Theoretical and experimental study of fullerenol molecules and ions C60(OH)24 − n (OL) n and C60(OH)24 − n (OL) n L+ successively substituted by Alkali Metal atoms L (n = 1−24)

Abstract

The equilibrium geometric parameters and the energetic characteristics of fullerenol molecules and ions C60(OH)24 − n (OL) n and C60(OH)24 − n (OL) n L+ successively substituted by alkali metal atoms L with the number of substitutions n = 1–24 have been calculated by the density functional theory B3LYP/6-31G* method. For all compounds, the structure of the covalent [C60O24] cage in which the oxygen atoms are bound to the C atoms of the six-membered [C6] rings of the fullerene cage, six O atoms per [C6] ring. The lithium derivatives have been considered in most detail. Computations have shown that the first four single substitutions of Li for H in the OH groups attached to the same C6 ring require very low energy inputs, no more than 1 kcal/mol, and can spontaneously occur under common conditions. The further fifth and sixth single substitutions in the same C6 ring are endothermic, but the required energy inputs are also modest (on the order of few kcal/mol). The first and second cooperative substitutions of Li for H simultaneously in all four hydroxylated C6 rings require energy inputs of ∼3 and 11.6 kcal/mol, respectively; in the third and fourth fourfold substitutions, the energies increase by ∼15–16 kcal/mol. The mean partial energy per single substitution of Li for H in this series (n = 1−6) is ∼2 kcal/mol. Calculations have predicted that all C60(OH)24 − n (OLi) n molecules with intermediated degrees of substitution (n = 1−16) can be obtained under the conditions of relatively low energy inputs (for example, under the conditions of the MALDI experiment) and can exist in the isolated state. For the sodium- and potassium-substituted analogues, the qualitative pattern persists, but the H/Na and H/K substitutions are somewhat more endothermic. The computational results are compared with the MALDI mass spectrum of the [C60(OH) x (ONa) y -CH3COONa) system.