Synthesis Of Endohedral Metallofullerenes And First-Principles Study Of Host-Guest System

Endohedral metallofullerenes(EMFs)are novel structures formed by encapsulating metal atoms or clusters into empty fullerene cages In the research of metallofullerenes,it is of certain significance to explore the synthesis of metallofullerenes with specific functions,and then to find the application of these molecular materials.Isotope-labeled fullerene molecules have specific functions and have applications in various fields such as substance transformation,biomedicine,analysis and testing,and energy metabolism,but their number and types are few and need further research.In addition,as a unique class of guest molecules,metallofullerenes can form host-guest systems with a variety of host molecules:such as carbon nanotubes,MOF,COF,etc.These host molecules expand the application scope of fullerenes,while the introduction of guest molecules can also regulate the properties of the host molecules,which can be applied to separation,spin regulation,molecular devices,etc.In this paper,isotope-labeled Sc315N@C80 and Sc315N@C78 with specific functions were synthesized based on the DC-arc-discharge method,and then first-principles calculations were used to explore the effect of intercalating different fullerene into COF-1 and COF-5 on the geometric structure and properties of the host molecules.The main contents are as follows:(1)Using 15N-labeled NH4Cl as solid nitrogen source,isotope-labeled scandium-based nitride endofullerenes,namely Sc315N@C80 and SC315N@C78,were synthesized based on DC arc discharge method.The presence of 15N in both was confirmed by mass spectrometry and further verified using Y3N@C80 as an internal standard.The prepared 15N-labeled metal nitride clusterfullerenes contain more than 98%of the 15N isotope.UV-Vis absorption spectroscopy and 13C NMR characterized Sc315N@C80 with Ih-C80 carbon cages.In this study,15NH4Cl was selected as an inorganic solid nitrogen source,and 15N-labeled Sc315N@C80 and SC315N@C78 were synthesized,indicating that 15NH4Cl can be rapidly decomposed during arc discharge,and the generated N atoms will participate in the assembly process of metallofullerenes.This study shows that 15NH4Cl as a nitrogen source can also be used to synthesize other kinds of metal nitride endometrial fullerenes.Therefore,15NH4Cl has universality as a solid nitrogen source.The prepared 15N isotope-labeled metal nitride endofullerene will expand the application of metallofullerene materials in isotope tracing and other fields.(2)We systematically calculated the geometric structures and binding energies of fullerene?COFs.The results show that the difference between the calculated and experimental values of the lattice parameters of fullerene?COFs is negligible.In addition,after C80/Sc3N@C80/Sc3C2@C80 is embedded in the pores of COF-1,the COF-1 monolayer will deform,so the interaction of these three molecules with COF-1 is stronger.After encapsulating different fullerenes,the COF-5 monolayers do not bend and still maintain a planar configuration,so the fullerene molecule has little influence on the geometric structure of COF-5.Compared with the fullerene?COF-1,the binding energy of the fullerene?COF-5 is more negative,indicating that the five guest molecules C60/C70/C80,S3N@C80 and Sc3C2@C80 are more likely to be incorporated in COF-5.This may be due to the larger pore size(27 ?)of COF-5,which makes it easier for guest molecules to intercalate.In the fullerene?COF-1,the binding energy of the C80/Sc3N@C80/Sc3C2@C80?COF-1 is more negative,so the interaction between the three fullerenes and COF-1 is stronger,which also indicates that the COF-1 with smaller pore size(15 A)is selective for the intercalation of fullerenes of different sizes.(3)We systematically calculated the electronic properties of COFs、fullerene?COFs.The results show that intrinsic COF-1 and COF-5 are both semiconductors.Comparing the TDOS and PDOS of COF-1,it can be seen that the VBM is mainly occupied by the 2pz state electrons of C;the CBM is mainly dominated by the 2pz state electrons of B.The VBM and CBM electrons of COF-5 are both provided by the 2pz state electrons of C.Compared with the pristine COFs,C60/C70/C80?COFs,Sc3N@C80?COFs,Sc3C2@C80?COFs exhibit semiconducting,semiconducting,and metallic properties,respectively.Consequently,the encapsulation of Sc3C2@C80 can change the properties of fullerene?COFs from semiconducting to metallic.The introduction of the paramagnetic metallofullerene Sc3C2@C80 makes the Fermi level of the host-guest system moves into valence band,and Sc3C2@C80?COFs exhibits metallicity and have a magnetic moment.Therefore,the electronic properties of COFs can be regulated by introducing Sc3C2@C80,which will prepare for the development of spintronic devices and guide the subsequent experimental design of covalent organic framework materials with different magnetic and electronic properties,extending Scope of application of metallofullerenes.