Systematic investigation of the molecular behavior of C50X2(X = H,F): An echo of the H/F parallels on structures and energetics among their derivatives

Abstract

A systematic investigation of all possible C50H2 and C50F2 isomers has been performed using the semiempirical methods AM1 and PM3. The equilibrium geometrical structures, heats of formation, HOMO–LUMO energy gaps, ionization potentials, electronic affinities, strain and aromaticity have been studied. The results indicate that isomer-78, which corresponds to 1,4-addition in the six-membered ring located on the equator, is the most stable isomer for both C50H2 and C50F2. The driving force governing the stabilities of the presently studied C50X2 (X=H,F) isomers is the strain inherent in the C50 cage. The contribution of the conjugation effect to the stabilization is not able to compete with that of the strain. The relatively more stable C50X2 isomers have larger ionization potentials and smaller electronic affinities than C50, which suggests that it is more difficult to oxidize and reduce C50X2, i.e., the redox characteristics of C50 are weakened by hydrogenation and fluorination. The vibrational spectra and electronic absorption spectra of the hydrogenated and fluorinated fullerenes have been calculated, which could serve as a framework to interpret future experimental results. The computed nucleus independent chemical shifts (NICS) values also provide a basis for the possible characterization of these C50X2 isomers. Isostructural C50H2 and C50F2 molecules are predicted to have a constant energy difference. The phenomenon of H/F parallels on structures and energetics among derivatives of some fullerenes has been echoed.