Formation, Structure, and Stabilities of Metallocarbohedrenes

Time-of-flight mass spectrometric investigations of the formation of metallocarbohedrenes and binary metal metallocarbohedrenes under both direct laser vaporization and laser vaporization/molecular beam conditions were conducted. A wide range of Ti-to-carbon ratios and in other experiments a range of Ti-to-Zr molar ratios were explored. These new studies provide further insight into the formation process of Met-Car clusters and, moreover, serve to eliminate certain suggested formation mechanisms such as one involving the attachment of metal atoms to a preexisting core consisting of a 12-atom carbon cage. There is no evidence in the experiments to suggest that Met-Cars produced via direct laser vaporization exist in a higher energy configuration than those formed in a laser plasma and then subjected to cooling in a molecular beam expansion. Mass spectral distributions of binary metal metallocarbohedrenes produced under widely varying conditions provide evidence that there is one set of equivalent metal sites in the structures produced under both low- and high-energy conditions. Finally, the stability and bonding of metallocarbohedrenes are interpreted in terms of known chemistry for early transition metals.