Theoretical studies on the structures and stabilities of various possible isomers of C70O3

The equilibrium geometrical structures, relative stabilities and vibrationa l frequencies for the possible isomers of the fullerene derivatives C70O3 h ave been investigated using the semi-empirical methods AM1, PM3 and MNDO. T he 43 isomers of C70O3 have been studied on the basis of the most stable is omer of C70O2(1,2 and 5,6-epoxy [70] fullerene) The calculation results sho w that there are 38 epoxide-like structures and five annulene-like structur es. The epoxide-like structures are formed by oxygen atoms bridging across the unequatorial belt 6-6 bonds, while the annulene-like structures are for med with one oxygen atom bridging across the equatorial belt 6-6 bonds. Amo ng these epoxide-like structures, the isomer-l, with three oxygen atoms bri dging across the 6-6 bonds on the same six-membered ring closest to the pol e of C-70, is the most stable one. Among the annulene-like structures, the most energetically preferred structure is isomer-39, in which the three oxy gen atoms are positioned within the nearest neighboring six-membered rings. (C) 2000 Elsevier Science B.V. All rights reserved.