Clusters, metal carbide

Metal-carbide clusters are relevant to the fonnation of both endohedral fullerenes and carbon nanotubes [1351. There also exists a class of apparently stable metal-carbide cluster ions, = Ti, V, Cr, Zr and Hf), called... 

Duncan M A 1997 Synthesis and characterization of metal-carbide clusters in the gas phase J. duster Soi. 8 239... 

Metal carbide clusters. M. Tachikawa and E. L. Muetterties, Prog. Inorg. Chem., 1981,28,203-238 (69). 

Niobium and rhodium cluster anions have been prepared by laser vaporization and the reactions with benzene studied by FT-ICR/MS (58). The reactions of the anions and similar cations have been compared. With few exceptions the predominant reaction of the niobium cluster anions and cations was the total dehydrogenation of benzene to form the metal carbide cluster, [Nb C6]-. The Nb19 species, both anion and cation, reacted with benzene to form the coordinated species Nb 9C6I I6p as the predominant product ion. The Nb22 ions also formed some of the addition complex but the Nb2o Nb2i, and all the other higher clusters, formed the carbide ions, Nb C6. ... 

Tachikawa, Mamoru and Muetterties, E. L., Metal Carbide Clusters. 28 203... 

Cluster modeling of possible chemisorption states and of possible intermediate states in surface reactions can to a first approximation be useful in guiding experiments or interpretations of experimental data for surface reactions (23-25). One important and enlightening result (6, 26, 27) in metal carbide cluster chemistry will be used here to illustrate this particular point because it bears directly on the importance of multicenter C-H-M bonding for hydrocarbon fragments in metal chemistry. 

Fullerenes with metal clusters inside - cluster metallofullerenes. To date, only metal nitride and metal carbide clusters were found within fullerene cages, with one recent example of a metal oxide cluster, that is, SC4O2 Cso [31], but they constitute a large percentage of isolated EMFs. 

A review of metal carbide clusters, including their syntheses is available . 

This strategy is exploited to synthesize numerous mixed-metal carbide clusters by using one of the techniques mentioned earlier to build up a larger mixed-metal cluster from a smaller one and then oxidatively degrading this product to cause metal exchange ... 

Figure 4.11. Skeletal structures of some metal carbide clusters. In [Osio(CO)24C], 4 of the 10 osmium atoms cap a tetrahedrally related set of faces of the inner Oss octahedron that contains the core carbon atom.

Tachikawa, Mamoru and Muetterties, E. L., Metal Carbide Clusters. . Takikawa, Osamu, see Hayaishi, Osamu Tasker, Peter A., see Hemick, Kim... 

Mass spectrometry, which is the only technique that can be used to characterize met-cars and related metal-carbide clusters, implies that the detected clusters are ionized. This requirement opens a route to a variety of experimental procedures enabling insight to be gained into physical properties such as ionization energies, electron affinities, structure, and collective electronic properties such as thermionic electron emission and delayed atomic ion emission. 

In the experiments discussed in earlier sections, the separation of the metal carbide cluster ions produced either directly in the source or in the carrier gas was exclusively performed on a mass criterion. Ion chromatography experiments performed by Bowers and co-workers introduce another selection criterion by allowing a mass-selected ion cloud to undergo collisions with a He buffer gas in a drift cell [28,68] given species will depend on its collision cross section... 

Several techniques have been used to investigate the reactivity of the metal carbide cluster ions formed in a laser vaporization source. The earliest investigations performed by Castleman s group relied on a preliminary mass selection of the desired cluster. The ion beam was then injected into a drift tube where the selected cluster encounters the reactant mixed with helium as a buffer gas. The FTICR (Fourier-transform ion cyclotron resonance) mass spectrometer studies reported by Byun, Freiser and co-workers basically rely on the same principle even though the total pressure of the reaction chamber is 10 torr, compared with 0.7 torr in Castleman s experiments. A new method of forming met-car ligand complexes was then reported by Castleman et al. this involved the direct interaction of the vaporized metal with mixtures of methane and selected reactant gases. ... 

S.9.4.5. Oxidation-induced reactions of TigCii and other metal-carbide clusters... 

Shibuta, et al. Bond-Order Potential for Transition Metal Carbide Cluster for the Growth Simulation of a Single-Walled Carbon Nanotube. Department of Materials Engineering, The University of Tokyo 2003. 

Andriotis, A. N., Menon, M., Eroudakis, G. E., Lowther, J. E. (1999). Tight-binding molecular dynamics study of transition metal carbide clusters. Chemical Physics Letters, 301, 503. 

In recent years a great number of transition metal clusters containing an interstitial carbon atom has been prepared and now they constitute a growing field of metal carbide clusters . A far less number of nitride clusters and several compounds containing a naked P, As, or S atom embedded within metal clusters have been reported, such as... 

Y. Shibuta and S. Maruyama. Bond-order potential for transition metal carbide cluster for the growth simulation of a single-waUed carbon nanotube. Comput. Mater. Sci. 39, 2007, 842-848. 

---