Theoretical studies of C_(70)(OH)_n (n = 14, 16, 18 and 20) fullerenols

摘要

The experimental results indicated that polyhydroxylated C_(70) fullerence may generate water soluble C_(70)(OH)_n fullerenols with n = 14, 16, 18 and 20. The plausible reaction mechanism has been proposed with the consideration of cyclosulfation and hydrolysis. According to the experimental results, the number of hydroxyl substitutes in C_(70)(OH)_n fullerenols should be even. Random subroutine in MS FORTRAN 5.0 program library and reaction-mechanism consideration were first used to generate the structure of possible isomers for C_(70)(OH)_(14), C_(70)(OH)_(16), C_(70)(OH)_(18) and C_(70)(OH)_(20) fullerenols and reaction precursors C_(70)(SO_4)_7, C_(70)(SO_4)_8, C_(70)(SO_4)_9 and C_(70)(SO_4)_(10). The heats of formation, relative stability and optimized structures have been generated by semi-empirical PM3 calculation. Among the possible structures, the electronic structures of these having higher symmetry were then computed. According to the structure analysis, the relative stability of fullerenols depends on the number of hydroxy addends in the equatorial belt region. The 2D Schlegel diagrams of C_(70)(OH)_n fullerenols were presented for the geometrically optimized structure by PM3 calculations and contained exact positions of hydroxy addend in C_(70). These diagrams may be helpful in the investigation of the physical properties of starburst polymers or other groups substituted onto fullerenols. This theoretical computational procedure for searching possible isomers may be a helpful tool for isomer study with symmetry consideration.