Synthesis,Isolation And Characterization Of Thorium Based Endohedral Actinide Fullerenes

Endohedral metallofullerenes（EMFs）feature both variable size and isomeric carbon cages which result in their tunable electronic and magnetic properties.In recent years,these compounds have ementrated great potential on the application in biomedicine,organic photovoltaic devices and other fields.The study of EMFs started with monometallofullenenes and have been expanded to dimetallofullerenens,trimetallofullerenes and cluster fullerenes etc.Most of these reported EMFs are lanthanide based.While most of the reported lanthanide metal encapsulated inside the corresponding EMFs have formal oxidation state of +3,uranium has much richer valance states including +2,+3,+5 and +6.Thus,it is reasonable to speculate that the actinide EMFs would present very different electronic structure and physiochemical properties.However,up to now,the studies of actinide based EMFs are largely limited to theoretical calculation.The experimental study of these compounds remain largely unexplored,except for some mass peaks observed in mass spectrometry and the spectroscopic studies of U@C82 and Th@C84.Therefore,in this dissertation,we reported the synthesis,isolation and characterization of a series of novel Th-based EMFs for the first time and carried out the following works:（1）We have synthesized Th@C_2n（n=37-48）family by a modified arc discharge method,in which graphite rods packed with Th O2 and graphite powder were vaporized in the arcing chamber under a He atmosphere.In the resulting fullerene mixture,the most abundant species was found to be Th@C82,followed by Th@C86 and Th@C76.Furthermore,for the first time,we report the single crystal structure and full characterization of an actinide endohedral fullerene,Th@C82,which exhibits remarkably different electronic and spectroscopic properties compared to those of lanthanide EMFs.Single crystal X-ray crystallography unambiguously established the molecular structure as Th@C_3v（8）-C₈₂.Combined experimental and theoretical studies reveal that Th@C_3v（8）-C₈₂ is the first example of an isolated monometallofullerene with four electrons transferred from themetal to the cage,with a surprisingly large electrochemical band gap.Moreover,Th@C_3v（8）-C₈₂ displays a strong vibrationally coupled photoluminescence signal in the visible region,an extremely rare feature for both fullerenes and thorium compounds.（2）We have isolated a series of actinide based monometallofullerenes,including Th@C₈₀,two isomers of Th@C82（Th@C82（Ⅱ）,Th@C82（Ⅲ））,Th@C84 and two isomers of Th@C86（Th@C86（（40））,Th@C86（Ⅱ））.The UV-vis-NIR absorption spectra of these samples indicate that the cage of Th@C82（Ⅲ）and Th@C86（Ⅱ）are Cs（6）-C82 and C2v（9）-C86 respectively,while Th@C₈₀ and Th@C84 might have a new cage structure.The photoluminescence spectra show that the emission peaks of Th@C_2n（2n=80,82,86）have not been significantly affected by the size of carbon cage.Moreover,emission peaks of Th@C₈₀ shows the highest intensity among these Th based EMFs,which is consistent with the fact that no obvious absorption peak was observed in its UV absorption.（3）For the first time,the macroscopic actinide based dimetallofullerenes product,Th₂@C₈₀,has been successfully synthesized and isolated,and characterized by UV-vis-NIR absorption spectroscopy.The UV-vis-NIR absorption features of Th₂@C₈₀ are similar to those of Ih-C₈₀ based EMFs,such as La2@Ih-C₈₀.This suggests that the Th₂ likely transfer 6 electron to Ih-C₈₀ cage and the encapsulated Th ion takes an oxidation state of +3.Th₂@C₈₀ might be the first reported compounds which contains stable Th³⁺.