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.