Mixed metal carbide clusters

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 ... 

MIXED METAL-CARBON CLUSTERS AND METAL CARBIDES... 

The number of heterometallic nitrido clusters so far synthesized is limited, and the majority of these compounds are a result of non-systematic studies. In contrast, many examples of mixed metal carbides are known,the investigations rising from the pioneering work of Muetterties - on iron-containing species. 

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. ... 

Although the conversion of a particular carbido cluster into another with a different metal framework is an important synthetic method for carbides (1), the analogous process is essentially untapped for nitrido clusters. It has been used [Eq. (56)] to form the largest known nitrido cluster, [PtRhioN(CO)2i ] (29) (%), and it proved successful in adding a fifth vertex in the formation of the mixed-metal cluster [FeRu4N(CO)i4] [Eq. (57)] (43). 

The chemistry of both Ru-W and Os-W mixed-metal clusters was extensively investigated by Chi et al., and a number of exciting discoveries were made. These include the reversible scission of a coordinated acetylide ligand on the acetylide cluster 168, which can be prepared from the condensation of CpW(CO)3(C2Ph) and Ru3(GO)i2 in refluxing toluene.The carbide clusters 169 and 170 were formed when 168 was heated with Ru3(CO)i2 in heptane. Interestingly, the reaction sequence can be reversed to regenerate the acetylide cluster 168 in the presence of pressurized CO. This kind of reactivity is seldom observed for semi-encapsulated ruthenium carbide systems. 

Laser pyrolysis This is based on the heating with a laser beam of an organometallic reactantvapor (e.g., a metal carbonyl), mixed with an inert gas. The reactant vapors rapidly decompose to the atoms, which form clusters upon collision with inert gas molecules [29]. Nanoparticles of iron and iron carbides have been prepared in this way. 

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