Theortical Study On The Structures Of Endohedrally Hydrocarbon Molecule Doped C₆₀ And (5, 5) Single Walled Carbon Nanotube

Kroto et al discovered the Buckminster-fullerene in 1985 and Kraetschmer et al succeeded in producing macroscopic quantities of C₆₀ in 1990. In the next year, carbon nanotubes were discovered by S. Iijima. Then, the unique structure and properties of C60 and carbon nanotubes attracted considerable attention and lead people to the novel fields of materials. Since the first endohedral metallofullerenes, La@C₈₂ was discovered in 1991, there has been much interest in studying not only endohedral fullerene but also endohedral carbon nanotube which could be ideal container for some small molecules such as H₂, CH₄ and so on.In this paper, endohedrally acetylene, ethylene and ethane doped fullerene (C₂H₂@C₆0, C₂H₄@C₆0 and C₂H₆@C₆0) and single-walled carbon nanotube(C₂H₂@(5,5)SWNT, C₂H₄@(5,5)SWNT and C₂H₆@(5,5)SWNT) were studied theoretically using Density Functional Theory (DFT) at B3LYP leveal, respectively. The main results are as follow:1. When the dopant sited at the center of the C60 cage, the energy of complex is at its minimum. The dopant is an electron acceptor and the cage is a donor which is different from the case of metallofullerenes. The frontier orbital analysis and the binding energy calculations suggest that the formations of C₂H₂@C₆0, C₂H₄@C₆0 and C₂H₆@C₆0 would be endothermic. The cage and dopant affect each other rarely except for the slight distortion of C₆0 cage and compression of the hydrocarbon molecules. Apparently, C₆0 could be a good container for some small hydrocarbon molecules like C₂H₂, C₂H₄ and C₂H₆ theoretically. But it may be more practical experimentally if the cage would be higher fullerenes whose diameter are larger than 9(?) or use some special synthetic routes similar to opening a hole in the fullerene through chemical modification.2. The isomer in which the dopant is parallel to the wall of SWNT is more stable than that of normal to the wall. The calculations suggests that the formations of C₂H₂@(5,5)SWNT, C₂H₄@(5,5)SWNT and C₂H₆@(5,5)SWNT are endothermic; The frontier molecular orbital analysis shows that doping hydrocarbon molecule made the increasment of the HOMO-LUMO gap; the insertion of the hydrocarbon molecule in the center of the nanotube enlarge the diameter of the nanotube and the nanotube outside made the C-C and C-H bond lengths of hydrocarbon molecule compressed slightly and the bigger the dopant is, the tighter the compression is; a small quantity of electron transfer from (5,5)SWNT to the hydrocarbon molecule happenes and the amount of the electron transfer in the three compounds is the following sequence of C₂H₂@(5,5)SWNT2H₄@(5,5)SWNT2H₆@(5,5)SWNT.