Synthesis, Separation And Properties Of Fullerenes Embedded With Holmium Clusters

Endohedral fullerenes（EMFs）are composed of carbon cages and endohedral atoms（clusters）.The diversity of the structure of carbon cages and endohedral atoms（clusters）enriches the structure of EMFs and makes them have unique physical and chemical properties.EMFs have important applications in energy conversion,biomedicine and other fields.Endohedral metal cluster fullerenes are an important branch of EMFs.At present,there are a few studies on lanthanide holmium elements in cluster fullerenes.The study of endohedral holmium cluster fullerenes is expected to improve the abundance of EMFs and deepen the understanding of their structure and properties,especially the effect of the interaction between carbon cages and endohedral clusters on the structure of Ho-EMFs.The physical properties of EMFs will change with the changes of cluster structure.Therefore,the regulation of cluster structure is one of the most interesting topics in the field of fullerenes.Experiments show that the clusters of carbides and oxides are curled in small carbon cages and stretched in large carbon cages.The cluster structure can be changed by adjusting the size of carbon cages.In this paper,the synthesis,separation and properties of Ho₂O@C₂（13333）-C₇₄ and Ho₂O@D_2d（51591）-C₈₄ are described in detail,and the configuration of Ho₂O is analyzed in depth.At the same time,several isomers Ho₂@C₈₂,Ho₂O@C₈₂ and Ho₂C₂@C₈₂ are synthesized and separated,and their spectra,electrochemical and magnetic properties are characterized in detail.The research contents are as follows:（1）A novel oxide cluster fullerene Ho₂O@C₂（13333）-C₇₄4 was prepared and separated by DC arc discharge using Ho₂O₃ as metal donor and weak oxidizing CO₂ as oxidant.Single crystal X-ray diffraction（SC-XRD）studies show that Ho₂O clusters extend in small carbon cages of non-IPR C₂（13333）-C₇₄.The Ho-O-Ho angle is greater than 170°.The cluster structure is highly correlated with the shape of the carbon cage and the structure of the carbon cage.Density functional theory（DFT）shows that the electron transfer from the cluster to the carbon cage stabilizes C₂（13333）-C₇₄.The superconducting quantum interference device（SQUID）measurs that its paramagnetic magnetic moment is 9.8.?_B at2K,and its electrochemical properties are similar to that of Sc₂C₂@D_3h（14246）-C₇₄.（2）A novel oxide cluster fullerene Ho₂O@C₈₄ was synthesized for the first time.SC-XRD showed that its carbon cage structure is D_2d（51591）.The angle of Ho-O-Ho changes between 172.48°and 177.03°.The O atom is located on the crystal mirror plane,highly ordered,and Ho atom is highly disordered,mainly distributed at 10 sites.DFT showes that D_2d（51591）is more stable than C_2v（51575）and C₁（51383）,and that Ho-O transfers four electrons to C₈₄.（3）We synthesized a variety of fullerenes Ho-C₈₂,including Ho₂@C₈₂,Ho₂O@C₈₂and Ho₂C₂@C₈₂.Their carbon cage structures were characterized by spectroscopy as C_s,C_2v and C_3v.This work proves the existence and successful separation of Ho₂@C₈₂,Ho₂O@C₈₂ and Ho₂C₂@C₈₂,which have important influence on enriching the metal cluster fullerenes.