title: Theoretical insight for the metal insertion pathway of endohedral alkali metal fullerenes.
abstract: We have investigated the mechanism of alkali metal incorporation into C60 fullerene by density functional theory (DFT) at the UB3LYP/6-31G* level of theory. Calculations were performed to study the insertion pathways of Li(+), Na(+), and K(+) through six- or five-membered rings of fullerene, and the computed energy barriers of metal ion insertion are compared with the available experimental data. Between the two possible insertion pathways, metal ion insertion through [2 + 2 + 2] ring opening of the six-membered ring is found to be more favored than the insertion through the ring opening of the five-membered ring. The size of the ring openings generated by the three metal ions is likely to be correlated with their ionic size, which shows the smallest opening for Li(+) and the largest for K(+) cation. The insertion energy barriers of the ions are found to be increased in the order of Li(+) < Na(+) < K(+) in line with the experimental results. The ring opening made by breaking of C-C bonds during the metal ion insertion in six- or five-membered rings can cause the ring to be rearranged and convert back into a closed fullerene cage to form a stable endohedral metal-fullerene complex.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
authors.forename: Hema
authors.initials: H
authors.lastname: Malani
authors.forename: Dawei
authors.initials: D
authors.lastname: Zhang