Theoretical study of structure and stability of fullerene derivatives CO50X(X = SiHO2, PH, S)

The structure and stability of all possible isomers of C50X(X = SiH2, PH, S) were investigated by ab initio HF/3-21G calculations. The calculation results indicate that the preferred position for cycloaddition of SiH2, PH, and S on C50 is consistent, i.e. on the C3-C4 and C4-C4 sites of C50, and the resultant most stable cycloaddition isomers are [5,6]-closed and [5,5]-closed structures. The main driving force governing the stability of the C50X(X = SiH2, PH, S) isomers is the strain, or the conjugative effect, or the combination of strain and conjugative effect, depending on the addition positions and the types of the attacked C-C bonds. Further, the structures and stabilities of C50X(X = SiHO2, PH, S) are compared with those of the C50X(X = CH2, NH, O), and a general conclusion are drawn: the size of the attacking atom and the type of the attacked C-C bond are two decisive factors for the formation of open or closed structure of the C50X isomer.