Synthesis,Separation And Characterization Of Dysprosium-Containing Endohedral Metallofullerenes

Fullerene is a class of spherical molecule,composed of twelve five-membered rings and several six-membered rings.As the internal three-dimensional space allows metal atoms or metal clusters enclosed,a kind of special hybrid molecule is formed,named endohedral metallofullerene（EMF）.Different from empty fullerenes,EMFs have unique molecular structures and properties due to the charge transfer between metal atoms and the carbon cage,which arouse great interest of researchers.At present,although there have been a few reports on dysprosium-based（Dy-based）EMFs,the research on their macro-synthesis,structures and property characterization is still lacking.In this thesis,the preparation conditions of the DC arc discharge method were optimized firstly,and several Dy-based mono-EMFs and Dy-based di-EMFs were synthesized.Then pure samples of these EMFs were obtained through enrichment and separation.Finally,their molecular structures and properties were studied by various characterization methods.The main content could be divided into the following parts:（1）Dy-based EMFs were synthesized by DC arc discharge method.Using dysprosium oxide（Dy₂O₃）and graphite powder as raw materials,three conditions were changed to optimize the synthesis process,consisting of Dy/C molar ratio（1/12,1/8,1/5）,helium gas pressure（20 k Pa,30 k Pa）and current intensity（100 A,110 A）.Finally,it was determined that the best condition for synthesizing Dy-based EMFs should be Dy/C molar ratio 1/12,helium gas pressure 30 k Pa,and current intensity 100 A,and the content of EMFs could reach 77%of C₈₄ content.（2）Two Dy-based mono-EMFs,Dy@C_2v（9）-C₈₂ and Dy@C_2v（17）-C₈₄,were successfully synthesized and isolated.Their structures were studied by single-crystal XRD crystallography for the first time.It is worth mentioning that the structure of C_2v（17）-C₈₄ is discovered and studied for the first time.Further X-ray diffraction results show that,in Dy@C_2v（9）-C₈₂,the Dy atom is freely rotating in a plane which is biased to one side of the carbon cage.However,the Dy atom tends to rotate along the band of contiguous hexagons in Dy@C_2v（17）-C₈₄.This phenomenon indicates that changes in size and configuration of the carbon cage will affect the movement of the internal metal atom.Electrochemical studies show that,compared to Dy@C_2v（9）-C₈₂ and other reported C₈₄-cage mono-EMFs,Dy@C_2v（17）-C₈₄ exhibits a lower first oxidation potential（-0.09 V）,and a more negative first reduction potential（-1.22 V）,indicating this EMF is a good electron donor,and it has a stronger reduction stability at the same time.（3）Two Dy-based di-EMFs isomers,Dy₂C₈₄-I and Dy₂C₈₄-II,were successfully synthesized and isolated.The vis-NIR spectrum of Dy₂C₈₄-I is similar to that of the reported M₂C₂@C_s（6）-C₈₂（M=Er,Ti,Sc）,inferred that Dy₂C₈₄-I should be a carbide cluster EMF,Dy₂C₂@C_s（6）-C₈₂.And the vis-NIR spectrum of Dy₂C₈₄-II is similar to that of the reported Er₂@C₁（12）-C₈₄,inferred that Dy₂C₈₄-II should be a di-EMF,Dy₂@C₁（12）-C₈₄.Electrochemical results show that Dy₂C₈₄-I has one oxidation step and four reduction steps,which is very similar to the Er₂C₂@C_s（6）-C₈₂.At the same time,the lower first oxidation potential of Dy₂C₈₄-I（+0.13 V）indicates that it is a good electron donor.Dy₂C₈₄-II has two oxidation steps and five reduction steps,which is quite different from Dy₂C₈₄-I.Compared with Er₂@C₁（12）-C₈₄,the first reduction potential of Dy₂C₈₄-II is more positive（-0.77 V）,indicating that it is a better electron acceptor.