Kb. Shelimov et Mf. Jarrold, CARBON CLUSTERS CONTAINING 2 METAL ATOMS - STRUCTURES, GROWTH-MECHANISM, AND FULLERENE FORMATION, Journal of the American Chemical Society, 118(5), 1996, pp. 1139-1147
Gas phase ion mobility measurements have been used to probe the struct
ures and interconversion of La2Cn+ (n = 1-100) isomers. The smallest L
a2Cn+ clusters (n less than or equal to 10) appear to be planar rings.
However, planar mono- and bicyclic rings (the dominant isomers for, C
-n(+) and LaCn+, n less than or equal to 30, clusters) are not observe
d for the larger La2Cn+ species. Instead, isomers which appear to be t
hree-dimensional ring complexes dominate for unannealed La2Cn+ (n grea
ter than or equal to 17) clusters. The formation of these complexes is
probably driven by electrostatic forces. For n greater than or equal
to 30 the three-dimensional ring complexes isomerize into metallofulle
renes (and metal-containing graphite sheets for n = 30-37). The estima
ted activation energies for these isomerization processes are about 1
eV lower than those estimated for similar processes for planar C-n(+)
and LaCn+ rings. Metallofullerenes with two non-endohedral metal atoms
(for n = 28-29), one endohedral metal atom (for n = 31-100), and two
endohedral metal atoms (for n greater than or equal to 64, only even n
), are identified. Fullerene derivatives (presumably fullerene + ring
complexes) are abundant in the unannealed isomer distributions for La2
Cn+ (n greater than or equal to 50) clusters, but readily isomerize in
to regular fullerenes upon collisional heating.