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Synthesis,Separation And Characterization Of Erbium-containing Endohedral Metallofullerenes

Posted on:2020-11-08Degree:MasterType:Thesis
Country:ChinaCandidate:S F HuFull Text:PDF
GTID:2381330599459299Subject:Nanoscience and nanotechnology
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With the continuous development of science and technology,some carbon allotropes have been discovered,such as fullerenes,graphene,carbon nanotubes and so on.Among them,fullerenes are the only allotropes of carbon having a defined molecular structure,and are soluble in various organic solvents and have attracted widespread attention.Interestingly,the rich carbon cage is composed of the five-and six-membered ring system,so it gives a large amount of?electrons on its surface,giving it many special properties as well.In addition,some atoms,molecules,and clusters can be embedded inside the fullerene cage to form a unique molecule called“metallofullerene”.The clusters embedded in the fullerenes transfer charges to the corresponding cage,which in turn makes the cage obtain a novel charge distribution,which promotes its special physicochemical properties.At the same time,fullerene cages can provide a unique chemical environment for its internally embedded clusters,which in turn contributes to the research of different internal cluster systems.Although in the past 20 years,a series of analytical characterization methods such as HPLC,Mass spectra,UV-vis-NIR,NMR,TEM and DFT calculations,a series of studies on the structure and properties of metal fullerenes have been conducted in depth.However,some of the results were proved to be wrong by subsequent single crystal X-ray diffraction crystallography.As the most intuitive and reliable method for characterization of molecular structures,single crystal X-ray diffraction crystallography has been widely used and recognized.In this thesis,the crystal structure and electrochemical properties of a series of metal fullerenes have been systematically studied.The main research contents and results are summarized as follows:?1?Two Er@C82 isomers have been isolated and unambiguously characterized as Er@C2v?9?-C82 and Er@Cs?6?-C82,respectively,by single-crystal X-ray diffraction.Er@Cs?6?-C82 is identified as a dimeric structure in the crystalline state,but the dimerization does not occur for Er@C2v?9?-C82 under identical crystallization conditions,indicating a cage-symmetry-induced dimerization process.Density functional theory?DFT?calculations reveal that the major unpaired spin resides on a special carbon atom of Er@Cs?6?-C82 which leads to the regioselective dimerization.Calculations also found that the dimeric structure of Er@Cs?6?-C82·Ni?OEP?is much more stable than the two monomers,suggesting a thermodynamically favorable dimerization process.Vis-NIR spectrometric and electrochemical results demonstrate that the electronic structure of Er@C82 isomers is Er3+@C823-,instead of the theoretically proposed Er2+@C822-.?2?Successful isolation and unambiguous crystallographic assignment of a series of Er-based dimetallofullerenes present new insights into the molecular structures and metal-metal bond of endohedral metallofullerenes.These species are identified as Er2@Cs?6?-C82,Er2@C3v?8?-C82,Er2@C1?12?-C84,and Er2@C2v?9?-C86,and show that,though the Er positions are disordered inside the fullerene cage,the Er-Er bond distance is within the range of 3.24-3.76?.Moreover,theoretical studies rationalize that these Er2@C82-86 isomers prefer to transfer the two 6s electrons of each Er to the corresponding cages and remaining the 4f electrons to form the Er-Er bond.Interestingly,natural bond orbital analyses demonstrate that the two Er atoms in the three Er2@C822 and Er2@C86isomers form a two-electron-two-center Er-Er single bond,however,for Er2@C1?12?-C84with the longest Er-Er distance among title species,a single one-electron-two-center Er-Er bond is identified.Thus,it is proposed that the character of Er-Er bonding depends on the Er-Er distance,which is dictated by the cage type.Additionally,electrochemical studies suggest that Er2@C82-86 are a good electron donor instead of an electron acceptor.?3?A series of Er-based nitride clusterfullerenes,Er3N@C80-88,have been successfully synthesized and isolated.In particular,Er3N@Ih?7?-C80,Er3N@D5h?6?-C80,Er3N@C2v?9?-C82,Er3N@Cs?51365?-C84,and Er3N@D2?35?-C88 have been characterized by single-crystal X-ray diffraction for the first time.The planer configuration is identified for the inserted Er3N clusters,and the Er-N distance increases in accordance with the cage expansion to maintain strong metal-cage interactions.Additionally,their electrochemical properties are studied by cyclic voltammetry.It is found that the first reduction potentials are roughly similar,whereas the first oxidation potentials are cathodically shifted along with the increase of the cage size in Er3N@C2n?2n=80,84,86,88?isomers,leading to the decrease in the corresponding electrochemical band gap.Moreover,Er3N@C2v?9?-C82shows the smallest electrochemical band gap among the Er3N@C80-88 series,and its small first oxidation potential indicates good electron donating ability.
Keywords/Search Tags:Fullerenes, Crytal structure, Single crystal X-ray diffraction, Electrochemical, Erbium-containing endohedral metallofullerenes
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