁₂?SSR?₁₂?PPh₃?₄.Specifically,the tri-metallic Au₁Ag₁₆Cu₁₂ is ultra-stable even at 175^oC which is close to the nanocluster decomposition temperature.The structures of Ag₁₇Cu₁₂ and Au₁Ag₁₆Cu₁₂ nanoclusters are determined by SC-XRD.Furthermore,a combination of XPS measurements and DFT calculations demonstrates that the enhanced stability is induced by the centralization of the free valence electrons to the interior of the nanocluster.More importantly,the Au₁Ag₁₆Cu₁₂ enables the multi-component A³ coupling reaction at high temperatures,which remarkably shortens the catalytic reaction time from?5 hours to 3 minutes.Overall,this work presents a strategy for enhancing the thermal stability of nanoclusters via centralizing the free valence electrons to the nanocluster kernels.4.Self-assembly and applications based on the Ag₂₉?SSR?₁₂?PPh₃?₄ nanocluster??1?The first X-ray crystal structure of a Cs⁺-captured nanocluster,formulated as Cs₃Ag₂₉?SSR?₁₂?DMF?_x?x=5,6?,was presented.The capture of Cs⁺with Ag₂₉?SSR?₁₂?PPh₃?₄peels the PPh₃ ligands off from the nanocluster surface,giving rise to the Cs₃Ag₂₉?SSR?₁₂?DMF?_x.The Cs⁺-cluster interactions not only alter the geometric structure of the Ag₂₉?SSR?₁₂ kernel,but also assemble Ag₂₉?SSR?₁₂ clusters into one-dimension,cluster-based lines.Remarkable differences have been observed by comparing the optical properties of the Cs₃Ag₂₉?SSR?₁₂?DMF?_xnanocluster in solution or in crystallized films.Overall,this work is of great significance for revealing both the Cs⁺-induced intra-cluster transformation of nanocluster structures,and the Cs⁺-induced inter-cluster self-assembly.?2?The hierarchical self-assembly of atomically precise Ag₂₉?SSR?₁₂?PPh₃?₄ nanoclusters into micrometric linear chains?1D array?,grid networks?2D array?,and superstructures?3D array?was presented.In the crystal lattice,the Ag₂₉?SSR?₁₂?PPh₃?₄ nanoclusters can be viewed as unassembled cluster dots(Ag₂₉-0D).In the presence of Cs⁺cations,the Ag₂₉?SSR?₁₂ nano-building blocks are selectively assembled into distinct arrays with different oxygen-carrying solvent molecules?Cs@Ag₂₉?SSR?₁₂?DMF?_x as 1D linear chains(Ag₂₉-1D),Cs@Ag₂₉?SSR?₁₂?NMP?_xas 2D grid networks(Ag₂₉-2D),and Cs@Ag₂₉?SSR?₁₂?TMS?_x as 3D superstructures(Ag₂₉-3D).Such a hierarchical self-assembly of these Ag₂₉?SSR?₁₂ units has not only been observed in their crystalline state,but also in their amorphous state.Due to the diverse surface structures and crystalline packing modes,these Ag₂₉-based assemblies manifest distinguishable optical absorptions and emissions in both solutions and crystallized films.Furthermore,the surface areas of the nanocluster crystals are evaluated,the maximum value of which occurs when the cluster nano-building blocks are assembled into 2D arrays(i.e.,Ag₂₉-2D).Overall,this work presents an exciting example of the hierarchical assembly of atomically precise nanoclusters by simply controlling the adsorbed molecules on the cluster surface.?3?A versatile strategy to render hydrophobic nanoclusters water-soluble?the micellization of nanoclusters in the presence of solvent-conjoined Na⁺cations?which overcomes the above major challenge,was presented.Specifically,although the[Ag₂₉?SSR?₁₂?PPh₃?₄]^3-nanoclusters are absolutely hydrophobic,they show good dissolvability in the aqueous solution in the presence of solvent-conjoined Na⁺cations(Na₁?NMP?₅ or Na₃?DMF?₁₂).Such cations act as both counterions of these nanoclusters and surface cosolvent of cluster-based micelles in the aqueous phase.A combination of DLS?dynamic light scattering?and aberration-corrected HAADF-STEM?high angle annular dark field detector scanning transmission electron microscope?measurements unambiguously identifies that the phase-transfer of hydrophobic Ag₂₉ into water is triggered by the micellization of nanoclusters.Owing to the excellent water solubility and stability of[Ag₂₉?SSR?₁₂?PPh₃?₄]^3-[Na₁?NMP?₅]₃⁺in H₂O,its performance in cell-labelling has been evaluated.Furthermore,the general applicability of the micellization strategy has been verified.Overall,this work presents a convenient and efficient approach for the preparation of cluster-based,biocompatible nanomaterials.