Beyond metallo-carbohedrenes: growth and decomposition of metal-carbon nanocrystals

Abstract

The recently discovered family of metal-carbon clusters, designated metallo-carbohedrenes or [open quotes]met-cars[close quotes] by Castleman and co-workers, are reinvestigated with a focus on titanium and vanadium systems. In addition to the stable M[sub 8]C[sub 12][sup +] clusters reported previously, a family of larger metal-carbon systems are observed. Mass spectroscopy and mass-selected laser photodissociation measurements are used to investigate the structures and stabilities of these systems, which contain up to 60 atoms in the cluster framework. The larger metal-carbon species exhibit 1/1 M/C stoichiometries characteristics of cubic lattice structures and are therefore designated as [open quotes]nanocrystals[close quotes]. The species Ti[sub 14]C[sub 13][sup +] and V[sub 14]C[sub 13][sup +], which are proposed to have the 3 X 3 X 3 cubic structure, are especially abundant and are believed to have stabilities comparable to those of the M[sub 8]C[sub 12] species. Photodissociation of larger nanocrystals produces both the 8/12 and 14/13 stoichiometries as abundant photofragments. Evidence is also presented for the formation of endohedral met-car clusters containing a central carbon atom, which are formed as photodissociation products from larger systems. 37 refs., 5 figs., 1 tab.