Syntheses,Structures And Properties Of Silver Clusters Protected By Organic Ligands

Significant metalophilic effect among metal ions in the coin group(gold,silver and copper),facilitates the aggregation of coin-metal ions to form metal-rich cluster structures.But the synthesis of silver clusters is hindered due to its poor stability.By ligating with ligands such as alkyne,pyridine,phosphine,thiol,etc.,the monodispersity and structural stability of silver clusters have been greatly improved,which provides possibility to cultivate single-crystal samples and determine its atomically precise structure.This thesis mainly discusses the design,synthesis and characterization of novel silver cluster compounds based on the three aspects of silver cluster-based outer ligand,inner core structure and electronic structure.In addition,we also introduce the use of silver-ligand interaction to achieve controllable synthesis of Ag@Carbon catalyst and applied to the oxygen reduction reaction.(1)Ten silver-thiolate compounds were synthesized by solution self-assembly method dictating by different rigid pyridyl ligands,and their precise composition was determined by single crystal X-ray diffraction.Furthermore,we systematically studied the influence of different pyridyl ligands on the structure of silver-thiolate compounds.In addition,by analysing the Ag-S bond lengths in silver-thiolate compounds,it is found that the silver ions connected to pyridine tend to have longer Ag-S bond lengths.This research provides inspiration and guidance for the structure design and synthesis of silver-thiolate compounds.Moreover,we used zwitterionic ethynide ligands as surface protection ligands for silver clusters for the first time.Under different reaction conditions,we obtained a series of zwitterionic ethynide ligands protected silver ethynide compounds.These clusters showed an interesting positive charge protection layer,and further connecting by ^tBu PO₃^2-ligand,a rare 80-nuclei silver ethynide cluster was formed.The experimental results prove that the choice of surface protection ligand is very important for the design and synthesis of silver cluster with novel structure.(2)The thiol ligand slowly released the S^2-template to guide the synthesis of nine novel silver-thiolate clusters and the relationship between the structure and its fluorescence properties was studied.First,we compared similar clusters of Ag₁₁ and S@Ag₁₅,which revealed that the insertion of S^2-template greatly changed the electronic structure of silver-thiolate clusters and led to a 56 nm redshift in the fluorescence wavelength.In addition,S^2-ions can also form Ag₃S₃ templates in situ with silver ions,and further cooperated with other inorganic anion templates to guide the formation of nest-like clusters.We found that with the change of the anion template,the solid-state fluorescence wavelength of the nest-like Ag₃₃ also shifted accordingly.Through the adjustment of the solvent,S^2-ions and silver ions formed a larger silver sulfide template,and self-assembled to form high-nuclearity silver-thiolate clusters Ag₅₆ and Ag₅₈,and their structure and fluorescence properties were studied.This work reveals that the core template has a significant influence on the structure and properties of the silver clusters.(3)Two novel Ag₆₂ nanoclusters were synthesized by solvothermal method and their fluorescence properties were discussed.Sodium borohydride was reacted with silver-thiolate polymer precursor and CF₃SO₃Ag in methanol,and the resulting solution undergone a solvothermal reaction to form[Ag₆₂S₁₂(^tBu S)₃₂]⁴⁺containing two free electrons.When replacing CF₃SO₃Ag with(CF₃SO₃)₂Cu,a similar cluster[Ag₆₂S₁₂(^tBu S)₃₂]²⁺with 4 electrons was obtained.The 4-electron Ag₆₂ has no room temperature fluorescence properties,while the two-electron Ag₆₂ emits 615 nm fluorescence under the excitation of 555 nm light.This work confirms that the electronic structure of silver nanoclusters has a decisive influence on their fluorescence properties.(4)By adjusting the self-assembly process of silica precursor and polymer monomer through the interaction of Ag⁺-ligand,we have rarely obtained porous tubular silica and carbon nanomaterials in the St(?)ber system.Using tetraethyl orthosilicate(TEOS)and resorcinol/formaldehyde(RF),induced by Ag⁺and pyridyl surfactants,a porous carbon tube(RF1)with a high surface area was generated.In addition,when tetrapropyl orthosilicate(TPOS),which has a slower hydrolysis rate than TEOS,was used,carbon tubes(RF2)with better uniformity were produced.In addition,when dopamine hydrochloride was used instead of RF as the carbon precursor,tubular polydopamine(TDA)with a length of tens of microns can be obtained.Due to its unique structural characteristics,high surface area,metallic silver doping and nitrogen-rich content,TDA had excellent catalytic activity for oxygen reduction reaction in alkaline solution.This work provides inspiration for the engineering design of micellar soft templates and the extension of the St(?)ber method to synthesize novel nanostructures.